High susceptibility of wild Anopheles funestus to infection with natural Plasmodium falciparum gametocytes using membrane feeding assays

Infectivity of symptomatic Plasmodium vivax cases to different generations of wild-caught and laboratory-adapted Anopheles arabiensis using a membrane feeding assay, Ethiopia

When measuring human to mosquito transmission of Plasmodium spp., laboratory-adapted (colony) mosquitoes can be utilized. To connect transmission studies to the local epidemiology, it can be important to comprehend the relationship between infectivity in laboratory-adapted (colony) and wild-caught (wild) mosquitoes of the same species. Microscopically confirmed Plasmodium vivax cases were recruited from health facilities in Arba Minch town, and a nested polymerase chain reaction (nPCR) was used for subsequent confirmation. We performed paired membrane-feeding assays using colony An. arabiensis and three generations of wild origin An. arabiensis. Anopheles arabiensis aged 3-6 days were fed after being starved for 8-14 h. Microscopically, the oocyst development was evaluated at day 7 after feeding. Circumsporozoite proteins (CSPs) assay was carried out by enzyme-linked immunosorbent assay (ELISA). In 19 paired feeding experiments, the feeding efficiency was more than doubled in colony (median: 62.5%; interquartile range, IQR: 35-78%) than in wild mosquitoes (median: 28.5%; IQR: 17.5-40%; P < 0.001). Among the 19 P. vivax gametocyte-positive blood samples, 63.2% (n = 12) were infective to wild An. arabiensis and 73.7% (n = 14) were infective to colony An. arabiensis. The median infection rate was twice as high (26%) in the colony than in the wild (13%) An. arabiensis, although the difference was marginally insignificant (P = 0.06). Although the observed difference was not statistically significant (P = 0.19), the median number of oocysts per midgut was more than twice as high (17.8/midgut) in colony than in wild (7.2/midgut) An. arabiensis. The median feeding efficiency was 26.5% (IQR: 18-37%) in F1, 29.3% (IQR: 28-40%) in F2 and 31.2% (IQR: 30-37%) in F3 generations of wild An. arabiensis. Also, no significant difference was observed in oocyst infection rate and load between generations of wild An. arabiensis. CSP rate of P. vivax was 3.1% (3/97; 95% CI: 0.6-8.8%) in wild and 3.6% (3/84; 95% CI: 0.7-10.1%) in colony An. arabiensis. The results of the present study revealed that oocyst infection and load/midgut, and CSP rate were roughly comparable, indicating that colony mosquitoes can be employed for infectivity studies, while larger sample sizes may be necessary in future studies.

Molecular identification and wing variations among malaria vectors in Akure North Local Government Area, Nigeria

Members of the Anopheles gambiae complex and Anopheles funestus group are significant vectors of the malaria parasite Plasmodium species in the Afro-tropical region of the world. Molecular identification and variation in the wing were studied among female An. Gambiae complex and An. funestus group, to investigate morphological variations in the wing of local vectors populations of adult female mosquitoes found in five different locations in Akure North Local Government Area of Ondo State (Oba-Ile, Igoba, Isinigbo, Ita-Ogbolu and Iju). The variations in the wing character were found in the 3rd main dark spot area (Pre-apical dark spot-character 8) on the coastal region (Vein region I) of Anopheles gambiae complex wing; with two types (A and B) of wings identified with An. gambiae complex in the study area. Molecular study shows that all the wing type A are Anopheles gambiae s.s., they represent 53.39% of the total An. gambiae complex in the study area. Some of the Anopheles gambiae s.s. (28.30%) and all An. arabiensis (18.30%) were found with wing type B. Among 750 individual Anopheles mosquito species identified using Polymerase Chain Reaction (PCR method), 433 samples representing 57.73% were An. gambiae s.s. while 97 (12.93%) samples were An. arabiensis. Anopheles leesoni was the only member of the An. funestus group identified in the study area. Anopheles leesoni mosquitoes identified in the study location were 182, representing 24.27% of the total Anopheles mosquito species identified using the molecular method. Anopheles gambiae s.s., An. arabiensis, and An. leesoni are only Anopheles mosquito species responsible for malaria transmission in the study area. Anopheles leesoni was the only member of the An. funestus group identified in the study area.

Knowledge, Attitude, and Practices (KAP) of Human Populations towards Malaria Control in Four Ecoepidemiological Settings in Cameroon

Malaria remains a major public health problem in Cameroon. Critical steps to improve disease control include assessing human population adherence to vector control interventions, especially in areas with different cultural backgrounds. The present study seeks to assess the knowledge, attitude, and practices (KAP) of populations towards malaria prevention in four ecoepidemiological settings in Cameroon. A cross-sectional malaria KAP survey was conducted from August to September 2019 in households of the localities of Kaélé, Tibati, Bertoua, and Santchou. A semistructured questionnaire was administered to randomly selected households in the localities. Data recorded were analysed using SPSS v. 20 and MedCalc v14.8.1. A total of 739 households were surveyed. The majority of participants had a secondary level of education (48.71%). A substantial number of participants (over 90%) in all the localities were able to make an accurate association between malaria and mosquito bites. The main sources of information for community members were television sets in Santchou and Tibati and interpersonal conversations in Bertoua and Kaélé. Mosquito nets were the most commonly used protective measure against malaria, and the majority of nets in households came from the free-of-charge mass distribution campaigns organized by the government. Participants with secondary and higher levels of education were more aware of good practices towards malaria control compared to those with a primary level of education. The study revealed that populations' KAP differed according to localities and culture. More sensitization and education need to be done to improve adherence to prevention programs.

Investigation of dengue-malaria coinfection among febrile patients consulting at Ngaoundere Regional Hospital, Cameroon

This study aimed at evaluating the seroprevalence of dengue among malarious patients consulting at the Ngaoundere Regional Hospital. During 2 months and a half, 174 participants were recruited and their blood samples were screened for Plasmodium spp and then for Dengue virus (DENV) infection using rapid diagnostic tests. Also, hematological asparameters were measured using a hematology autoanalyzer. Among patients tested, 134 (77.01%) were malaria-positive, and 12/134 (8.95%) were coinfected. In this population, 8/12 (66.67%) were only anti-DENV IgM-positive, 3/12 (25%) were both NS1 and anti-DENV IgM positive, and 1/12 (8.33%) were anti-DENV IgG-positive. Furthermore, women were more affected (58.3%) than men (41.7%). The most affected age groups were young people aged less than or equal to 15 years (33.3%) and adults aged between 30 and 45 years (33.3%). A significant association (p < .05; odds ratio [OR] = 5.16) was found between the age range (30-45) and dengue-malaria coinfection. Similarly, we noted a significant association between the coinfection, and joint pain (p < .05; OR = 6.15), fatigue (p < .01; OR = 5.74), and chills (p < .05; OR = 0). Analysis of hematologic parameters showed a significant decrease (p < .001) in platelets in coinfected patients compared with monoinfected patients. In conclusion, dengue-malaria coinfection is a reality in Ngaoundere city and associated with the appearance of clinical features which predict the disease severity.

Transcriptomic response of Anopheles gambiae sensu stricto mosquito larvae to Curry tree (Murraya koenigii) phytochemicals

BACKGROUND

Insect growth regulators (IGRs) can control insect vector populations by disrupting growth and development in juvenile stages of the vectors. We previously identified and described the curry tree (Murraya koenigii (L.) Spreng) phytochemical leaf extract composition (neplanocin A, 3-(1-naphthyl)-L-alanine, lumiflavine, terezine C, agelaspongin and murrayazolinol), which disrupted growth and development in Anopheles gambiae sensu stricto mosquito larvae by inducing morphogenetic abnormalities, reducing locomotion and delaying pupation in the mosquito. Here, we attempted to establish the transcriptional process in the larvae that underpins these phenotypes in the mosquito.

METHODS

We first exposed third-fourth instar larvae of the mosquito to the leaf extract and consequently the inherent phytochemicals (and corresponding non-exposed controls) in two independent biological replicates. We collected the larvae for our experiments sampled 24 h before peak pupation, which was 7 and 18 days post-exposure for controls and exposed larvae, respectively. The differences in duration to peak pupation were due to extract-induced growth delay in the larvae. The two study groups (exposed vs control) were consequently not age-matched. We then sequentially (i) isolated RNA (whole larvae) from each replicate treatment, (ii) sequenced the RNA on Illumina HiSeq platform, (iii) performed differential bioinformatics analyses between libraries (exposed vs control) and (iv) independently validated the transcriptome expression profiles through RT-qPCR.

RESULTS

Our analyses revealed significant induction of transcripts predominantly associated with hard cuticular proteins, juvenile hormone esterases, immunity and detoxification in the larvae samples exposed to the extract relative to the non-exposed control samples. Our analysis also revealed alteration of pathways functionally associated with putrescine metabolism and structural constituents of the cuticle in the extract-exposed larvae relative to the non-exposed control, putatively linked to the exoskeleton and immune response in the larvae. The extract-exposed larvae also appeared to have suppressed pathways functionally associated with molting, cell division and growth in the larvae. However, given the age mismatch between the extract-exposed and non-exposed larvae, we can attribute the modulation of innate immune, detoxification, cuticular and associated transcripts and pathways we observed to effects of age differences among the larvae samples (exposed vs control) and to exposures of the larvae to the extract.

CONCLUSIONS

The exposure treatment appears to disrupt cuticular development, immune response and oxidative stress pathways in Anopheles gambiae s.s larvae. These pathways can potentially be targeted in development of more efficacious curry tree phytochemical-based IGRs against An. gambiae s.s mosquito larvae.

Comparison of infectivity of Plasmodium vivax to wild-caught and laboratory-adapted (colonized) Anopheles arabiensis mosquitoes in Ethiopia

BACKGROUND

Mosquito-feeding assays that assess transmission of Plasmodium from man-to-mosquito typically use laboratory mosquito colonies. The microbiome and genetic background of local mosquitoes may be different and influence Plasmodium transmission efficiency. In order to interpret transmission studies to the local epidemiology, it is therefore crucial to understand the relationship between infectivity in laboratory-adapted and local mosquitoes.

METHODS

We assessed infectivity of Plasmodium vivax-infected patients from Adama, Ethiopia, using laboratory-adapted (colony) and wild-caught (wild) mosquitoes raised from larval collections in paired feeding experiments. Feeding assays used 4-6 day-old female Anopheles arabiensis mosquitoes after starvation for 12 h (colony) and 18 h (wild). Oocyst development was assessed microscopically 7 days post-feeding. Wild mosquitoes were identified morphologically and confirmed by genotyping. Asexual parasites and gametocytes were quantified in donor blood by microscopy.

RESULTS

In 36 paired experiments (25 P. vivax infections and 11 co-infections with P. falciparum), feeding efficiency was higher in colony (median: 62.5%; interquartile range, IQR: 47.0-79.0%) compared to wild mosquitoes (median: 27.8%; IQR: 17.0-38.0%; Z = 5.02; P < 0.001). Plasmodium vivax from infectious individuals (51.6%, 16/31) infected a median of 55.0% (IQR: 6.7-85.7%; range: 5.5-96.7%; n = 14) of the colony and 52.7% (IQR: 20.0-80.0%; range: 3.2-95.0%; n = 14) of the wild mosquitoes. A strong association (ρ(16) = 0.819; P < 0.001) was observed between the proportion of infected wild and colony mosquitoes. A positive association was detected between microscopically detected gametocytes and the proportion of infected colony (ρ(31) = 0.452; P = 0.011) and wild (ρ(31) = 0.386; P = 0.032) mosquitoes.

CONCLUSIONS

Infectivity assessments with colony and wild mosquitoes yielded similar infection results. This finding supports the use of colony mosquitoes for assessments of the infectious reservoir for malaria in this setting whilst acknowledging the importance of mosquito factors influencing sporogonic development of Plasmodium parasites.

Review of malaria situation in Cameroon: technical viewpoint on challenges and prospects for disease elimination

Malaria still has a devastating impact on public health and welfare in Cameroon. Despite the increasing number of studies conducted on disease prevalence, transmission patterns or treatment, there are to date, not enough studies summarising findings from previous works in order to identify gaps in knowledge and areas of interest where further evidence is needed to drive malaria elimination efforts. The present study seeks to address these gaps by providing a review of studies conducted so far on malaria in Cameroon since the 1940s to date. Over 250 scientific publications were consulted for this purpose. Although there has been increased scale-up of vector control interventions which significantly reduced the morbidity and mortality to malaria across the country from a prevalence of 41% of the population reporting at least one malaria case episode in 2000 to a prevalence of 24% in 2017, the situation is not yet under control. There is a high variability in disease endemicity between epidemiological settings with prevalence of Plasmodium parasitaemia varying from 7 to 85% in children aged 6 months to 15 years after long-lasting insecticidal nets (LLINs) scale-up. Four species of Plasmodium have been recorded across the country: Plasmodium falciparum, P. malariae, P. ovale and P. vivax. Several primate-infecting Plasmodium spp. are also circulating in Cameroon. A decline of artemisinin-based combinations therapeutic efficacy from 97% in 2006 to 90% in 2016 have been reported. Several mutations in the P. falciparum chloroquine resistance (Pfcrt) and P. falciparum multidrug resistance 1 (Pfmdr1) genes conferring resistance to either 4-amino-quinoleine, mefloquine, halofanthrine and quinine have been documented. Mutations in the Pfdhfr and Pfdhps genes involved in sulfadoxine-pyrimethamine are also on the rise. No mutation associated with artemisinin resistance has been recorded. Sixteen anopheline species contribute to malaria parasite transmission with six recognized as major vectors: An. gambiae, An. coluzzii, An. arabiensis, An. funestus, An. nili and An. moucheti. Studies conducted so far, indicated rapid expansion of DDT, pyrethroid and carbamate resistance in An. gambiae, An. coluzzii, An. arabiensis and An. funestus threatening the performance of LLINs. This review highlights the complex situation of malaria in Cameroon and the need to urgently implement and reinforce integrated control strategies in different epidemiological settings, as part of the substantial efforts to consolidate gains and advance towards malaria elimination in the country.

Exploring the impact of glutathione S-transferase (GST)-based metabolic resistance to insecticide on vector competence of Anopheles funestus for Plasmodium falciparum

Background: Malaria control heavily relies on insecticide-based interventions against mosquito vectors. However, the increasing spread of insecticide resistance is a major threat. The extent to which such resistance, notably metabolic resistance, influences the development of the Plasmodium parasite and its impact on overall malaria transmission remains poorly characterized. Here, we investigated whether glutathione S-transferase-based resistance could influence Plasmodium falciparum development in Anopheles funestus.

Methods: Anopheles funestus females were infected with P. falciparum gametocytes and midguts were dissected at day 7 post infection for detection/quantification of oocysts. Infection parameters were compared between individuals with different L119F-GSTe2 genotypes, and the polymorphism of the GSTe2 gene was analyzed in infected and uninfected mosquito groups.

Results: Overall, 403 An. funestus  mosquitoes were dissected and genotyped. The frequency of the L119F-GSTe2 resistance allele was significantly higher in non-infected (55.88%) compared to infected (40.99%) mosquitoes (Fisher's exact test, P<0.0001). Prevalence of infection was significantly higher in heterozygous and homozygous susceptible genotypes (P<0.001). However, homozygous resistant and heterozygous mosquitoes exhibited significantly higher infection intensity (P<0.01). No association was observed between the GSTe2 polymorphism and the infection status of mosquitoes.

Conclusion: Altogether, these results suggest that GSTe2-based metabolic resistance may affect the vectorial competence of resistant An. funestus mosquitoes to P. falciparum infection, by possibly increasing its permissiveness to Plasmodium infection.

Exploring the impact of glutathione S-transferase (GST)-based metabolic resistance to insecticide on vector competence of Anopheles funestus for Plasmodium falciparum

Background:Malaria control heavily relies on insecticide-based interventions against mosquito vectors. However, the increasing spread of insecticide resistance is a major threat. The extent to which such resistance, notably metabolic resistance, interferes with the development of thePlasmodiumparasite and its impact on overall malaria transmission remains poorly characterized. Here, we investigated whether glutathione S-transferase-based resistance could influencePlasmodium falciparumdevelopment inAnopheles funestus.Methods:Anopheles funestusfemales were infected withP. falciparumgametocytes and midguts were dissected at day 7 post infection for detection/quantification of oocysts. Infection parameters were compared between individual with different L119F-GSTe2 genotypes, and the polymorphism of the GSTe2 gene was analyzed in infected and uninfected mosquito groups.Results:Overall, 403 mosquitoes were dissected and genotyped. The frequency of the L119F-GSTe2 resistance allele was significantly higher in non-infected (55.88%) compared to infected (40.99%) mosquitoes (Fisher's exact test, P<0.0001). Prevalence of infection was significantly higher in heterozygous and homozygous susceptible genotypes (P<0.001). However, homozygous resistant and heterozygous mosquitoes exhibited significantly higher infection intensity (P<0.01). No association was observed between the GSTe2 polymorphism and the infection status of mosquitoes.Conclusion:Altogether, these results suggest that GSTe2-based metabolic resistance may affect the vectorial competence of resistantAn. funestusmosquitoes toP. falciparuminfection, by increasing its permissiveness toPlasmodiuminfection.

Overexpression of Two Members of D7 Salivary Genes Family is Associated with Pyrethroid Resistance in the Malaria Vector Anopheles Funestus s.s. but Not in Anopheles Gambiae in Cameroon

D7 family proteins are among the most expressed salivary proteins in mosquitoes. They facilitate blood meal intake of the mosquito by scavenging host amines that induce vasoconstriction, platelet aggregation and pain. Despite this important role, little information is available on the impact of insecticide resistance on the regulation of D7 proteins and consequently on the blood feeding success. In this study, real-time quantitative polymerase chain reaction (qPCR) analyses were performed to investigate how pyrethroid resistance could influence the expression of genes encoding D7 family proteins in Anopheles gambiae and Anopheles funestus s.s. mosquitoes from Elon in the Central Cameroon. Out of 328 collected mosquitoes, 256 were identified as An. funestus sl and 64 as An. gambiae sl. Within the An. funestus group, An. funestus s.s. was the most abundant species (95.95%) with An. rivulorum, An. parensis and An. rivulorum-like also detected. All An. gambiae s.l mosquitoes were identified as An. gambiae. High levels of pyrethroid resistance were observed in both An. gambiae and An. funestus mosquitoes. RT-qPCR analyses revealed a significant overexpression of two genes encoding D7 proteins, D7r3 and D7r4, in pyrethroids resistant An. funestus. However, no association was observed between the polymorphism of these genes and their overexpression. In contrast, overall D7 salivary genes were under-expressed in pyrethroid resistant An. gambiae. This study provides preliminary evidences that pyrethroid resistance could influence blood meal intake through over-expression of D7 proteins although future studies will help establishing potential impact on vectorial capacity.

Bionomics and insecticides resistance profiling of malaria vectors at a selected site for experimental hut trials in central Cameroon

Background

Malaria vectors are increasingly developing resistance to insecticides across Africa. The impact of such resistance on the continued effectiveness of insecticide-based interventions remains unclear due to poor characterization of vector populations. This study reports the characterization of malaria vectors at Mibellon, a selected site in Cameroon for experimental hut study, including species composition, Plasmodium infection rate, resistance profiles and mechanisms.

Methods

Indoor resting blood-fed Anopheles mosquitoes were collected from houses at Mibellon in 2017 and forced to lay eggs to generate F₁ adult mosquitoes. Insecticides susceptibility bioassays were performed on the F₁ adult mosquitoes following the WHO protocol to assess resistance profile to insecticides. The molecular basis of resistance and Plasmodium infection rate were investigated using TaqMan genotyping.

Results

Anopheles funestus sensu stricto (s.s.) was predominant in Mibellon (80%) followed by Anopheles gambiae s.s. (20%). High levels of resistance to pyrethroids and organochlorides were observed for both species. Moderate resistance was observed against bendiocarb (carbamate) in both species, but relatively higher in An. gambiae s.s. In contrast, full susceptibility was recorded for the organophosphate malathion. The PBO synergist assays with permethrin and deltamethrin revealed a significant recovery of the susceptibility in Anopheles funestus s.s. population (48.8 to 98.1% mortality and 38.3 to 96.5% mortality, respectively). The DDT/pyrethroid 119F-GSTe2 resistant allele (28.1%) and the dieldrin 296S-RDL resistant (9.7%) were detected in An. funestus s.s. The high pyrethroid/DDT resistance in An. gambiae correlated with the high frequency of 1014F knockdown resistance allele (63.9%). The 1014S-kdr allele was detected at low frequency (1.97%). The Plasmodium infection rate was 20% in An. gambiae, whereas An. funestus exhibited an oocyst rate of 15 and 5% for the sporozoite rate.

Conclusion

These results highlight the increasing spread of insecticide resistance and the challenges that control programmes face to maintain the continued effectiveness of insecticide-based interventions.

Elevated Plasmodium infection rates and high pyrethroid resistance in major malaria vectors in a forested area of Cameroon highlight challenges of malaria control

BACKGROUND

High coverage of long-lasting insecticidal nets (LLINs) is the cornerstone of the malaria control strategy of the national malaria control program (NMCP) in Cameroon, with a target of reducing malaria transmission to less than 10% by 2035. To this end, more than 20 million LLINs have been distributed to populations countrywide since 2011. The present study evaluated entomological indices and Anopheles susceptibility to pyrethroids in a rural forested area of south Cameroon with high coverage of LLINs.

METHODS

The study was conducted between July 2014 and May 2016 in Obout, a village located in a rural forested area in south Cameroon. Resting mosquitoes were collected using electric aspirators and were identified to species using morphological criteria and PCR tools. Mosquito feeding preferences and infection status to Plasmodium falciparum were determined by ELISA and using TaqMan assays. The susceptibility of wild F1 adults to pyrethroids was monitored using WHO insecticide susceptibility bioassays.

RESULTS

During the study period, 5,993 Anopheles mosquitoes were collected indoors both in rooms with and without nets. Two main vector species, namely An. funestus and An. gambiae, were identified in the locality, with An. funestus being by far the most abundant (89.68%). ELISA analysis revealed high percentage of blood meal taken exclusively on human (97.65-98.95%) supporting the high antropohilic behaviour of both species. Plasmodium falciparum infection rate detected by ELISA was high throughout the study period and varied between 3.28-14.04% (mean: 10.40%) in An. funestus, and between 5.55-22.22% (mean: 13.87%) in An. gambiae. This trend was confirmed by TaqMan assays, with P. falciparum infection prevalence of 23.33% in An. funestus. Significant decrease of mortality associated with high frequency of kdr mutation was observed in An. gambiae (deltamethrin: 36.6-56.45%; permethrin: 6-18.65%) indicating high level of resistance to pyrethroids. For An. funestus, resistance was marked for deltamethrin (mortality: 70.54-76.24%) than for permethrin (94.12-94.74%).

CONCLUSIONS

Our study showed that despite LLINs, the population of Obout remains exposed to bites of highly infected An. funestus and An. gambiae mosquitoes, highlighting the challenges to controlling malaria in forested areas, especially in the presence of insecticide resistance.