Resistance status of Anopheles gambiae (s.l.) to four commonly used insecticides for malaria vector control in South-East Nigeria

Treatment outcomes and associated factors in severe malaria patients at University of Gondar Hospital, Northwest Ethiopia: A retrospective study (2020-2023)

BACKGROUND

Malaria continues to be the most prevalent life-threatening parasitic illness in Ethiopia. Its clinical spectrum ranges from mild to severe, with a propensity for death. In Ethiopia, it accounts for 10% of hospital admission. Identifying predictors of malaria-related mortality is crucial for aiding high-risk patient identification and enabling timely intervention.

OBJECTIVE

Our study aimed to assess treatment outcomes and factors associated with mortality among severe malaria patients at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia.

METHODS

A retrospective cross-sectional study examined 383 randomly chosen patients with severe malaria, spanning a four-year period leading up to the data collection date, encompassing July 2023 back to June 2020. Data were collected from the hospital records. A structured questionnaire was used to collect the data. EpiData version 3.1 and SPSS version 20 were used to clean and analyze the data, respectively. Logistic regression analysis was conducted to determine associations and reported by the odds ratio at p < 0.05 with 95% confidence intervals.

RESULTS

Among the 383 eligible patients, the majorities were males (56.66%) and resided in rural areas (66.32%). Over 84% of them were referred from health facilities. Plasmodium falciparum was the major parasite identified in 78% of cases. The magnitude of death among severe malaria patients was 10.97%. Impaired consciousness, convulsions, jaundice, parasitemia level >2, and creatinine level ≥3 were significantly associated with death, with adjusted odds ratios (AOR) of 3.4 (95% CI: 1.3-8.3), 2.7 (95% CI: 1.004-7.492), 3.2 (95% CI: 1.173-9.182), 3.7 (95% CI: 1.516-9.113), and 11.7 (95% CI: 4.756-29.239), respectively.

CONCLUSION

Our study revealed a significant number of malaria-related deaths, with predictors such as age, impaired consciousness, convulsions, jaundice, parasitemia level, and creatinine level identified. Hence, it is imperative to implement intense and timely interventions for patients exhibiting these clinical manifestations to prevent malaria-related fatalities.

Organophosphate and carbamate susceptibility profiling of Anopheles gambiae sl. across different ecosystems in southern Benin

Background

To overcome the spread of high pyrethroid resistance in the main malaria vectors and malaria disease persistence, it is crucial to look for effective and better resistance management strategies. Understanding the phenotypic profile of Anopheles gambiae sl. against alternatives insecticides like organophosphates and carbamates is crucial.

Methods

Anopheles larvae and pupae were collected from the breeding sites in rice fields, pineapple crop areas, and peri-urban areas. WHO susceptibility tests were conducted on unfed female mosquitoes aged 3-5 days old. Mosquitoes were exposed to malathion 5%, pirimiphos-methyl 0.25%, and bendiocarb 0.1% using the standard WHO protocol. Polymerase chain reaction (PCR) techniques were used to detect species, kdr and Ace-1 mutations.

Results

Anopheles gambiae sl. from Sèdjè-Dénou rice field population was resistant to bendiocarb (0.1%) with a mortality rate of 72.2% whereas Anopheles gambiae sl. populations from Zinvié-Dokomey (rice field), Zè-Tozounmè (pineapple field), and Adjagbo (peri-urban area) were suspected to be resistant with mortality rates of 90%, 93.5%, 95.4% respectively. However, all of them were susceptible to organophosphates (malathion and pirimiphos-methyl) with a mortality rate of 100%. PCR assay revealed that 100% of the mosquitoes tested were Anopheles coluzzii. The frequencies of Ace-1R mutation in all Anopheles coluzzii populations tested were low (3-27%).

Conclusions

Organophosphates (malathion and pirimiphos-methyl) have maintained their efficacy against Anopheles coluzzii populations from Sèdjè-Dénou (rice field), Zè Tozounmè (pineapple field), Zinvié Dokomey (rice field), or Adjagbo (peri-urban area). The good efficacy of these organophosphates against Anopheles coluzzii populations from the southern part of Benin are observed in the current study. The use of pirimiphos-methyl for IRS in this part of the country would be a successful alternative for malaria control in this area.

An observational analysis of the impact of deltamethrin + piperonyl butoxide insecticide-treated nets on malaria case incidence and entomological indicators in Ebonyi State, Nigeria, 2017-2021

BACKGROUND

Intense pyrethroid resistance threatens the effectiveness of the primary vector control intervention, insecticide-treated nets (ITNs), in Nigeria, the country with the largest malaria burden globally. In this study, the epidemiological and entomological impact of a new type of ITN (piperonyl-butoxide [PBO] ITNs) distributed in Ebonyi State were evaluated. The epidemiological impact was also compared to the impact of standard pyrethroid-only ITNs in Cross River State.

METHODS

A controlled interrupted time series analysis was conducted on monthly malaria incidence data collected at the health facility level, using a multilevel mixed-effects negative binomial model. Data were analysed two years before and after the PBO ITN campaign in Ebonyi State (December 2017 to November 2021). A pre-post analysis, with no comparison group, was used to assess the impact of PBO ITNs on human biting rates and indoor resting density in Ebonyi during the high transmission season immediately before and after the PBO ITN campaign.

RESULTS

In Ebonyi, PBO ITNs were associated with a 46.7% decrease (95%CI: -51.5, -40.8%; p < 0.001) in malaria case incidence in the 2 years after the PBO ITN distribution compared to a modelled scenario of no ITNs distributed, with a significant decrease from 269.6 predicted cases per 1000 population to 143.6. In Cross River, there was a significant 28.6% increase (95%CI: -10.4, 49.1%; p < 0.001) in malaria case incidence following the standard ITN distribution, with an increase from 71.2 predicted cases per 1000 population to 91.6. In Ebonyi, the human biting rate was 72% lower (IRR: 0.28; 95%CI 0.21, 0.39; p < 0.001) and indoor resting density was 73% lower (IRR: 0.27; 95%CI 0.21, 0.35; p < 0.001) after the PBO ITNs were distributed.

CONCLUSIONS

The epidemiological and entomological impact of the PBO ITNs underscore the impact of these ITNs in areas with confirmed pyrethroid resistance. These findings contribute to ongoing research on the impact of new types of ITNs in Nigeria, providing critical evidence for the Nigeria National Malaria Elimination Programme and other countries for future ITN procurement decisions as part of mass ITN campaign planning and malaria programming.

Sibling species of the major malaria vector Anopheles gambiae display divergent preferences for aquatic breeding sites in southern Nigeria

BACKGROUND

When integrated with insecticide-treated bed nets, larval control of Anopheles mosquitoes could fast-track reductions in the incidence of human malaria. However, larval control interventions may deliver suboptimal outcomes where the preferred breeding places of mosquito vectors are not well known. This study investigated the breeding habitat choices of Anopheles mosquitoes in southern Nigeria. The objective was to identify priority sites for mosquito larval management in selected urban and periurban locations where malaria remains a public health burden.  METHODS: Mosquito larvae were collected in urban and periurban water bodies during the wet-dry season interface in Edo, Delta, and Anambra States. Field-collected larvae were identified based on PCR gel-electrophoresis and amplicon sequencing, while the associations between Anopheles larvae and the properties and locations of water bodies were assessed using a range of statistical methods.

RESULTS

Mosquito breeding sites were either man-made (72.09%) or natural (27.91%) and mostly drainages (48.84%) and puddles (25.58%). Anopheles larvae occurred in drainages, puddles, stream margins, and a concrete well, and were absent in drums, buckets, car tires, and a water-holding iron pan, all of which contained culicine larvae. Wild-caught Anopheles larvae comprised Anopheles coluzzii (80.51%), Anopheles gambiae sensu stricto (s.s.) (11.54%), and Anopheles arabiensis (7.95%); a species-specific PCR confirmed the absence of the invasive urban malaria vector Anopheles stephensi among field-collected larvae. Anopheles arabiensis, An. coluzzii, and An. gambiae s.s. displayed preferences for turbid, lowland, and partially sunlit water bodies, respectively. Furthermore, An. arabiensis preferred breeding sites located outside 500 m of households, whereas An. gambiae s.s. and An. coluzzii had increased detection odds in sites within 500 m of households. Anopheles gambiae s.s. and An. coluzzii were also more likely to be present in natural water bodies; meanwhile, 96.77% of An. arabiensis were in man-made water bodies. Intraspecific genetic variations were little in the dominant vector An. coluzzii, while breeding habitat choices of populations made no statistically significant contributions to these variations.

CONCLUSION

Sibling malaria vectors in the An. gambiae complex display divergent preferences for aquatic breeding habitats in southern Nigeria. The findings are relevant for planning targeted larval control of An. coluzzii whose increasing evolutionary adaptations to urban ecologies are driving the proliferation of the mosquito, and An. arabiensis whose adults typically evade the effects of treated bed nets due to exophilic tendencies.

Single and Combined Mutations of Acetylcholinesterase Gene Giving Resistance to Pirimiphos-Methyl in Musca domestica Slaughterhouse Populations

The house fly Musca domestica L. (Diptera: Muscidae) is a worldwide medical and veterinary pest, causing great economic losses. Organophosphate insecticides have been widely used to control house fly populations. The main objectives of the present study were to evaluate the resistance levels of M. domestica slaughterhouse populations, collected from Riyadh, Jeddah, and Taif, against the organophosphate insecticide pirimiphos-methyl and investigate the genetic mutations of the Ace gene associated with pirimiphos-methyl resistance. The obtained data showed that there were significant differences among pirimiphos-methyl LC₅₀ values of the studied populations, where the highest LC₅₀ was recorded for the Riyadh population (8.44 mM), followed by Jeddah and Taif populations (2.45 mM and 1.63 mM, respectively). Seven nonsynonymous SNPs were detected in the studied house flies. The Ile239Val and Glu243Lys mutations are reported for the first time, whereas Val260Leu, Ala316Ser, Gly342Ala, Gly342Val, and Phe407Tyr were previously reported in M. domestica field populations from other countries. Considering three mutations associated with insecticide resistance, at amino acid positions 260, 342, and 407 of acetylcholinesterase polypeptide, 17 combinations were recovered in this study. Three out of these seventeen combinations were frequently found both worldwide and in the three Saudi house fly field populations, as well as their pirimiphos-methyl-surviving flies. Overall, the single and combined Ace mutations are apparently associated with pirimiphos-methyl resistance, and the obtained data can be useful in managing house fly field populations in Saudi Arabia.

First comprehensive report of the resistance of Culex quinquefasciatus Say (Diptera: Culicidae) to commonly used insecticides in Riyadh, Saudi Arabia

The mosquito Culex quinquefasciatus is a vector of various pathogens including West Nile virus, Saint Louis encephalitis virus, and Western equine encephalitis virus. Insecticides are the main tools for Cx. quinquefasciatus control, but this overreliance on chemical tools has led to the development of resistance to many insecticides in this important insect vector. The resistance of eight field populations of Cx. quinquefasciatus to 10 commonly used insecticides was evaluated. Based on the resistance ratios (RRs), the adults of Cx. quinquefasciatus field populations displayed susceptibility to the organophosphates (OPs) except Al-Masanie adults which exhibited low resistance to fenitrothion (RR₅₀ = 3.62). Conversely, the mosquitoes exhibited susceptibility, low resistance, and moderate resistance to the pyrethroids alpha-cypermethrin (RR = 0.59-2.56), bifenthrin (RR = 0.59-2.19), deltamethrin (RR = 0.60-7.07), cypermethrin (RR = 0.60-2.66), and cyfluthrin (RR = 0.58-2.39). At the larval stage, Cx. quinquefasciatus field populations displayed susceptibility to low resistance to the OPs chlorpyrifos (RR = 0.03-1.75), malathion (RR = 0.19-3.42), fenitrothion (RR = 0.11-2.78), and pirimiphos-methyl (RR = 0.08-1.15). Although these results in Cx. quinquefasciatus field populations indicated that the OPs and pyrethroids maintained high efficacy in controlling this species in the geographical area of this study, these findings should be utilized wisely to avoid any potential negative effects on human health and environmental safety attributable to the application of these broad-spectrum conventional insecticides. However, these findings provide a solid basis for decision-making for Cx. quinquefasciatus integrated vector management programs.

Insecticidal effectiveness of naphthalene and its combination with kerosene against the emergence of Aedes aegypti in Ika North East, LGA, Delta State, Nigeria

Despite the substantial progress achieved in the search of nonchemical alternatives to insecticidal larviciding on mosquitoes, more work is still required to unravel the potency of viable substances in order to attend to several pest and disease problems. Insecticidal effectiveness of naphthalene and its combination with kerosene against the emergence of Ae. aegypti in Ika North East, LGA, Delta State, Nigeria was assessed. Immature stages of Ae. aegypti were collected and left to acclimatize for 6 h in standard laboratory conditions. Naphthalene measured in 2 g and its combinations with kerosene in 50:50 were emptied in 400 ml, 200 ml and 100 ml of water which resulted in 0.005%, 0.01% and 0.02% concentrations respectively. Water alone served as control for the experiment. Twenty third instar larvae and pupae were sorted into containers before exposure to treatments. Experiment was done in triplicates and observed for 10, 15, 20, 30, 40, 50, 60, and 80 min coinciding with WHO protocol for Aedes exposure. Mortality was highest in larvae exposed to 0.02% kerosene and naphthalene, and was also high in 0.02% naphthalene. Lowest mortality was recorded in pupae exposed to 0.005% of naphthalene. Significant differences in toxicity was recorded (p < 0.05). Mortality increased with time in larvae and pupae. Highest mortality in pupae and larvae was recorded in 0.02% kerosene and naphthalene mixture at 80 min post exposure time respectively. LC₅₀ and LC₉₅ of naphthalene exposed to Aedes larvae and pupae was between 0.002 and 0.018% and 0.021–0.051% respectively. Similarly, for naphthalene with kerosene was between 0.002 and 0.007%, and 0.015–0.035%. Pupae exposed to 0.005% naphthalene had more adult emergence than in others and the differences were significant (p < 0.05). Field trial is required with optimum concentrations.

Spatial variation and risk factors of malaria and anaemia among children aged 0 to 59 months: a cross-sectional study of 2010 and 2015 datasets

Malaria and anaemia are common diseases that affect children, particularly in Africa. Studies on the risk associated with these diseases and their synergy are scanty. This work aims to study the spatial pattern of malaria and anaemia in Nigeria and adjust for their risk factors using separate models for malaria and anaemia. This study used Bayesian spatial models within the Integrated Nested Laplace Approach (INLA) to establish the relationship between malaria and anaemia. We also adjust for risk factors of malaria and anaemia and map the estimated relative risks of these diseases to identify regions with a relatively high risk of the diseases under consideration. We used data obtained from the Nigeria malaria indicator survey (NMIS) of 2010 and 2015. The spatial variability distribution of both diseases was investigated using the convolution model, Conditional Auto-Regressive (CAR) model, generalized linear mixed model (GLMM) and generalized linear model (GLM) for each year. The convolution and generalized linear mixed models (GLMM) showed the least Deviance Information Criteria (DIC) in 2010 for malaria and anaemia, respectively. The Conditional Auto-Regressive (CAR) and convolution models had the least DIC in 2015 for malaria and anaemia, respectively. This study revealed that children in rural areas had strong and significant odds of malaria and anaemia infection [2010; malaria: AOR = 1.348, 95% CI = (1.117, 1.627), anaemia: AOR = 1.455, 95% CI = (1.201, 1.7623). 2015; malaria: AOR = 1.889, 95% CI = (1.568, 2.277), anaemia: AOR = 1.440, 95% CI = (1.205, 1.719)]. Controlling the prevalence of malaria and anaemia in Nigeria requires the identification of a child’s location and proper confrontation of some socio-economic factors which may lead to the reduction of childhood malaria and anaemia infection.

Assessing Anopheles vector species diversity and transmission of malaria in four health districts along the borders of Côte d'Ivoire

BACKGROUND

Although malaria and Anopheles mosquito vectors are highly prevalent in Côte d'Ivoire, limited data are available to help understand the malaria vector density and transmission dynamics in areas bordering the country. To address this gap, the Anopheles mosquito species diversity, the members of the Anopheles gambiae complex and the transmission of malaria were assessed in four health districts along the borders of Côte d'Ivoire.

METHODS

From July 2016 through December 2016 and July 2017 through December 2017, adult Anopheles mosquitoes were collected in four health districts of Côte d'Ivoire (Aboisso, Bloléquin, Odienné and Ouangolodougou) using standardized window exit trap (WET) and pyrethrum knockdown spray collection (PSC) methods. The collected mosquitoes were identified morphologically at species level and the members of the An. gambiae complex were separated using short interspersed nuclear element-based polymerase chain reaction (SINE-PCR). Anopheles gambiae sensu lato (s.l.), Anopheles funestus s.l. and Anopheles nili specimens were analysed for malaria Plasmodium parasite detection using the cytochrome oxidase I gene (COX-I), and malaria prevalence among human population through local Ministry of Health (MoH) statistical yearbooks.

RESULTS

A total of 281 female Anopheles were collected in Aboisso, 754 in Bloléquin, 1319 in Odienné and 2443 in Ouangolodougou. Seven Anopheles species were recorded including An. gambiae s.l. (94.8-99.1%) as the main vector, followed by An. funestus s.l. (0.4-4.3%) and An. nili (0-0.7%). Among An. gambiae s.l., Anopheles coluzzii represented the predominant species in Aboisso (89.2%) and Bloléquin (92.2%), while An. gambiae sensu stricto (s.s.) was the major species in Odienné (96.0%) and Ouangolodougou (94.2%). The Plasmodium sporozoite infection rate in An. gambiae s.l. was highest in Odienné (11.0%; n = 100) followed by Bloléquin (7.8%, n = 115), Aboisso (3.1%; n = 65) and Ouangologoudou (2.5%; n = 120). In An. funestus s.l., Plasmodium falciparum sporozoite infection rate was estimated at 6.2% (n = 32) in Bloléquin, 8.7% (n = 23) in Odienné. No An. funestus s.l. specimens were found infected with P. falciparum sporozoite infection in Ouangolodougou and Aboisso. No P. falciparum sporozoite was detected in An. nili specimens in the four health districts. Among the local human populations, malaria incidence was higher in Odienné (39.7%; n = 45,376) and Bloléquin (37.6%; n = 150,205) compared to that in Ouangolodougou (18.3%; n = 131,629) and Aboisso (19.7%; n = 364,585).

CONCLUSION

Anopheles vector species diversity, abundance and Plasmodium sporozoite infection were high within the health districts along the borders of the country of Côte d'Ivoire, resulting in high malaria transmission among the local populations. Anopheles gambiae s.l. and An. funestus s.l. were found to be highly infected with Plasmodium in the health districts of Bloléquin and Odienné where higher malaria incidence was observed than the other districts. This study provides important information that can be used to guide Côte d'Ivoire National Malaria Control Programme for vector control decision-making, mainly in districts that are at the country borders.

Characterization of resistance profile (intensity and mechanisms) of Anopheles gambiae in three communes of northern Benin, West Africa

Background

The selection and the spread of insecticide resistance in malaria vectors to the main classes of insecticides used in vector control tools are a major and ongoing challenge to malaria vector control programmes. This study aimed to determine the intensity of vector resistance to insecticides in three regions of Benin with different agro-ecological characteristics.

Methods

Larvae of Anopheles gambiae sensu lato (s.l.) were collected from September to November 2017 in different larval sites in three northern Benin communes: Parakou, Kandi and Malanville. Two to five-day-old, non-blood-fed, female mosquitoes were exposed to papers impregnated with deltamethrin, permethrin and bendiocarb at dosages of 1 × the diagnostic dose, 5 × and 10 × to determine the intensity of resistance in these vectors. Molecular frequencies of the kdr L1014F and ace-1R G119S insecticide resistance mutations and levels of detoxification enzymes were determined for mosquitoes sampled at each study site.

Results

Resistance to pyrethroids (permethrin and deltamethrin) was recorded in all three communes with mortality rates below 60% using the diagnostic dose (1x). The results obtained after exposure of An. gambiae to permethrin 10 × were 99% in Kandi, 98% in Malanville and 99% in Parakou. With deltamethrin 10x, mortality rates were 100% in Kandi, 96% in Malanville and 73% in Parakou. For the diagnostic dose of bendiocarb, suspected resistance was recorded in the communes of Malanville (97%) and Kandi (94%) while sensitivity was observed in Parakou (98%).Using the 10 × dose, mortality was 98% in Kandi, 100% in Malanville and 99% in Parakou. The frequencies of the kdr L1014F allele varied between 59 and 83% depending on the sites and species of the An. gambiae complex, while the frequency of the ace-1R G119S gene varied between 0 and 5%. Biochemical tests showed high levels of oxidase and esterase activity compared to the susceptible colony strain of An. gambiae sensu stricto (Kisumu strain).

Conclusion

Anopheles gambiae showed a generalized loss of susceptibility to permethrin and deltamethrin but also showed moderate to high intensity of resistance in different regions of Benin. This high intensity of resistance is a potential threat to the effectiveness of vector control.

High pyrethroid/DDT resistance in major malaria vector Anopheles coluzzii from Niger-Delta of Nigeria is probably driven by metabolic resistance mechanisms

Entomological surveillance of local malaria vector populations is an important component of vector control and resistance management. In this study, the resistance profile and its possible mechanisms was characterised in a field population of the major malaria vector Anopheles coluzzii from Port Harcourt, the capital of Rivers state, in the Niger-Delta Region of Nigeria. Larvae collected in Port-Harcourt, were reared to adulthood and used for WHO bioassays. The population exhibited high resistance to permethrin, deltamethrin and DDT with mortalities of 6.7% ± 2.4, 37.5% ± 3.2 and 6.3% ± 4.1, respectively, but were fully susceptible to bendiocarb and malathion. Synergist bioassays with piperonylbutoxide (PBO) partially recovered susceptibility, with mortalities increasing to 53% ± 4, indicating probable role of CYP450s in permethrin resistance (χ2 = 29.48, P < 0.0001). Transcriptional profiling revealed five major resistance-associated genes overexpressed in the field samples compared to the fully susceptible laboratory colony, Ngoussou. Highest fold change (FC) was observed with GSTe2 (FC = 3.3 in permethrin exposed and 6.2 in unexposed) and CYP6Z3 (FC = 1.4 in exposed and 4.6 in unexposed). TaqMan genotyping of 32 F0 females detected the 1014F and 1575Y knockdown resistance (kdr) mutations with frequencies of 0.84 and 0.1, respectively, while 1014S mutation was not detected. Sequencing of a fragment of the voltage-gated sodium channel, spanning exon 20 from 13 deltamethrin-resistant and 9 susceptible females revealed only 2 distinct haplotypes with a low haplotype diversity of 0.33. The findings of high pyrethroid resistance but with a significant degree of recovery after PBO synergist assay suggests the need to move to PBO-based nets. This could be complemented with carbamate- or organophosphate-based indoor residual spraying in this area.

Resistance to pirimiphos-methyl in West African Anopheles is spreading via duplication and introgression of the Ace1 locus

Vector population control using insecticides is a key element of current strategies to prevent malaria transmission in Africa. The introduction of effective insecticides, such as the organophosphate pirimiphos-methyl, is essential to overcome the recurrent emergence of resistance driven by the highly diverse Anopheles genomes. Here, we use a population genomic approach to investigate the basis of pirimiphos-methyl resistance in the major malaria vectors Anopheles gambiae and A. coluzzii. A combination of copy number variation and a single non-synonymous substitution in the acetylcholinesterase gene, Ace1, provides the key resistance diagnostic in an A. coluzzii population from Côte d'Ivoire that we used for sequence-based association mapping, with replication in other West African populations. The Ace1 substitution and duplications occur on a unique resistance haplotype that evolved in A. gambiae and introgressed into A. coluzzii, and is now common in West Africa primarily due to selection imposed by other organophosphate or carbamate insecticides. Our findings highlight the predictive value of this complex resistance haplotype for phenotypic resistance and clarify its evolutionary history, providing tools to for molecular surveillance of the current and future effectiveness of pirimiphos-methyl based interventions.