Endectocides for malaria control

Electropenetrography with Alternating Current Reveals In Situ Changes of Aedes aegypti Probing Behaviors Associated with Dengue Virus Infection

Human infection with dengue virus (DENV) results in significant morbidity and mortality around the world. Current methods to investigate virus-associated changes in insect feeding behaviors are largely restricted to video analysis of feeding events outside of the host or intravital microscopy. Electropenetrography, a method originally developed for plant-feeding insects, offers a promising alternative by allowing high-resolution recording of voltage changes across the insect bite interface. We compared recordings from DENV-infected Aedes aegypti mosquitoes feeding on uninfected mice and uninfected A. aegypti feeding on DENV-infected mice to controls of uninfected A. aegypti feeding on uninfected mice. We found significant mosquito behavioral changes in both DENV-infected groups compared with controls including longer feeding times and longer preingestion probing events for A. aegypti feeding on DENV-infected mice and a higher number of sequential probing events in DENV-infected A. aegypti feeding on uninfected mice. By recording mosquito feeding and probing events beneath the surface of the skin, we have been able to both confirm and add new dimensions to previous findings regarding DENV-associated behavior changes in A. aegypti. This provides a foundation for increasingly in-depth studies focusing on the transmission of the DENV between vectors and hosts.

Evaluation of the mosquitocidal efficacy of fluralaner, a potential candidate for drug based vector control

Vector control is a key intervention against mosquito borne diseases. However, conventional methods have several limitations and alternate strategies are in urgent need. Vector control with endectocides such as ivermectin is emerging as a novel strategy. The short half-life of ivermectin is a limiting factor for its application as a mass therapy tool for vector control. Isoxazoline compounds like fluralaner, a class of veterinary acaricides with long half-life hold promise as an alternative. However, information about their mosquitocidal effect is limited. We explored the efficacy of fluralaner against laboratory reared vector mosquitoes-Aedes aegypti, Anopheles stephensi, and, Culex quinquefasciatus. 24 h post-blood feeding, fluralaner showed a significant mosquitocidal effect with LC50 values in the range of 24.04-49.82 ng/mL for the three different mosquito species tested. Effects on life history characteristics (fecundity, egg hatch success, etc.) were also observed and significant effects were noted at drug concentrations of 20, 25 and 45 ng/mL for Ae. aegypti, An. stephensi, and, Cx. quinquefasciatus respectively. At higher drug concentration of 250 ng/mL, significant mortality was observed within 1-2 h of post blood feeding. Potent mosquitocidal effect coupled with its long half-life makes fluralaner an excellent candidate for drug based vector control strategies.

Simian malaria: a narrative review on emergence, epidemiology and threat to global malaria elimination

Simian malaria from wild non-human primate populations is increasingly recognised as a public health threat and is now the main cause of human malaria in Malaysia and some regions of Brazil. In 2022, Malaysia became the first country not to achieve malaria elimination due to zoonotic simian malaria. We review the global distribution and drivers of simian malaria and identify priorities for diagnosis, treatment, surveillance, and control. Environmental change is driving closer interactions between humans and wildlife, with malaria parasites from non-human primates spilling over into human populations and human malaria parasites spilling back into wild non-human primate populations. These complex transmission cycles require new molecular and epidemiological approaches to track parasite spread. Current methods of malaria control are ineffective, with wildlife reservoirs and primarily outdoor-biting mosquito vectors urgently requiring the development of novel control strategies. Without these, simian malaria has the potential to undermine malaria elimination globally.

Effect of fluralaner on the biology, survival, and reproductive fitness of the neotropical malaria vector Anopheles aquasalis

BACKGROUND

Reducing mosquito abundance or interfering with its ability to support the parasite cycle can help to interrupt malaria in areas of significant risk of malaria transmission. Fluralaner is a safe and effective drug for veterinary use indicated for the treatment against fleas and ticks which acts as an antagonist of chloride ion channels mediated by γ-aminobutyric acid (GABA), preventing the entry of these ions into the postsynaptic neuron, leading to hyperexcitability of the postsynaptic neuron of the central nervous system of arthropods. Fluralaner demonstrated insecticidal activity against different insect species.

METHODS

The study aimed to evaluate the effects of fluralaner on the biology, survival, and reproductive fitness of Anopheles aquasalis. The following lethal concentrations (LC) were determined for An. aquasalis: LC5 = 0.511 µM; LC25 = 1.625 µM; LC50 = 3.237 µM.

RESULTS

A significant decrease (P < 0.001) was evident in the number of eggs, larvae, and pupae in the group exposed to a sublethal dose of fluralaner when compared to a control group (without the drug). Using blood from dogs after administration of fluralaner, it was observed that the drug causes 100% mortality in An. aquasalis in less than 24 h after feeding; this effect remains even after 90 days in all samples.

DISCUSSION

Fluralaner showed the same result for up to 60 days, and after that, there was a slight reduction in its effect, evidenced by a decrease in the percentage of dead females; however, still significant when compared to the control group.

CONCLUSION

Fluralaner affects the biology and reduction of survival in An. aquasalis in a lasting and prolonged period, and its fecundity with lower dosages, is a strong candidate for controlling disease vectors.

Ivermectin systemic availability in adult volunteers treated with different oral pharmaceutical formulations

Ivermectin (IVM) is currently approved as an antiparasitic agent for human use in the treatment of onchocerciasis, lymphatic filariasis, strongyloidiasis, scabies, and pediculosis. Recent findings indicate that IVM may reach other pharmacological targets, which accounts for its proven anti-inflammatory/immunomodulatory, cytostatic, and antiviral effects. However, little is known about the assessment of alternative drug formulations for human use.

OBJECTIVE

To compare the systemic availability and disposition kinetics of IVM orally administered as different pharmaceutical formulations (tablet, solution, or capsule) to healthy adults.

EXPERIMENTAL DESIGN/MAIN FINDINGS

Volunteers were randomly assigned to 1 of 3 experimental groups and orally treated with IVM as either, a tablet, solution, or capsules at 0.4 mg/kg in a three-phase crossover design. Blood samples were taken as dried blood spots (DBS) between 2 and 48 h post-treatment and IVM was analyzed by HPLC with fluorescence detection. IVM Cmax value was higher (P < 0.05) after the administration of the oral solution compared to treatments with both solid preparations. The oral solution resulted in a significantly higher IVM systemic exposure (AUC: 1653 ng h/mL) compared to the tablet (1056 ng h/mL) and capsule (996 ng h/mL) formulations. The simulation of a 5-day repeated administration for each formulation did not show a significant systemic accumulation.

CONCLUSION

Beneficial effects against systemically located parasitic infections as well as in any other potential therapeutic field of IVM application would be expected from its use in the form of oral solution. This pharmacokinetic-based therapeutic advantage without the risk of excessive accumulation needs to be corroborated in clinical trials specifically designed for each purpose.

Repeat Ivermectin Mass Drug Administrations for Malaria Control II: Protocol for a Double-blind, Cluster-Randomized, Placebo-Controlled Trial for the Integrated Control of Malaria

BACKGROUND

The gains made against malaria have stagnated since 2015, threatened further by increasing resistance to insecticides and antimalarials. Improvement in malaria control necessitates a multipronged strategy, which includes the development of novel tools. One such tool is mass drug administration (MDA) with endectocides, primarily ivermectin, which has shown promise in reducing malaria transmission through lethal and sublethal impacts on the mosquito vector.

OBJECTIVE

The primary objective of the study is to assess the impact of repeated ivermectin MDA on malaria incidence in children aged ≤10 years.

METHODS

Repeat Ivermectin MDA for Malaria Control II is a double-blind, placebo-controlled, cluster-randomized, and parallel-group trial conducted in a setting with intense seasonal malaria transmission in Southwest Burkina Faso. The study included 14 discrete villages: 7 (50%) randomized to receive standard measures (seasonal malaria chemoprevention [SMC] and bed net use for children aged 3 to 59 months) and placebo, and 7 (50%) randomized to receive standard measures and monthly ivermectin MDA at 300 μg/kg for 3 consecutive days, provided under supervision to all eligible village inhabitants, over 2 successive rainy seasons. Nonpregnant individuals >90 cm in height were eligible for ivermectin MDA, and cotreatment with ivermectin and SMC was not permitted. The primary outcome is malaria incidence in children aged ≤10 years, as assessed by active case surveillance. The secondary safety outcome of repeated ivermectin MDA was assessed through active and passive adverse event monitoring.

RESULTS

The trial intervention was conducted from July to November in 2019 and 2020, with additional sampling of humans and mosquitoes occurring through February 2022 to assess postintervention changes in transmission patterns. Additional human and entomological assessments were performed over the 2 years in a subset of households from 6 cross-sectional villages. A subset of individuals underwent additional sampling in 2020 to characterize ivermectin pharmacokinetics and pharmacodynamics. Analysis and unblinding will commence once the database has been completed, cleaned, and locked.

CONCLUSIONS

Our trial represents the first study to directly assess the impact of a novel approach for malaria control, ivermectin MDA as a mosquitocidal agent, layered into existing standard-of-care interventions. The study was designed to leverage the current SMC deployment infrastructure and will provide evidence regarding the additional benefit of ivermectin MDA in reducing malaria incidence in children.

TRIAL REGISTRATIONS

ClinicalTrials.gov NCT03967054; https://clinicaltrials.gov/ct2/show/NCT03967054 and Pan African Clinical Trials Registry PACT201907479787308; https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=8219.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/41197.

Effect of Ivermectin® on survivorship and fertility of Anopheles arabiensis in Ethiopia: an in vitro study

BACKGROUND

Innovative vector control tools are needed to counteract insecticide resistance and residual malaria transmission. One of such innovative methods is an ivermectin (IVM) treatment to reduce vector survival. In this study, a laboratory experiment was conducted to investigate the effect of ivermectin on survivorship, fertility and egg hatchability rate of Anopheles arabiensis in Ethiopia.

METHODS

An in vitro experiment was conducted using 3-5 days old An. arabiensis adults from a colony maintained at insectary of Tropical and Infectious Diseases Research Center, Jimma University (laboratory population) and Anopheles mosquitoes reared from larvae collected from natural mosquito breeding sites (wild population). The mosquitoes were allowed to feed on cattle blood treated with different doses of ivermectin (0 ng/ml, 5 ng/ml, 10 ng/ml, 20 ng/ml, 40 ng/ml and 80 ng/ml). During each feeding experiment, the mosquitoes were held in cages and blood-fed using a Hemotek feeder. Mortality and egg production were then recorded daily for up to 9 days. Time to death was analysed by a Cox frailty model with replicate as frailty term and source of mosquito (wild versus laboratory), treatment type (ivermectin vs control) and their interaction as categorical fixed effects. Kaplan Meier curves were plotted separately for wild and laboratory populations for a visual interpretation of mosquito survival as a function of treatment.

RESULTS

Both mosquito source and treatment had a significant effect on survival (P < 0.001), but their interaction was not significant (P = 0.197). Compared to the controls, the death hazard of An. arabiensis that fed on ivermectin-treated blood was 2.3, 3.5, 6.5, 11.5 and 17.9 times that of the control for the 5 ng/ml, 10 ng/ml, 20 ng/ml, 40 ng/ml, and 80 ng/ml dose, respectively. With respect to the number of hatched larvae, hatched pupae and emerged adults per fed mosquitoes, a significant difference was found between the control and the 5 ng/ml dose group (P < 0.001). The number of hatched larvae and pupae, and emerged adults decreased further for the 10 ng/ml dose group and falls to zero for the higher doses.

CONCLUSION

Treating cattle blood with ivermectin reduced mosquito survival, fertility, egg hatchability, larval development and adult emergence of An. arabiensis in all tested concentrations of ivermectin in both the wild and laboratory populations. Thus, ivermectin application in cattle could be used as a supplementary vector control method to tackle residual malaria transmission and ultimately achieve malaria elimination in Ethiopia.

Potential of ivermectin as an active ingredient of the attractive toxic sugar baits against the Indian malaria vectors Anopheles culicifacies and Anopheles stephensi

BACKGROUND

Attractive toxic sugar bait (ATSB) is a novel vector control tool that exploits the sugar feeding behavior of mosquitoes. The current study aims to evaluate the efficacy of ivermectin-based ATSB against insecticide susceptible and resistant strains of major Indian malaria vectors - Anopheles culicifacies and Anopheles stephensi. ATSB with different concentrations of ivermectin were tested against mosquito vectors under standard laboratory conditions.

RESULTS

Dose-response analysis of ivermectin-ATSB showed 7.8 and 19.8 ppm as 50% and 90% lethal concentration (LC₅₀ and LC₉₀ ) values for insecticide susceptible An. culicifacies. In the case of insecticide susceptible An. stephensi, the LC₉₀ value was 35 ppm which was significantly higher in comparison to the LC₉₀ for An. culicifacies. The LC₅₀ of insecticide-resistant An. culicifacies and An. stephensi were 10.6 and 15.9 ppm respectively whereas LC₉₀ values were 36.9 and 61.0. Ivermectin-ATSB resulted in 99 ± 0.8% mortality of An. culicifacies and 93 ± 3.8% mortality of An. stephensi at an ivermectin concentration of 25 ppm. In another set of experiments, the ATSB solution containing standardized dose of ivermectin was sprayed on Allysum plant and mortality of both Anopheline vectors was recorded. Here, we observed > 90% mortality in both An. stephensi and An. culicifacies.

CONCLUSION

Our study demonstrates the potential of ivermectin-based ATSB in killing Indian malaria vectors irrespective of the method of application. Further field trials with ivermectin containing ATSB may pave the way for its usage in the national vector control program. © 2022 Society of Chemical Industry.

Social acceptance of livestock-administered endectocides for malaria control in Vhembe District, Limpopo Province, South Africa

BACKGROUND

Malaria continues to be a leading cause of morbidity and mortality in Africa and conventional malaria control strategies, such as indoor residual spraying and insecticide-treated bed nets, have limited effectiveness for some malarial vectors. Consequently, the development of alternative or supplementary strategies is required. One potential strategy is the use of livestock-administered endectocides to control vector mosquitoes that feed outdoors on livestock. However, since this strategy requires support from local communities and livestock owners consenting for their animals to be treated, it can only be implemented if agreed to by affected communities. The aim of this study was to assess the social acceptance of the use of livestock-administered endectocides in the malaria endemic villages of Vhembe District, Limpopo Province, South Africa, where malaria incidence is high.

METHODS

Questionnaires were administered to 103 livestock-owning households from four villages, namely, Gumbu, Malale, Manenzhe and Bale. The assessment included questions on the acceptability of the strategy, the type and number of livestock owned, distances between houses and kraals (overnight pens) as well as previous use and awareness of endectocides. The results were analysed using descriptive statistics and multinomial logistic regression.

RESULTS

The types of livestock owned by the participants comprised, cattle, goats, sheep and donkeys, with the most dominant being goats (n = 1040) and cattle (n = 964). The majority of kraals were less than 10 m from homesteads. Most participants (72.5%) were already using chemicals to treat their livestock for parasites. All participants were amenable to the implementation of the strategy, and would give consent for their animals to be treated by endectocides.

CONCLUSIONS

The use of livestock-administered endectocides appears to be a feasible and acceptable approach for control of animal-feeding malaria vector species in the malaria endemic villages of Vhembe District. This is based on a high percentage of rural residents keeping suitable livestock close to their homes and expressing willingness to use endectocides for mosquito control.

Mass drug administration of ivermectin and dihydroartemisinin-piperaquine against malaria in settings with high coverage of standard control interventions: a cluster-randomised controlled trial in The Gambia

BACKGROUND

Although the malaria burden has substantially decreased in sub-Saharan Africa, progress has stalled. We assessed whether mass administration of ivermectin (a mosquitocidal drug) and dihydroartemisinin-piperaquine (an antimalarial treatment) reduces malaria in The Gambia, an area with high coverage of standard control interventions.

METHODS

This open-label, cluster-randomised controlled trial was done in the Upper River region of eastern Gambia. Villages with a baseline Plasmodium falciparum prevalence of 7-46% (all ages) and separated from each other by at least 3 km to reduce vector spillover were selected. Inclusion criteria were age and anthropometry (for ivermectin, weight of ≥15 kg; for dihydroartemisinin-piperaquine, participants older than 6 months); willingness to comply with trial procedures; and written informed consent. Villages were randomised (1:1) to either the intervention (ivermectin [orally at 300-400 μg/kg per day for 3 consecutive days] and dihydroartemisinin-piperaquine [orally depending on bodyweight] plus standard control interventions) or the control group (standard control interventions) using computer-based randomisation. Laboratory staff were masked to the origin of samples. In the intervention group, three rounds of mass drug administration once per month with ivermectin and dihydroartemisinin-piperaquine were given during two malaria transmission seasons from Aug 27 to Oct 31, 2018, and from July 15 to Sept 30, 2019. Primary outcomes were malaria prevalence by qPCR at the end of the second intervention year in November 2019, and Anopheles gambiae (s l) parous rate, analysed in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, NCT03576313.

FINDINGS

Between Nov 20 and Dec 7, 2017, 47 villages were screened for eligibility in the study. 15 were excluded because the baseline malaria prevalence was less than 7% (figure 1). 32 villages were enrolled and randomised to either the intervention or control group (n=16 in each group). The study population was 10 638, of which 4939 (46%) participants were in intervention villages. Coverage for dihydroartemisinin-piperaquine was between 49·0% and 58·4% in 2018, and between 76·1% and 86·0% in 2019; for ivermectin, coverage was between 46·9% and 52·2% in 2018, and between 71·7% and 82·9% in 2019. In November 2019, malaria prevalence was 12·8% (324 of 2529) in the control group and 5·1% (140 of 2722) in the intervention group (odds ratio [OR] 0·30, 95% CI 0·16-0·59; p<0·001). A gambiae (s l) parous rate was 83·1% (552 of 664) in the control group and 81·7% (441 of 540) in the intervention group (0·90, 0·66-1·25; p=0·537). In 2019, adverse events were recorded in 386 (9·7%) of 3991 participants in round one, 201 (5·4%) of 3750 in round two, and 168 (4·5%) of 3752 in round three. None of the 11 serious adverse events were related to the intervention.

INTERPRETATION

The intervention was safe and well tolerated. In an area with high coverage of standard control interventions, mass drug administration of ivermectin and dihydroartemisinin-piperaquine significantly reduced malaria prevalence; however, no effect of ivermectin on vector parous rate was observed.

FUNDING

Joint Global Health Trials Scheme.

TRANSLATION

For the French translation of the abstract see Supplementary Materials section.

On the use of inhibitors of 4-hydroxyphenylpyruvate dioxygenase as a vector-selective insecticide in the control of mosquitoes

BACKGROUND

Blood-sucking insects incorporate many times their body weight of blood in a single meal. Because proteins are the major component of vertebrate blood, its digestion in the gut generates extremely high concentrations of free amino acids. Previous reports showed that the tyrosine degradation pathway plays an essential role in adapting these animals to blood feeding. Inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD), the rate-limiting step of tyrosine degradation, results in the death of insects after a blood meal. Therefore, it has been suggested that compounds that block the catabolism of tyrosine could act selectively on blood-feeding insects. Here, we evaluated the toxicity against mosquitoes of three HPPD inhibitors currently used as herbicides and in human health.

RESULTS

Of the compounds tested, nitisinone (NTBC) proved to be more potent than mesotrione (MES) and isoxaflutole (IFT) in Aedes aegypti. NTBC was lethal to Ae. aegypti in artificial feeding assays [median lethal dose (LD₅₀ ): 4.53 μm] and in topical application (LD₅₀ : 0.012 nmol/mosquito). NTBC was also lethal to Ae. aegypti populations that were resistant to neurotoxic insecticides, and to other mosquito species (Anopheles and Culex).

CONCLUSION

HPPD inhibitors, particularly NTBC, represent promising new drugs for mosquito control. Because they affect only blood-feeding organisms, they represent a safer and more environmentally friendly alternative to conventional neurotoxic insecticides. © 2021 Society of Chemical Industry.

Evaluation of an ivermectin-based attractive targeted sugar bait (ATSB) against Aedes aegypti in Tanzania

Background The control of vector borne arboviral diseases such as Dengue is mainly achieved by reducing human-vector contact and controlling the vectors through source reduction and environmental management. These measures are constrained by labour intensity, insecticide resistance and pro-active community participation. The current study intended to develop and test an ivermectin-based attractive-targeted sugar bait (ATSB) against Aedes aegypti. Methods The 48hour lethal concentration (LC90) of ivermectin against Ae. aegypti was determined through serial dilution experiment where five 30cm x 30cm x 30cm cages were set; into each, a 10% sugar solution treated with ivermectin were introduced. 40 Ae. aegypti were released into each cage and observed for mortality after 4, 8, 24 and 48 hours. The ivermectin-based ATSB was evaluated in a semi field system where ATSB and attractive sugar bait (ASB) were deployed into each compartment of the semi field and 100 female Ae. aegypti were released every day and recaptured the next day through human land catch and Bio-gent sentinel trap. The developed and semi-field tested ATSB was further tested in the field by deploying them in garages. Results The ivermectin 48hr LC90 of male and female Ae. aegypti was found to be 0.03% w/v. In the semi field system, the ATSB significantly reduced a free-flying population of Ae. aegypti within 24 hours (incidence rate ratio (IRR) = 0.62; [95% confidence interval (95%CI); 0.54-0.70] and p-value < 0.001). However, in the field, the ATSBs required the addition of yeast as a carbon dioxide source to efficiently attract Ae. aegypti mosquitoes to feed. Conclusion Ivermectin is an active ingredient that can be used in an ATSB for Ae. aegypti depopulation. However, further research is needed to improve the developed and tested ATSB to compete with natural sources of sugar in a natural environment.

Insecticide-treated livestock: a potential One Health approach to malaria control in Africa

New vector-control tools are urgently needed to reduce malaria in areas where there is significant transmission after deployment of indoor residual spraying (IRS) and insecticide treated nets. Insecticide-treated livestock (ITL) is a potential novel strategy by which zoophagic mosquitos are killed after feeding upon animals treated with an insecticide. Although there are several insecticide candidates in the pipeline with a wide efficacy range against mosquitos, additional field studies with epidemiological outcomes are required to test the impact of this intervention on malaria transmission. Insecticides under consideration have long been used in livestock to improve animal health and productivity, but each has food and environmental safety considerations. Therefore, moving ITL from a concept to implementation will require a One Health framework.

Drug Repositioning: Antimalarial Activities of GABA Analogs in Mice Infected with Plasmodium berghei

BACKGROUND

Drug repositioning is becoming popular due to the development of resistance to almost all the recommended antimalarials. Pregabalin and gabapentin are chemical analogs of gamma- aminobutyric acid (GABA) approved for the treatment of epilepsy and neuropathic pain.

OBJECTIVE

This study investigates acute toxicities and antimalarial activities of pregabalin and gabapentin in the murine malarial model.

METHODS

Acute toxicities were assessed using the method of Lorke, while curative activities were assessed by the administration of serial doses of pregabalin and gabapentin to Plasmodium berghei infected mice. Pregabalin was further investigated for its prophylactic activity, and curative potential when combined with either artesunate or amodiaquine. All drugs were freshly prepared and administered orally. Thin films were collected, stained, and observed under the microscope for the estimation of parasitemia and calculation of percentage chemoinhibition or chemoprevention. In pregabalin -artesunate or -amodiaquine combination aspect of this study, survival day post-infection (SDPI) was recorded, while parasitemia was re-estimated for animals that survived till day 28.

RESULTS

The oral LD50 of gabapentin, as well as pregabalin, was >5,000 mg/kg. Gabapentin at 100 and 200 mg/Kg demonstrated 35.64% and -12.78% chemoinhibition, respectively, while pregabalin demonstrated 75.60% and 100.00% chemoinhibition at doses of 12.5 and 25 mg/Kg, respectively. Moreover, pregabalin at individual doses of 25, 50 mg/Kg, and in combination with either artesunate or amodiaquine demonstrated 100.00% chemoinhibition. In its prophylactic study, pregabalin was found to be 100% chemopreventive at individual doses of 12.5 and 25 mg/Kg.

CONCLUSION

Both GABA analogs have antimalarial properties, but pregabalin proved to be more efficacious.

Ivermectin: A Promising Therapeutic for Fighting Malaria. Current Status and Perspective

Finding new chemotherapeutic interventions to treat malaria through repurposing of time-tested drugs and rigorous design of new drugs using tools of rational drug design remains one of the most sought strategies at the disposal of medicinal chemists. Ivermectin, a semisynthetic derivative of avermectin B₁, is among the efficacious drugs used in mass drug administration drives employed against onchocerciasis, lymphatic filariasis, and several other parasitic diseases in humans. In this review, we present the prowess of ivermectin, a potent endectocide, in the control of malaria through vector control to reduce parasite transmission combined with efficacious chemoprevention to reduce malaria-related fatalities.

The effect of cattle-administered ivermectin and fipronil on the mortality and fecundity of Anopheles arabiensis Patton

Background

Malaria control primarily depends on two vector control strategies: indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs). Both IRS and LLIN target indoor-biting mosquitoes. However, some of the most important malaria vectors have developed resistance against the chemical compounds used in IRS and LLINs. Insecticide-induced behavioural changes in vectors, such as increased outdoor feeding on cattle and other animals, also limit the effectiveness of these strategies. Novel vector control strategies must therefore be found to complement IRS and LLINs. A promising tool is the use of cattle-applied endectocides. Endectocides are broad-spectrum systemic drugs that are effective against a range of internal nematodes parasites and blood-feeding arthropods. The aim of this study was to investigate the effect of two endectocide drugs, injectable ivermectin and topical fipronil, on the survival and fecundity of zoophilic Anopheles arabiensis.

Methods

Laboratory-reared mosquitoes were allowed to feed on cattle treated with either injectable ivermectin (0.2 mg/kg), topical fipronil (1.0 mg/kg) or saline (control) on days 0, 1, 4, 7, 13, 21 and 25 post-treatment, and mortality and egg production were recorded daily.

Results

Compared to controls, the mortality of An. arabiensis increased by 3.52- and 2.43-fold with injectable ivermectin and topical fipronil, respectively. The overall fecundity of mosquitoes that fed on both ivermectin- and fipronil-treated cattle was significantly reduced by up to 90 and 60%, respectively, compared to the control group. The effects of both drugs attenuated over a period of 3 weeks. Injectable ivermectin was more effective than topical fipronil and increased mosquito mortality by a risk factor of 1.51 higher than fipronil. Similarly, both drugs significantly reduced the fecundity of An. arabiensis.

Conclusions

This study demonstrates that injectable ivermectin and topical fipronil are able to suppress An. arabiensis density and could help to reduce outdoor malaria transmission. Data from the present study as well as from other similar studies suggest that current-generation endectocides have a limited duration of action and are expensive. However, new-generation, sustained-release formulations of ivermectin have a multi-week, high mortality impact on vector populations, thus holding promise of an effective reduction of outdoor malaria transmission.

Graphical abstract

From informed consent to adherence: factors influencing involvement in mass drug administration with ivermectin for malaria elimination in The Gambia

Background

The World Health Organization (WHO) recommends consideration of mass drug administration (MDA) for malaria control in low-endemic settings approaching elimination. However, MDA remains a controversial strategy, as multiple individual, social, and operational factors have shown to affect its acceptability at local levels. This is further complicated by inconsistent definitions of key indicators derived from individual and community involvement—coverage, adherence, and compliance—that cast doubts about the actual and potential epidemiological impact of MDA on disease control and elimination. This study aimed to identify limitations and enabling factors impacting involvement at different stages of a large cluster-randomized trial assessing the effect of combining dihydroartemisinin-piperaquine (DP) and ivermectin (IVM) in malaria transmission in The Gambia.

Methods

This social science study used a mixed-methods approach. Qualitative data were collected in intervention and control villages through ethnographic methods, including in-depth interviews (IDIs), focus group discussions (FGDs), and participant observation conducted with trial participants and decliners, community leaders, and field staff. A cross-sectional survey was conducted in the intervention villages after the first year of MDA. Both strands of the study explored malaria knowledge and opinions, social dynamics influencing decision-making, as well as perceived risks, burdens, and benefits associated with this MDA.

Results

157 IDIs and 11 FGDs were conducted, and 864 respondents were included in the survey. Barriers and enabling factors to involvement were differentially influential at the various stages of the MDA. Issues of social influence, concerns regarding secondary effects of the medication, costs associated with malaria, and acceptability of the implementing organization, among other factors, differently affected the decision-making processes throughout the trial. Rather than a linear trajectory, involvement in this MDA trial was subjected to multiple revaluations from enrolment and consent to medicine intake and adherence to treatment.

Conclusions

This study went beyond the individual factors often associated with coverage and adherence, and found that nuanced social dynamics greatly influence the decision-making process at all phases of the trial. These issues need to be consider for MDA implementation strategies and inform discussions about more accurate ways of reporting on critical effectiveness indicators.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03732-z.

Drug Repurposing: A Review of Old and New Antibiotics for the Treatment of Malaria: Identifying Antibiotics with a Fast Onset of Antiplasmodial Action

Malaria is one of the most life-threatening infectious diseases and constitutes a major health problem, especially in Africa. Although artemisinin combination therapies remain efficacious to treat malaria, the emergence of resistant parasites emphasizes the urgent need of new alternative chemotherapies. One strategy is the repurposing of existing drugs. Herein, we reviewed the antimalarial effects of marketed antibiotics, and described in detail the fast-acting antibiotics that showed activity in nanomolar concentrations. Antibiotics have been used for prophylaxis and treatment of malaria for many years and are of particular interest because they might exert a different mode of action than current antimalarials, and can be used simultaneously to treat concomitant bacterial infections.

Quantifying individual variability in exposure risk to mosquito bites in the Cascades region, Burkina Faso

Background

The Cascades region, Burkina Faso, has a high malaria burden despite reported high insecticide-treated mosquito net (ITN) use. Human and vector activities outside the hours when indoor interventions offer direct protection from infectious bites potentially increase exposure risk to bites from malaria-transmitting Anopheles mosquitoes. This work investigated the degree of variation in human behaviour both between individuals and through time (season) to quantify how it impacts exposure to malaria vectors.

Methods

Patterns in human overnight activity (18:00–06:00) to quantify time spent using an ITN across 7 successive nights in two rural communities, Niakore (N = 24 participants) and Toma (71 participants), were observed in the dry and rainy seasons, between 2017 and 2018. Hourly human landing Anopheles mosquito catches were conducted in Niakore specifically, and Cascades region generally, between 2016 and 2017. Data were statistically combined to estimate seasonal variation in time spent outdoors and Anopheles bites received per person per night (bpppn).

Results

Substantial variability in exposure to outdoor Anopheles bites was detected within and between communities across seasons. In October, when Anopheles densities are highest, an individual’s risk of Anopheles bites ranged from 2.2 to 52.2 bites per person per night (bpppn) within the same week with variable risk dependent on hours spent indoors. Comparably higher outdoor human activity was observed in April and July but, due to lower Anopheles densities estimated, bpppn were 0.2–4.7 and 0.5–32.0, respectively. Males and people aged over 21 years were predicted to receive more bites in both sentinel villages.

Conclusion

This work presents one of the first clear descriptions of the degree of heterogeneity in time spent outdoors between people and across the year. Appreciation of sociodemographic, cultural and entomological activities will help refine approaches to vector control.

Endectocides as a complementary intervention in the malaria control program: a systematic review

BACKGROUND

Malaria is the most common vector-borne disease transmitted to humans by Anopheles mosquitoes. Endectocides and especially ivermectin will be available as a vector control tool soon. The current review could be valuable for trial design and clinical studies to control malaria transmission.

METHODS

PubMed/MEDLINE, Scopus, Web of Science, and Science Direct were searched for original English published papers on ("Malaria chemical control" OR "Malaria elimination" OR "Anopheles vector control" OR "Malaria zooprophylaxis") AND ("Systemic insecticides" OR "Endectocides" OR "Ivermectin"). The last search was from 19 June 2019 to 31 December 2019. It was updated on 17 November 2020. Two reviewers (SG and FGK) independently reviewed abstracts and full-text articles. Data were extracted by one person and checked by another. As meta-analyses were not possible, a qualitative summary of results was performed.

RESULTS

Thirty-six published papers have used systemic insecticides/endectocides for mosquito control. Most of the studies (56.75%) were done on Anopheles gambiae complex species on doses from 150 μg/kg to 400 μg/kg in several studies. Target hosts for employing systemic insecticides/drugs were animals (44.2%, including rabbit, cattle, pig, and livestock) and humans (32.35%).

CONCLUSIONS

Laboratory and field studies have highlighted the potential of endectocides in malaria control. Ivermectin and other endectocides could soon serve as novel malaria transmission control tools by reducing the longevity of Anopheles mosquitoes that feed on treated hosts, potentially decreasing Plasmodium parasite transmission when used as mass drug administration (MDA).

Widespread zoophagy and detection of Plasmodium spp. in Anopheles mosquitoes in southeastern Madagascar

BACKGROUND

Malaria is a top cause of mortality on the island nation of Madagascar, where many rural communities rely on subsistence agriculture and livestock production. Understanding feeding behaviours of Anopheles in this landscape is crucial for optimizing malaria control and prevention strategies. Previous studies in southeastern Madagascar have shown that Anopheles mosquitoes are more frequently captured within 50 m of livestock. However, it remains unknown whether these mosquitoes preferentially feed on livestock. Here, mosquito blood meal sources and Plasmodium sporozoite rates were determined to evaluate patterns of feeding behaviour in Anopheles spp. and malaria transmission in southeastern Madagascar.

METHODS

Across a habitat gradient in southeastern Madagascar 7762 female Anopheles spp. mosquitoes were collected. Of the captured mosquitoes, 492 were visibly blood fed and morphologically identifiable, and a direct enzyme-linked immunosorbent assay (ELISA) was used to test for swine, cattle, chicken, human, and dog blood among these specimens. Host species identification was confirmed for multiple blood meals using PCR along with Sanger sequencing. Additionally, 1,607 Anopheles spp. were screened for the presence of Plasmodium falciparum, P. vivax-210, and P. vivax 247 circumsporozoites (cs) by ELISA.

RESULTS

Cattle and swine accounted, respectively, for 51% and 41% of all blood meals, with the remaining 8% split between domesticated animals and humans. Of the 1,607 Anopheles spp. screened for Plasmodium falciparum, Plasmodium vivax 210, and Plasmodium vivax 247 cs-protein, 45 tested positive, the most prevalent being P. vivax 247, followed by P. vivax 210 and P. falciparum. Both variants of P. vivax were observed in secondary vectors, including Anopheles squamosus/cydippis, Anopheles coustani, and unknown Anopheles spp. Furthermore, evidence of coinfection of P. falciparum and P. vivax 210 in Anopheles gambiae sensu lato (s.l.) was found.

CONCLUSIONS

Here, feeding behaviour of Anopheles spp. mosquitoes in southeastern Madagascar was evaluated, in a livestock rich landscape. These findings suggest largely zoophagic feeding behaviors of Anopheles spp., including An. gambiae s.l. and presence of both P. vivax and P. falciparum sporozoites in Anopheles spp. A discordance between P. vivax reports in mosquitoes and humans exists, suggesting high prevalence of P. vivax circulating in vectors in the ecosystem despite low reports of clinical vivax malaria in humans in Madagascar. Vector surveillance of P. vivax may be relevant to malaria control and elimination efforts in Madagascar. At present, the high proportion of livestock blood meals in Madagascar may play a role in buffering (zooprophylaxis) or amplifying (zoopotentiation) the impacts of malaria. With malaria vector control efforts focused on indoor feeding behaviours, complementary approaches, such as endectocide-aided vector control in livestock may be an effective strategy for malaria reduction in Madagascar.

High concentrations of membrane-fed ivermectin are required for substantial lethal and sublethal impacts on Aedes aegypti

Background

With widespread insecticide resistance in mosquito vectors, there is a pressing need to evaluate alternatives with different modes of action. Blood containing the antihelminthic drug ivermectin has been shown to have lethal and sub-lethal effects on mosquitoes. Almost all work to date has been on Anopheles spp., but impacts on other anthropophagic vectors could provide new options for their control, or additional value to anti-malarial ivermectin programmes.

Methods

Using dose-response assays, we evaluated the effects of ivermectin delivered by membrane feeding on daily mortality (up to 14 days post-blood feed) and fecundity of an Indian strain of Aedes aegypti.

Results

The 7-day lethal concentration of ivermectin required to kill 50% of adult mosquitoes was calculated to be 178.6 ng/ml (95% confidence intervals 142.3–218.4) for Ae. aegypti, which is much higher than that recorded for Anopheles spp. in any previous study. In addition, significant effects on fecundity and egg hatch rates were only recorded at high ivermectin concentrations (≥ 250 ng/ul).

Conclusion

Our results suggest that levels of ivermectin present in human blood at current dosing regimes in mass drug administration campaigns, or even those in a recent higher-dose anti-malaria trial, are unlikely to have a substantial impact on Ae. aegypti. Moreover, owing to the strong anthropophagy of Ae. aegypti, delivery of higher levels of ivermectin in livestock blood is also unlikely to be an effective option for its control. However, other potential toxic impacts of ivermectin metabolites, accumulation in tissues, sublethal effects on behaviour, or antiviral action might increase the efficacy of ivermectin against Ae. aegypti and the arboviral diseases it transmits, and require further investigation.

Repurposing the orphan drug nitisinone to control the transmission of African trypanosomiasis

Tsetse transmit African trypanosomiasis, which is a disease fatal to both humans and animals. A vaccine to protect against this disease does not exist so transmission control relies on eliminating tsetse populations. Although neurotoxic insecticides are the gold standard for insect control, they negatively impact the environment and reduce populations of insect pollinator species. Here we present a promising, environment-friendly alternative to current insecticides that targets the insect tyrosine metabolism pathway. A bloodmeal contains high levels of tyrosine, which is toxic to haematophagous insects if it is not degraded and eliminated. RNA interference (RNAi) of either the first two enzymes in the tyrosine degradation pathway (tyrosine aminotransferase (TAT) and 4-hydroxyphenylpyruvate dioxygenase (HPPD)) was lethal to tsetse. Furthermore, nitisinone (NTBC), an FDA-approved tyrosine catabolism inhibitor, killed tsetse regardless if the drug was orally or topically applied. However, oral administration of NTBC to bumblebees did not affect their survival. Using a novel mathematical model, we show that NTBC could reduce the transmission of African trypanosomiasis in sub-Saharan Africa, thus accelerating current disease elimination programmes.

Efficient degradation of ivermectin by newly isolated Aeromonas taiwanensis ZJB-18,044

Ivermectin (IVM) is a widely used antiparasitic agent and acaricide. Despite its high efficiency against nematodes and arthropods, IVM may pose a threat to the environment due to its ecotoxcity. In this study, degradation of IVM by a newly isolated bacterium Aeromonas taiwanensis ZJB-18,044 was investigated. Strain ZJB-18,044 can completely degrade 50 mg/L IVM in 5 d with a biodegradation ability of 0.42 mg/L/h. Meanwhile, it exhibited high tolerance (50 mg/L) to doramectin, emamectin, rifampicin, and spiramycin. It can also efficiently degrade doramectin, emamectin, and spiramycin. The IVM degradation of strain ZJB-18,044 can be inhibited by erythromycin, azithromycin, spiramycin or rifampicin. However, supplement of carbonyl cyanide m-chlorophenylhydrazone, an uncoupler of oxidative phosphorylation, can partially recover the IVM degradation. Moreover, strain ZJB-18,044 cells can pump out excess IVM to maintain a low intracellular IVM concentration. Therefore, the IVM tolerance of strain ZJB-18,044 may be due to the regulation of the intracellular IVM concentration by the activated macrolide efflux pump(s). With the high IVM degradation efficiency, A. taiwanensis ZJB-18,044 may serve as a bioremediation agent for IVM and other macrolides in the environment.

Avermectin Derivatives, Pharmacokinetics, Therapeutic and Toxic Dosages, Mechanism of Action, and Their Biological Effects

Avermectins are a group of drugs that occurs naturally as a product of fermenting Streptomyces avermitilis, an actinomycetes, isolated from the soil. Eight different structures, including ivermectin, abamectin, doramectin, eprinomectin, moxidectin, and selamectin, were isolated and divided into four major components (A1a, A2a, B1a and B2a) and four minor components (A1b, A2b, B1b, and B2b). Avermectins are generally used as a pesticide for the treatment of pests and parasitic worms as a result of their anthelmintic and insecticidal properties. Additionally, they possess anticancer, anti-diabetic, antiviral, antifungal, and are used for treatment of several metabolic disorders. Avermectin generally works by preventing the transmission of electrical impulse in the muscle and nerves of invertebrates, by amplifying the glutamate effects on the invertebrates-specific gated chloride channel. Avermectin has unwanted effects or reactions, especially when administered indiscriminately, which include respiratory failure, hypotension, and coma. The current review examines the mechanism of actions, biosynthesis, safety, pharmacokinetics, biological toxicity and activities of avermectins.

Repurposing Drugs to Fight Hepatic Malaria Parasites

Malaria remains one of the most prevalent infectious diseases worldwide, primarily affecting some of the most vulnerable populations around the globe. Despite achievements in the treatment of this devastating disease, there is still an urgent need for the discovery of new drugs that tackle infection by Plasmodium parasites. However, de novo drug development is a costly and time-consuming process. An alternative strategy is to evaluate the anti-plasmodial activity of compounds that are already approved for other purposes, an approach known as drug repurposing. Here, we will review efforts to assess the anti-plasmodial activity of existing drugs, with an emphasis on the obligatory and clinically silent liver stage of infection. We will also review the current knowledge on the classes of compounds that might be therapeutically relevant against Plasmodium in the context of other communicable diseases that are prevalent in regions where malaria is endemic. Repositioning existing compounds may constitute a faster solution to the current gap of prophylactic and therapeutic drugs that act on Plasmodium parasites, overall contributing to the global effort of malaria eradication.

Opinions of key stakeholders on alternative interventions for malaria control and elimination in Tanzania

Background

Malaria control in Tanzania currently relies primarily on long-lasting insecticidal nets and indoor residual spraying, alongside effective case management and behaviour change communication. This study explored opinions of key stakeholders on the national progress towards malaria elimination, the potential of currently available vector control interventions in helping achieve elimination by 2030, and the need for alternative interventions that could be used to supplement malaria elimination efforts in Tanzania.

Methods

In this exploratory qualitative study, Focus group discussions were held with policy-makers, regulators, research scientists and community members. Malaria control interventions discussed were: (a) improved housing, (b) larval source management, (c) mass drug administration (MDA) with ivermectin to reduce vector densities, (d) release of modified mosquitoes, including genetically modified or irradiated mosquitoes, (e) targeted spraying of mosquito swarms, and (f) spatial repellents.

Results

Larval source management and spatial repellents were widely supported across all stakeholder groups, while insecticide-spraying of mosquito swarms was the least preferred. Support for MDA with ivermectin was high among policy makers, regulators and research scientists, but encountered opposition among community members, who instead expressed strong support for programmes to improve housing for poor people in high transmission areas. Policy makers, however, challenged the idea of government-supported housing improvement due to its perceived high costs. Techniques of mosquito modification, specifically those involving gene drives, were viewed positively by community members, policy makers and regulators, but encountered a high degree of scepticism among scientists. Overall, policy-makers, regulators and community members trusted scientists to provide appropriate advice for decision-making.

Conclusion

Stakeholder opinions regarding alternative malaria interventions were divergent except for larval source management and spatial repellents, for which there was universal support. MDA with ivermectin, housing improvement and modified mosquitoes were also widely supported, though each faced concerns from at least one stakeholder group. While policy-makers, regulators and community members all noted their reliance on scientists to make informed decisions, their reasoning on the benefits and disadvantages of specific interventions included factors beyond technical efficiency. This study suggests the need to encourage and strengthen dialogue between research scientists, policy makers, regulators and communities regarding new interventions.

Molecular Design and Synthesis of Ivermectin Hybrids Targeting Hepatic and Erythrocytic Stages of Plasmodium Parasites

Ivermectin is a powerful endectocide, which reduces the incidence of vector-borne diseases. Besides its strong insecticidal effect on mosquito vectors of the disease, ivermectin inhibits Plasmodium falciparum sporogonic and blood stage development and impairs Plasmodium berghei development inside hepatocytes, both in vitro and in vivo. Herein, we present the first report on structural modification of ivermectin to produce dual-action molecular hybrids with good structure-dependent in vitro activity against both the hepatic and erythrocytic stages of P. berghei and P. falciparum infection, suggesting inclusion of ivermectin antimalarial hybrids in malaria control strategies. The most active hybrid displayed over threefold and 10-fold higher in vitro activity than ivermectin against hepatic and blood stage infections, respectively. Although an overwhelming insecticidal effect against Anopheles stephensi mosquitoes in laboratory conditions was not noticed, in silico docking analysis supports allosteric binding to glutamate-gated chloride channels similar to ivermectin.

A Roadmap for the Development of Ivermectin as a Complementary Malaria Vector Control Tool

In the context of stalling progress against malaria, resistance of mosquitoes to insecticides, and residual transmission, mass drug administration (MDA) of ivermectin, an endectocide used for neglected tropical diseases (NTDs), has emerged as a promising complementary vector control method. Ivermectin reduces the life span of Anopheles mosquitoes that feed on treated humans and/or livestock, potentially decreasing malaria parasite transmission when administered at the community level. Following the publication by WHO of the preferred product characteristics for endectocides as vector control tools, this roadmap provides a comprehensive view of processes needed to make ivermectin available as a vector control tool by 2024 with a completely novel mechanism of action. The roadmap covers various aspects, which include 1) the definition of optimal dosage/regimens for ivermectin MDA in both humans and livestock, 2) the risk of resistance to the drug and environmental impact, 3) ethical issues, 4) political and community engagement, 5) translation of evidence into policy, and 6) operational aspects of large-scale deployment of the drug, all in the context of a drug given as a prevention tool acting at the community level. The roadmap reflects the insights of a multidisciplinary group of global health experts who worked together to elucidate the path to inclusion of ivermectin in the toolbox against malaria, to address residual transmission, counteract insecticide resistance, and contribute to the end of this deadly disease.

Ivermectin as a novel complementary malaria control tool to reduce incidence and prevalence: a modelling study

BACKGROUND

Ivermectin is a potential new vector control tool to reduce malaria transmission. Mosquitoes feeding on a bloodmeal containing ivermectin have a reduced lifespan, meaning they are less likely to live long enough to complete sporogony and become infectious. We aimed to estimate the effect of ivermectin on malaria transmission in various scenarios of use.

METHODS

We validated an existing population-level mathematical model of the effect of ivermectin mass drug administration (MDA) on the mosquito population and malaria transmission against two datasets: clinical data from a cluster- randomised trial done in Burkina Faso in 2015 wherein ivermectin was given to individuals taller than 90 cm and entomological data from a study of mosquito outcomes after ivermectin MDA for onchocerciasis or lymphatic filariasis in Burkina Faso, Senegal, and Liberia between 2008 and 2013. We extended the existing model to include a range of complementary malaria interventions (seasonal malaria chemoprevention and MDA with dihydroartemisinin-piperaquine) and to incorporate new data on higher doses of ivermectin with a longer mosquitocidal effect. We consider two ivermectin regimens: a single dose of 400 μg/kg (1 × 400 μg/kg) and three consecutive daily doses of 300 μg/kg per day (3 × 300 μg/kg). We simulated the effect of these two doses in a range of usage scenarios in different transmission settings (highly seasonal, seasonal, and perennial). We report percentage reductions in clinical incidence and slide prevalence.

FINDINGS

We estimate that MDA with ivermectin will reduce prevalence and incidence and is most effective in areas with highly seasonal transmission. In a highly seasonal moderate transmission setting, three rounds of ivermectin only MDA at 3 × 300 μg/kg (rounds spaced 1 month apart) and 70% coverage is predicted to reduce clinical incidence by 71% and prevalence by 34%. We predict that adding ivermectin MDA to seasonal malaria chemoprevention in this setting would reduce clinical incidence by an additional 77% in children younger than 5 years compared with seasonal malaria chemoprevention alone; adding ivermectin MDA to MDA with dihydroartemisinin-piperaquine in this setting would reduce incidence by an additional 75% and prevalence by an additional 64% (all ages) compared with MDA with dihydroartemisinin-piperaquine alone.

INTERPRETATION

Our modelling predictions suggest that ivermectin could be a valuable addition to the malaria control toolbox, both in areas with persistently high transmission where existing interventions are insufficient and in areas approaching elimination to prevent resurgence.

FUNDING

Imperial College Junior Research Fellowship.

Inhibition of Plasmodium sporogonic stages by ivermectin and other avermectins

Background

The transmissible forms of Plasmodium parasites result from a process of sporogony that takes place inside their obligatory mosquito vector and culminates in the formation of mammalian-infective parasite forms. Ivermectin is a member of the avermectin family of endectocides, which has been proposed to inhibit malaria transmission due its insecticidal effect. However, it remains unclear whether ivermectin also exerts a direct action on the parasite’s blood and transmission stages.

Methods

We employed a rodent model of infection to assess the impact of ivermectin treatment on P. berghei asexual and sexual blood forms in vivo. We then made use of a newly established luminescence-based methodology to evaluate the activity of ivermectin and other avermectins against the sporogonic stages of P. berghei parasites in vitro independent of their role on mosquito physiology.

Results

Our results show that whereas ivermectin does not affect the parasite’s parasitemia, gametocytemia or exflagellation in the mammalian host, several members of the avermectin family of compounds exert a strong inhibitory effect on the generation and development of P. berghei oocysts.

Conclusions

Our results shed light on the action of avermectins against Plasmodium transmission stages and highlight the potential of these compounds to help prevent the spread of malaria.

Optimising systemic insecticide use to improve malaria control

Background

Long-lasting insecticidal nets and indoor residual sprays have significantly reduced the burden of malaria. However, several hurdles remain before elimination can be achieved: mosquito vectors have developed resistance to public health insecticides, including pyrethroids, and have altered their biting behaviour to avoid these indoor control tools. Systemic insecticides, drugs applied directly to blood hosts to kill mosquitoes that take a blood meal, offer a promising vector control option. To date, most studies focus on repurposing ivermectin, a drug used extensively to treat river blindness. There is concern that overdependence on a single drug will inevitably repeat past experiences with the rapid spread of pyrethroid resistance in malaria vectors. Diversifying the arsenal of systemic insecticides used for mass drug administration would improve this strategy’s sustainability.

Methods

Here, a review was conducted to identify systemic insecticide candidates and consolidate their pharmacokinetic/pharmacodynamic properties. The impact of alternative integrated vector control options and different dosing regimens on malaria transmission reduction are illustrated through mathematical model simulation.

Results

The review identified drugs from four classes commonly used in livestock and companion animals: avermectins, milbemycins, isoxazolines and spinosyns. Simulations predicted that isoxazolines and spinosyns are promising candidates for mass drug administration, as they were predicted to need less frequent application than avermectins and milbemycins to maintain mosquitocidal blood concentrations.

Conclusions

These findings will provide a guide for investigating and applying different systemic insecticides to achieve more effective and sustainable control of malaria transmission.

Reducing malaria burden and accelerating elimination with long-lasting systemic insecticides: a modelling study of three potential use cases

BACKGROUND

While bed nets and insecticide spraying have had significant impact on malaria burden in many endemic regions, outdoor vector feeding and insecticide resistance may ultimately limit their contribution to elimination and control campaigns. Complementary vector control methods such as endectocides or systemic insecticides, where humans or animals are treated with drugs that kill mosquitoes upon ingestion via blood meal, are therefore generating much interest. This work explores the conditions under which long-lasting systemic insecticides would have a substantial impact on transmission and burden.

METHODS

Hypothetical long-lasting systemic insecticides with effective durations ranging from 14 to 90 days are simulated using an individual-based mathematical model of malaria transmission. The impact of systemic insecticides when used to complement existing vector control and drug campaigns is evaluated in three settings-a highly seasonal high-transmission setting, a near-elimination setting with seasonal travel to a high-risk area, and a near-elimination setting in southern Africa.

RESULTS

At 60% coverage, a single round of long-lasting systemic insecticide with effective duration of at least 60 days, distributed at the start of the season alongside a seasonal malaria chemoprevention campaign in a high-transmission setting, results in further burden reduction of 30-90% depending on the sub-populations targeted. In a near-elimination setting where transmission is sustained by seasonal travel to a high-risk area, targeting high-risk travellers with systemic insecticide with effective duration of at least 30 days can result in likely elimination even if intervention coverage is as low as 50%. In near-elimination settings with robust vector control, the addition of a 14-day systemic insecticide alongside an anti-malarial in mass drug administration (MDA) campaigns can decrease the necessary MDA coverage from about 85% to the more easily achievable 65%.

CONCLUSIONS

While further research into the safety profile of systemic insecticides is necessary before deployment, models predict that long-lasting systemic insecticides can play a critical role in reducing burden or eliminating malaria in a range of contexts with different target populations, existing malaria control methods, and transmission intensities. Continued investment in lengthening the duration of systemic insecticides and improving their safety profile is needed for this intervention to achieve its fullest potential.

Would ivermectin for malaria control be beneficial in onchocerciasis-endemic regions?

BACKGROUND

There is accumulating evidence supporting the use of ivermectin as a malaria control tool. Recent findings from the repeat ivermectin mass drug administrations for control of malaria trial demonstrated a reduced incidence of malaria in villages which received repeated ivermectin mass drug administration (MDA; six doses) compared to those who had only one round of ivermectin. Several other studies investigating the benefits of ivermectin for malaria purposes are ongoing/planned.

MAIN TEXT

While ivermectin MDA offers promising perspectives in the fight against malaria, we highlight the added benefits and anticipated challenges of conducting future studies in onchocerciasis-endemic regions, which are confronted with a substantial disease burden including onchocerciasis-associated epilepsy. Increasing the frequency of ivermectin MDA in such places may reduce the burden of both malaria and onchocerciasis, and allow for more entomological investigations on both the Anopheles mosquitoes and the blackflies. Upfront, acceptability and feasibility studies are needed to assess the endorsement by the local populations, as well as the programmatic feasibility of implementing ivermectin MDA several times a year.

CONCLUSIONS

Onchocerciasis-endemic sites would doubly benefit from ivermectin MDA interventions, as these will alleviate onchocerciasis-associated morbidity and mortality, while potentially curbing malaria transmission. Involving onchocerciasis programs and other relevant stakeholders in the malaria/ivermectin research agenda would foster the implementation of pluri-annual MDA in target communities.

Ivermectin Impairs the Development of Sexual and Asexual Stages of Plasmodium falciparum In Vitro

Ivermectin is the drug of choice for many parasitic infections, with more than one billion doses being distributed in onchocerciasis programs. The drug has been put into focus recently by the malaria community because of its potential to kill blood-sucking mosquitoes, thereby reducing malaria transmission. However, the activity of ivermectin against the malaria parasite itself has been only partly investigated. This study aimed to investigate the in vitro activity of ivermectin against asexual and sexual stages of Plasmodium falciparum Both asexual and late-stage gametocytes were incubated with ivermectin and control drugs in vitro The growth-inhibiting effects were assessed for asexual stages of different Plasmodium falciparum laboratory strains and culture-adapted clinical isolates using the histidine-rich protein 2 enzyme-linked immunosorbent assay technique. The effect against stage IV/V gametocytes was evaluated based on ATP quantification. Ivermectin showed activities at nanomolar concentrations against asexual stages (50% inhibitory concentration of ∼100 nM) and stage IV/V gametocytes (500 nM) of P. falciparum Stage-specific assays suggested that ivermectin arrests the parasite cycle at the trophozoite stage. Ivermectin might add a feature to its "wonder drug" properties with activity against asexual stages of the malaria parasite Plasmodium falciparum The observed activities might be difficult to reach with current regimens but will be more relevant with future high-dose regimens under investigation. Further studies should be performed to confirm these results in vitro and in vivo.

Efficacy and risk of harms of repeat ivermectin mass drug administrations for control of malaria (RIMDAMAL): a cluster-randomised trial

BACKGROUND

Ivermectin is widely used in mass drug administrations for controlling neglected parasitic diseases, and can be lethal to malaria vectors that bite treated humans. Therefore, it could be a new tool to reduce plasmodium transmission. We tested the hypothesis that frequently repeated mass administrations of ivermectin to village residents would reduce clinical malaria episodes in children and would be well tolerated with minimal harms.

METHODS

We invited villages (clusters) in Burkina Faso to participate in a single-blind (outcomes assessor), parallel-assignment, two-arm, cluster-randomised trial over the 2015 rainy season. Villages were assigned (1:1) by random draw to either the intervention group or the control group. In both groups, all eligible participants who consented to the treatment and were at least 90 cm in height received single oral doses of ivermectin (150-200 μg/kg) and albendazole (400 mg), and those in the intervention group received five further doses of ivermectin alone at 3-week intervals thereafter over the 18-week treatment phase. The primary outcome was cumulative incidence of uncomplicated malaria episodes over 18 weeks (analysed on a cluster intention-to-treat basis) in an active case detection cohort of children aged 5 years or younger living in the study villages. This trial is registered with ClinicalTrials.gov, number NCT02509481.

FINDINGS

Eight villages agreed to participate, and four were randomly assigned to each group. 2712 participants (1333 [49%] males and 1379 [51%] females; median age 15 years [IQR 6-34]), including 590 children aged 5 years or younger, provided consent and were enrolled between May 22 and July 20, 2015 (except for 77 participants enrolled after these dates because of unavailability before the first mass drug administration, travel into the village during the trial, or birth), with 1447 enrolled into the intervention group and 1265 into the control group. 330 (23%) participants in the intervention group and 233 (18%) in the control group met the exclusion criteria for mass drug administration. Most children in the active case detection cohort were not treated because of height restrictions. 14 (4%) children in the intervention group and 10 (4%) in the control group were lost to follow-up. Cumulative malaria incidence was reduced in the intervention group (648 episodes among 327 children; estimated mean 2·00 episodes per child) compared with the control group (647 episodes among 263 children; 2·49 episodes per child; risk difference -0·49 [95% CI -0·79 to -0·21], p=0·0009, adjusted for sex and clustering). The risk of adverse events among all participants did not differ between groups (45 events [3%] among 1447 participants in the intervention group vs 24 events [2%] among 1265 in the control group; risk ratio 1·63 [1·01 to 2·67]; risk difference 1·21 [0·04 to 2·38], p=0·060), and no adverse reactions were reported.

INTERPRETATION

Frequently repeated mass administrations of ivermectin during the malaria transmission season can reduce malaria episodes among children without significantly increasing harms in the populace.

FUNDING

Bill & Melinda Gates Foundation.

Treatment of pigs with endectocides as a complementary tool for combating malaria transmission by Anopheles farauti (s.s.) in Papua New Guinea

Background

Outdoor, early-biting, zoophagic behaviours by Anopheles farauti (s.s.) can compromise the effectiveness of bed nets for malaria control. In the Western Pacific region, pigs and dogs represent significant alternative blood sources for mosquitoes. Treating these animals with endectocides may impact mosquito survival and complement control measures. This hypothesis was explored using membrane feeding assays (MFAs), direct feeds on treated pigs, pharmacokinetic analyses and a transmission model.

Results

Ivermectin was 375-fold more mosquitocidal than moxidectin (24 h LC₅₀= 17.8 ng/ml vs 6.7 µg/ml) in MFAs, and reduced mosquito fecundity by > 50% at ≥ 5 ng/ml. Treatment of pigs with subcutaneous doses of 0.6 mg/kg ivermectin caused 100% mosquito mortality 8 days after administration. Lethal effects persisted for up to 15 days after administration (75% death within 10 days).

Conclusion

The application of these empirical data to a unique malaria transmission model that used a three-host system (humans, pigs and dogs) predicts that the application of ivermectin will cause a significant reduction in the entomological inoculation rate (EIR = 100 to 0.35). However, this is contingent on local malaria vectors sourcing a significant proportion of their blood meals from pigs. This provides significant insights on the benefits of deploying endectocides alongside long-lasting insecticide-treated nets (LLINs) to address residual malaria transmission.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3392-0) contains supplementary material, which is available to authorized users.

Does artemether-lumefantrine administration affect mosquito olfactory behaviour and fitness?

Background

Artemisinin-based combination therapy (ACT) is the recommended treatment against uncomplicated Plasmodium falciparum infections, and ACT is widely used. It has been shown that gametocytes may be present after ACT and transmission to mosquitoes is still possible. Artemether–lumefantrine (AL) is a broadly used artemisinin-based combination medicine. Here, it is tested whether AL influences behaviour and fitness of Anopheles mosquitoes, which are the main vectors of P. falciparum.

Results

Dual-choice olfactometer and screenhouse experiments showed that skin odour of healthy human individuals obtained before, during and after AL-administration was equally attractive to Anopheles coluzzii and Anopheles gambiae sensu stricto, apart from a small (but significant) increase in mosquito response to skin odour collected 3 weeks after AL-administration. Anopheles coluzzii females fed on parasite-free blood supplemented with AL or on control-blood had similar survival, time until oviposition and number of eggs produced.

Conclusions

Based on the results, AL does not appear to influence malaria transmission through modification of vector mosquito olfactory behaviour or fitness. Extending these studies to Plasmodium-infected individuals and malaria mosquitoes with parasites are needed to further support this conclusion.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2646-9) contains supplementary material, which is available to authorized users.

Antivirus effectiveness of ivermectin on dengue virus type 2 in Aedes albopictus

Background

Dengue fever is the most rapidly spreading mosquito-borne viral disease over the past 50 years, with a 30-fold increase in global incidence. Dengue vector control is a key component for the dengue control strategy, since no absolutely effective vaccine or drug is available yet. However, the rapid rise and spread of mosquito insecticide resistance have become major threats to the efficiency of insecticide-based vector control activities. Thus, innovative vector control tools are badly needed. This study aims to confirm the antivirus effectiveness of ivermectin on dengue virus type 2 (DENV-2) in Aedes albopictus (Skuse, 1894), then to explore its potential use in the combating to the dengue epidemics.

Methods

Aedes albopictus were first infected with DENV-2 in human whole blood, and at the fourth day after infectious blood feeding, they were divided into eight groups. Seven of them were held for six days with access to 0, 2, 4, 8, 16, 32 and 64 ng/ml ivermectin, respectively, and the last one was set as a historical control group, which was stored at -80°C until being detected at the same time with the other groups. Each mosquito was detected using real-time fluorescent RT-PCR kit. DENV-2 RNA concentration (copies/ml) and infection rate in each group were compared.

Results

Both of quantitatively and qualitatively inhibiting effects of ivermectin have been detected in this study. Generally, DENV-2 replicated well in Aedes albopictus without ivermectin intervention, whose virus loads exhibited significantly higher when the mosquitoes were holding from 4 days to 10 days after infectious blood feeding. In contrast, with the treatment of ivermectin, the infection rate was reduced by as much as 49.63%. The regression equation between infection rates (Y₂) and ivermectin concentration log₂ values (X₂) was obtained as Y₂ = 91.41–7.21*X₂ with R² = 0.89.

Conclusion

Ivermectin can directly or indirectly inhibit DENV-2 multiplication in Aedes albopictus. Moreover, the actual concentration for application in zooprophylaxis needs to be confirmed in the further field trials.

Dengue fever is one of neglected vector-borne tropical diseases with a 30-fold increase in global incidence recently. In 2012, World Health Organization set a goal to reduce dengue mortality by at least 50% by 2020. Being faced with more challenges in the dengue control programs, such as the increase of dengue outbreaks, lacking absolutely effective vaccine, rise of vector insecticide resistance and so on; innovative vector control tools are urgently needed for current control programs on dengue fever. To find a new avenue in vector control, we for the first time assessed the inhibiting effectiveness of ivermectin on dengue virus type 2 (DENV-2) inside Aedes mosquitoes. We found that about 80% Aedes albopictus mosquitoes were effectively infected with DENV-2 without treatment of ivermectin. But in the groups of ivermectin treatment, the infection rate of DENV-2 and the median of virus loads were significantly reduced by up to 49.63% and 99.99%, respectively. Both quantitatively and qualitatively inhibiting effects of ivermectin were detected. We found out that ivermectin was able to effectively inhibit the DENV-2 multiplication in Aedes albopictus, which may gave us a hint that using ivermectin in some control programs as a zooprophylaxis to block dengue epidemic through inhibiting DENV-2 in field Aedes mosquitoes.

Mesocosm experiments reveal the impact of mosquito control measures on malaria vector life history and population dynamics

The impact of control measures on mosquito vector fitness and demography is usually estimated from bioassays or indirect variables in the field. Whilst indicative, neither approach is sufficient to quantify the potentially complex response of mosquito populations to combined interventions. Here, large replicated mesocosms were used to measure the population-level response of the malaria vector Anopheles arabiensis to long-lasting insecticidal nets (LLINs) when used in isolation, or combined with insecticidal eave louvers (EL), or treatment of cattle with the endectocide Ivermectin (IM). State-space models (SSM) were fit to these experimental data, revealing that LLIN introduction reduced adult mosquito survival by 91% but allowed population persistence. ELs provided no additional benefit, but IM reduced mosquito fecundity by 59% and nearly eliminated all populations when combined with LLINs. This highlights the value of IM for integrated vector control, and mesocosm population experiments combined with SSM for identifying optimal combinations for vector population elimination.

Repurposing isoxazoline veterinary drugs for control of vector-borne human diseases

Isoxazolines are oral insecticidal drugs currently licensed for ectoparasite control in companion animals. Here we propose their use in humans for the reduction of vector-borne disease incidence. Fluralaner and afoxolaner rapidly killed Anopheles, Aedes, and Culex mosquitoes and Phlebotomus sand flies after feeding on a drug-supplemented blood meal, with IC50 values ranging from 33 to 575 nM, and were fully active against strains with preexisting resistance to common insecticides. Based on allometric scaling of preclinical pharmacokinetics data, we predict that a single human median dose of 260 mg (IQR, 177-407 mg) for afoxolaner, or 410 mg (IQR, 278-648 mg) for fluralaner, could provide an insecticidal effect lasting 50-90 days against mosquitoes and Phlebotomus sand flies. Computational modeling showed that seasonal mass drug administration of such a single dose to a fraction of a regional population would dramatically reduce clinical cases of Zika and malaria in endemic settings. Isoxazolines therefore represent a promising new component of drug-based vector control.

Targeting cattle for malaria elimination: marked reduction of Anopheles arabiensis survival for over six months using a slow-release ivermectin implant formulation

Background

Mosquitoes that feed on animals can survive and mediate residual transmission of malaria even after most humans have been protected with insecticidal bednets or indoor residual sprays. Ivermectin is a widely-used drug for treating parasites of humans and animals that is also insecticidal, killing mosquitoes that feed on treated subjects. Mass administration of ivermectin to livestock could be particularly useful for tackling residual malaria transmission by zoophagic vectors that evade human-centred approaches. Ivermectin comes from a different chemical class to active ingredients currently used to treat bednets or spray houses, so it also has potential for mitigating against emergence of insecticide resistance. However, the duration of insecticidal activity obtained with ivermectin is critical to its effectiveness and affordability.

Results

A slow-release formulation for ivermectin was implanted into cattle, causing 40 weeks of increased mortality among Anopheles arabiensis that fed on them. For this zoophagic vector of residual malaria transmission across much of Africa, the proportion surviving three days after feeding (typical mean duration of a gonotrophic cycle in field populations) was approximately halved for 25 weeks.

Conclusions

This implantable ivermectin formulation delivers stable and sustained insecticidal activity for approximately 6 months. Residual malaria transmission by zoophagic vectors could be suppressed by targeting livestock with this long-lasting formulation, which would be impractical or unacceptable for mass treatment of human populations.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2872-y) contains supplementary material, which is available to authorized users.

Safety and mosquitocidal efficacy of high-dose ivermectin when co-administered with dihydroartemisinin-piperaquine in Kenyan adults with uncomplicated malaria (IVERMAL): a randomised, double-blind, placebo-controlled trial

BACKGROUND

Ivermectin is being considered for mass drug administration for malaria due to its ability to kill mosquitoes feeding on recently treated individuals. However, standard, single doses of 150-200 μg/kg used for onchocerciasis and lymphatic filariasis have a short-lived mosquitocidal effect (<7 days). Because ivermectin is well tolerated up to 2000 μg/kg, we aimed to establish the safety, tolerability, and mosquitocidal efficacy of 3 day courses of high-dose ivermectin, co-administered with a standard malaria treatment.

METHODS

We did a randomised, double-blind, placebo-controlled, superiority trial at the Jaramogi Oginga Odinga Teaching and Referral Hospital (Kisumu, Kenya). Adults (aged 18-50 years) were eligible if they had confirmed symptomatic uncomplicated Plasmodium falciparum malaria and agreed to the follow-up schedule. Participants were randomly assigned (1:1:1) using sealed envelopes, stratified by sex and body-mass index (men: <21 vs ≥21 kg/m²; women: <23 vs ≥23 kg/m²), with permuted blocks of three, to receive 3 days of ivermectin 300 μg/kg per day, ivermectin 600 μg/kg per day, or placebo, all co-administered with 3 days of dihydroartemisinin-piperaquine. Blood of patients taken on post-treatment days 0, 2 + 4 h, 7, 10, 14, 21, and 28 was fed to laboratory-reared Anopheles gambiae sensu stricto mosquitoes, and mosquito survival was assessed daily for 28 days after feeding. The primary outcome was 14-day cumulative mortality of mosquitoes fed 7 days after ivermectin treatment (from participants who received at least one dose of study medication). The study is registered with ClinicalTrials.gov, number NCT02511353.

FINDINGS

Between July 20, 2015, and May 7, 2016, 741 adults with malaria were assessed for eligibility, of whom 141 were randomly assigned to receive ivermectin 600 μg/kg per day (n=47), ivermectin 300 μg/kg per day (n=48), or placebo (n=46). 128 patients (91%) attended the primary outcome visit 7 days post treatment. Compared with placebo, ivermectin was associated with higher 14 day post-feeding mosquito mortality when fed on blood taken 7 days post treatment (ivermectin 600 μg/kg per day risk ratio [RR] 2·26, 95% CI 1·93-2·65, p<0·0001; hazard ratio [HR] 6·32, 4·61-8·67, p<0·0001; ivermectin 300 μg/kg per day RR 2·18, 1·86-2·57, p<0·0001; HR 4·21, 3·06-5·79, p<0·0001). Mosquito mortality remained significantly increased 28 days post treatment (ivermectin 600 μg/kg per day RR 1·23, 1·01-1·50, p=0·0374; and ivermectin 300 μg/kg per day 1·21, 1·01-1·44, p=0·0337). Five (11%) of 45 patients receiving ivermectin 600 μg/kg per day, two (4%) of 48 patients receiving ivermectin 300 μg/kg per day, and none of 46 patients receiving placebo had one or more treatment-related adverse events.

INTERPRETATION

Ivermectin at both doses assessed was well tolerated and reduced mosquito survival for at least 28 days after treatment. Ivermectin 300 μg/kg per day for 3 days provided a good balance between efficacy and tolerability, and this drug shows promise as a potential new tool for malaria elimination.

FUNDING

Malaria Eradication Scientific Alliance (MESA) and US Centers for Disease Control and Prevention (CDC).

Multidrug-resistant malaria and the impact of mass drug administration

Based on the emergence and spread throughout the Greater Mekong Subregion (GMS) of multiple artemisinin-resistant lineages, the prevalence of multidrug resistance leading to high rates of artemisinin-based combination treatment failure in parts of the GMS, and the declining malaria burden in the region, the World Health Organization has recommended complete elimination of falciparum malaria from the GMS. Mass drug administration (MDA) is being piloted as one elimination intervention to be employed as part of this effort. However, concerns remain as to whether MDA might exacerbate the already prevalent problem of multidrug resistance in the region. In this review, we briefly discuss challenges of MDA, the use of MDA in the context of multidrug-resistant malaria, and the potential of different drug combinations and drug-based elimination strategies for mitigating the emergence and spread of resistance.

Promising approach to reducing Malaria transmission by ivermectin: Sporontocidal effect against Plasmodium vivax in the South American vectors Anopheles aquasalis and Anopheles darlingi

Background

The mosquito resistance to the insecticides threatens malaria control efforts, potentially becoming a major public health issue. Alternative methods like ivermectin (IVM) administration to humans has been suggested as a possible vector control to reduce Plasmodium transmission. Anopheles aquasalis and Anopheles darlingi are competent vectors for Plasmodium vivax, and they have been responsible for various malaria outbreaks in the coast of Brazil and the Amazon Region of South America.

Methods

To determine the IVM susceptibility against P. vivax in An. aquasalis and An. darlingi, ivermectin were mixed in P. vivax infected blood: (1) Powdered IVM at four concentrations (0, 5, 10, 20 or 40 ng/mL). (2) Plasma (0 hours, 4 hours, 1 day, 5, 10 and 14 days) was collected from healthy volunteers after to administer a single oral dose of IVM (200 μg/kg) (3) Mosquitoes infected with P. vivax and after 4 days was provided with IVM plasma collected 4 hours post-treatment (4) P. vivax-infected patients were treated with various combinations of IVM, chloroquine, and primaquine and plasma or whole blood was collected at 4 hours. Seven days after the infective blood meal, mosquitoes were dissected to evaluate oocyst presence. Additionally, the ex vivo effects of IVM against asexual blood-stage P. vivax was evaluated.

Results

IVM significantly reduced the prevalence of An. aquasalis that developed oocysts in 10 to 40 ng/mL pIVM concentrations and plasma 4 hours, 1 day and 5 days. In An. darlingi to 4 hours and 1 day. The An. aquasalis mortality was expressively increased in pIVM (40ng/mL) and plasma 4 hours, 1, 5 10 and 14 days post-intake drug and in An. darlingi only to 4 hours and 1 day. The double fed meal with mIVM by the mosquitoes has a considerable impact on the proportion of infected mosquitoes for 7 days post-feeding. The oocyst infection prevalence and intensity were notably reduced when mosquitoes ingested blood from P. vivax patients that ingested IVM+CQ, PQ+CQ and IVM+PQ+CQ. P. vivax asexual development was considerably inhibited by mIVM at four-fold dilutions.

Conclusion

In conclusion, whole blood spiked with IVM reduced the infection rate of P. vivax in An. aquasalis and An. darlingi, and increased the mortality of mosquitoes. Plasma from healthy volunteers after IVM administration affect asexual P. vivax development. These findings support that ivermectin may be used to decrease P. vivax transmission.

Malaria is one of the most important infectious diseases in the world with hundreds of millions of new cases every year. The disease is caused by parasites of the genus Plasmodium where Plasmodium vivax represent most of the cases in the Americas. Current strategies to combat malaria transmission are being implemented; however, widespread insecticide resistance in vectors threatens the effectiveness of vector control programs. Ivermectin (IVM) has arisen as a new potential tool to be added to these programs as it has mosquito-lethal and sporontocidal properties making it a promising transmission reduction drug. Plasmodium vivax was drawn from patients, mixed with powdered IVM and metabolized IVM in plasma collected from healthy volunteers receiving IVM, and fed to mosquitoes via membrane feeding. Powdered and metabolized IVM interrupt P. vivax transmission, reducing oocyst infection and intensity rate of two South American malaria vectors An. aquasalis and An. darlingi. We also demonstrate the effect of IVM on asexual stages development of P. vivax, providing evidence that IVM may affect different parasite life cycle stages. Our findings place IVM as a strong candidate for malaria transmission reducing interventions.

Modern Vector Control

The rapid spread of mosquito resistance to currently available insecticides, and the current lack of an efficacious malaria vaccine are among many challenges that affect large-scale efforts for malaria control. As goals of malaria elimination and eradication are put forth, new vector-control paradigms and tools and/or further optimization of current vector-control products are required to meet public health demands. Vector control remains the most effective measure to prevent malaria transmission and present gains against malaria mortality and morbidity may be maintained as long as vector-intervention strategies are sustained and adapted to underlying vector-related transmission dynamics. The following provides a brief overview of vector-control strategies and tools either in use or under development and evaluation that are intended to exploit key entomological parameters toward driving down transmission.

Expanding the Vector Control Toolbox for Malaria Elimination: A Systematic Review of the Evidence

BACKGROUND

Additional vector control tools (VCTs) are needed to supplement insecticide-treated nets (ITNs) and indoor residual spraying (IRS) to achieve malaria elimination in many settings. To identify options for expanding the malaria vector control toolbox, we conducted a systematic review of the availability and quality of the evidence for 21 malaria VCTs, excluding ITNs and IRS.

METHODS

Six electronic databases and grey literature sources were searched from January 1, 1980 to September 28, 2015 to identify systematic reviews, Phase I-IV studies, and observational studies that measured the effect of malaria VCTs on epidemiological or entomological outcomes across any age groups in all malaria-endemic settings. Eligible studies were summarized qualitatively, with quality and risk of bias assessments undertaken where possible. Of 17,912 studies screened, 155 were eligible for inclusion and were included in a qualitative synthesis.

RESULTS

Across the 21 VCTs, we found considerable heterogeneity in the volume and quality of evidence, with 7 VCTs currently supported by at least one Phase III community-level evaluation measuring parasitologically confirmed malaria incidence or infection prevalence (insecticide-treated clothing and blankets, insecticide-treated hammocks, insecticide-treated livestock, larval source management (LSM), mosquito-proofed housing, spatial repellents, and topical repellents). The remaining VCTs were supported by one or more Phase II (n=13) or Phase I evaluation (n=1). Overall the quality of the evidence base remains greatest for LSM and topical repellents, relative to the other VCTs evaluated, although existing evidence indicates that topical repellents are unlikely to provide effective population-level protection against malaria.

CONCLUSIONS

Despite substantial gaps in the supporting evidence, several VCTs may be promising supplements to ITNs and IRS in appropriate settings. Strengthening operational capacity and research to implement underutilized VCTs, such as LSM and mosquito-proofed housing, using an adaptive, learning-by-doing approach, while expanding the evidence base for promising supplementary VCTs that are locally tailored, should be considered central to global malaria elimination efforts.

What does not kill it makes it weaker: effects of sub-lethal concentrations of ivermectin on the locomotor activity of Anopheles aquasalis

Background

Malaria remains a major public health concern. Vector control measures based solely on insecticide treated nets (ITNs) and indoor residual spraying (IRS) have demonstrated not to be feasible for malaria elimination. It has been shown that ivermectin affects several aspects of Anopheles species biology. Along the Latin American seacoast, Anopheles aquasalis Curry plays an important role in malaria transmission. The observation of mosquitoes locomotor activity under laboratory conditions can reveal details of their daily activity rhythms, which is controlled by an endogenous circadian clock that seems to be influenced by external signals, such as light and temperature. In this study, we assessed basal locomotor activity and the effects of ivermectin on locomotor activity of the American malaria vector, An. aquasalis.

Methods

Adult females of Anopheles aquasalis used in experiments were three to five days post-emergence. Blood from one single subject was used to provide mosquito meals by membrane feeding assays. Powdered ivermectin compound was used to achieve different concentrations of drug as previously described. Fully engorged mosquitoes were individually placed into glass tubes and provided with 10% sucrose. Each tube was placed into a Locomotor Activity Monitor (LAM). The LAMs were kept inside an incubator under a constant temperature and a 12:12 h light:dark cycle. The average locomotor activity was calculated as the mean number of movements performed per mosquito in the period considered. Intervals of time assessed were adapted from a previous study. One-way ANOVA tests were performed in order to compare means between groups. Additionally, Dunnett’s method was used for post-hoc pairwise means comparisons between each group and control. Stata software version 13 was used for the analysis.

Results

Anopheles aquasalis showed a nocturnal and bimodal pattern for mosquitoes fed both control blood meals and sub-lethal concentrations of ivermectin. In this species, activity peaks occurred at the beginning of the photophase and scotophase in the control group. The nocturnal activity is evident and higher just after the evening peak and maintains basal levels of locomotion throughout the scotophase. In the entire group analysis, locomotor activity means of experimental sets were significantly lower than control for each period of time evaluated. In the survival group, the locomotor activity means of all treatment sets were lower than control mosquitoes for all intervals of time when both the whole period and scotophase were assessed. When the middle of scotophase was evaluated, means were significantly lower for LC₁₅ and LC₂₅, but not LC₅. For the beginning of photophase period, significant differences were detected only between control and LC₅. When both the photophase and scotophase were assessed alone, no significant differences were found. Mean locomotor activity was significantly lower for dead group when compared to survival group for all experimental sets when whole period, photophase, and scotophase were assessed.

Conclusions

Ivermectin seems to decrease locomotor activity of An. aquasalis at sub-lethal concentrations. The effects on locomotor activity increase according at higher ivermectin concentrations and are most evident during the whole scotophase as well as in the beginning and in the end of this phase, and sub-lethal effects may still be observed in the photophase. Findings presented in this study demonstrate that sub-lethal ivermectin effects reduce mosquito locomotor activity, which could diminish vectorial capacity and therefore the malaria transmission.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2563-0) contains supplementary material, which is available to authorized users.

Cytochrome P450/ABC transporter inhibition simultaneously enhances ivermectin pharmacokinetics in the mammal host and pharmacodynamics in Anopheles gambiae

Mass administration of endectocides, drugs that kill blood-feeding arthropods, has been proposed as a complementary strategy to reduce malaria transmission. Ivermectin is one of the leading candidates given its excellent safety profile. Here we provide proof that the effect of ivermectin can be boosted at two different levels by drugs inhibiting the cytochrome or ABC transporter in the mammal host and the target mosquitoes. Using a mini-pig model, we show that drug-mediated cytochrome P450/ABC transporter inhibition results in a 3-fold increase in the time ivermectin remains above mosquito-killing concentrations. In contrast, P450/ABC transporter induction with rifampicin markedly impaired ivermectin absorption. The same ketoconazole-mediated cytochrome/ABC transporter inhibition also occurs outside the mammal host and enhances the mortality of Anopheles gambiae. This was proven by using the samples from the mini-pig experiments to conduct an ex-vivo synergistic bioassay by membrane-feeding Anopheles mosquitoes. Inhibiting the same cytochrome/xenobiotic pump complex in two different organisms to simultaneously boost the pharmacokinetic and pharmacodynamic activity of a drug is a novel concept that could be applied to other systems. Although the lack of a dose-response effect in the synergistic bioassay warrants further exploration, our study may have broad implications for the control of parasitic and vector-borne diseases.