Effects of larval diet on the life-history traits and phenotypic expression of pyrethroid resistance in the major malaria vector Anopheles gambiae s.s.

The success achieved in reducing malaria transmission by vector control is threatened by insecticide resistance. To strengthen the current vector control programmes, the non-genetic factors underlying the emergence of insecticide resistance in Anopheles vectors and its widespread need to be explored. This study aimed to assess the effects of larval diet on some life-history traits and pyrethroid-insecticide susceptibility of Anopheles gambiae s.s. Three (3) An. gambiae strains, namely Kisumu (insecticide susceptible), AcerKis (homozygous ace-1 R G119S resistant) and KisKdr (homozygous kdr R L1014F resistant) were fed with three different diets (low, medium, and high) of TetraMin ® Baby fish food. Pre-imaginal developmental time, larval mortality, adult emergence rate and female wing length were measured. Mosquito females were exposed to insecticide-treated net (ITN) PermaNet 2.0 and PermaNet 3.0. In the three An. gambiae strains, significant differences in adult emergence rates ( F = 1054.2; df = 2; p <0.01), mosquito wing length ( F = 970.5; df = 2; p <0.01) and adult survival post insecticide exposure ( χ2 = 173; df = 2; p <0.01), were noticed among the three larval diets. Larvae fed with the low food diets took more time to develop, were smaller at emergence and displayed a short lifespan, while the specimens fed with a high regime developed faster and into big adults. Although being fed with a high diet, none of An. gambiae strain harbouring the kdr R and ace-1 R allele survived 24 hours after exposure against PermaNet 3.0. This study showed that variation in the larval diet significantly impacts An. gambiae life-history traits such as larval mortality and developmental time, adult wing length, and female susceptibility to pyrethroid insecticides. Further investigations through field-based studies would allow an in-depth understanding of the implications of these non-genetic parameters on the physiological traits of malaria vectors and consequently improve resistance management.

Adult Anopheles Mosquito Distribution at a Low and High Malaria Transmission Site in Tanzania

Malaria parasites are only transmitted by female mosquitoes of the genus Anopheles; hence, the disease’s distribution is linked to that of the vector mosquitoes. As such, the goal of this study was to find out the spatial and temporal distribution of Anopheles mosquito adults in the research sites. This was a repeated cross-sectional ecological study that took place in Morogoro and Dodoma, Tanzania. Vacuum aspiration was used to collect mosquitoes both outside and inside human dwellings. All mosquito-related data was collected and entered into appropriate data collection forms. Female mosquitoes were recognized morphologically using Gillies and Coetzee morphological criteria, followed by PCR. In total, about 2742 Anopheles mosquitoes with an average collection of 18.21 ± 1.12 per day were collected outside human houses of which 1717 ( 10.51 ± 1.17 ) and 1025 ( 8.42 ± 1.41 ) were collected from Morogoro and Dodoma, respectively. Of the captured mosquitoes, 89.0%, 10.0%, and 1.0% were recognized as Anopheles arabiensis, Anopheles gambiae s.s., and Anopheles quadrianulatus, respectively. The distribution varied significantly with seasons, whereby 302 ( 4.72 ± 1.04 ) and 2440 ( 12.96 ± 1.52 ) mosquitoes were captured in the cold-dry and warm-wet season, respectively ( p < 0.0001 ). Of the captured mosquitoes, 42.33%, 16.33%, 14.96%, and 4.27 were found on the ceiling, stored junks, verandas, and barks/tree, respectively. In malaria-endemic countries, vector control forms an important component of the malaria control efforts. This study found significant variation of Anopheles mosquito abundance in time and space with Anopheles arabiensis being the most predominant malaria vector. This signifies the need to introduce mosquito control methods that will target the less anthropophilic Anopheles arabiensis or the immature aquatic stages. The study further found that underbeds, store room/piled bags, and undisturbed curtains were the most preferred resting places by mosquitoes signifying to be the most effective strategic sites for spraying insecticides during the implementation of indoor residual spraying (IRS).

Microsporidia MB is found predominantly associated with Anopheles gambiae s.s and Anopheles coluzzii in Ghana

A vertically transmitted microsporidian, Microsporidia MB, with the ability to disrupt Plasmodium development was reported in Anopheles arabiensis from Kenya, East Africa. To demonstrate its range of incidence, archived DNA samples from 7575 Anopheles mosquitoes collected from Ghana were screened. MB prevalence was observed at 1.8%. An. gambiae s.s constituted 87% of positive mosquitoes while the remaining were from An. coluzzii. Both sibling species had similar positivity rates (24% and 19%; p = 0.42) despite the significantly higher number of An. gambiae s.s analysed (An. gambiae s.s = 487; An. coluzzii = 94; p = 0.0005). The microsporidian was also more prevalent in emerged adults from field-collected larvae than field-caught adults (p < 0.0001) suggestive of an efficient vertical transmission and/or horizontal transfer among larvae. This is the first report of Microsporidia MB in Anopheles mosquitoes in West Africa. It indicates possible widespread among malaria vector species and warrants investigations into the symbiont’s diversity across sub-Saharan Africa.

Malaria Transmission, Vector Diversity, and Insecticide Resistance at a Peri-Urban Site in the Forest Zone of Ghana

IntroductionRecent surge of Anopheles resistance to major classes of World Health Organization (WHO)-approved insecticides globally necessitates the need for information about local malaria vector populations. It is believed that insecticide efficacy loss may lead to operational failure of control interventions and an increase in malaria infection transmission. We investigated the susceptibility levels of malaria vectors to all classes of WHO-approved vector control insecticides and described the dynamics of malaria transmission in a peri-urban setting.MethodsFit 3–5-day-old adults that emerged from Anopheles larvae collected from several different sites in the study area were subjected to the WHO bioassay for detecting insecticide resistance. The knockdown resistance gene (kdr) mutations within the vector populations were detected using PCR. Entomological inoculation rates were determined using the human landing catch technique and Plasmodium falciparum circumsporozoite ELISA.ResultsThe malaria vectors from the study area were resistant to all classes of insecticides tested. Out of the 284 Anopheles complex specimen assayed for the resistance study, 265 (93.30%) were identified as Anopheles gambiae s.s. The kdr gene was detected in 90% of the Anopheles gambiae s.s. assayed. In an area where Anopheles coluzzii resistance to insecticides had never been reported, the kdr gene was detected in 78% of the Anopheles coluzzii sampled. The entomological inoculation rate (EIR) for the dry season was 1.44 ib/m/n, whereas the EIR for the rainy season was 2.69 ib/m/n.ConclusionsThis study provides information on the high parasite inoculation rate and insecticide resistance of malaria vectors in a peri-urban community, which is critical in the development of an insecticide resistance management program for the community.

Transcriptome Profiles of Anopheles gambiae Harboring Natural Low-Level Plasmodium Infection Reveal Adaptive Advantages for the Mosquito

Anopheline mosquitoes are the sole vectors for the Plasmodium pathogens responsible for malaria, which is among the oldest and most devastating of human diseases. The continuing global impact of malaria reflects the evolutionary success of a complex vector-pathogen relationship that accordingly has been the long-term focus of both debate and study. An open question in the biology of malaria transmission is the impact of naturally occurring low-level Plasmodium infections of the vector on mosquito health and longevity as well as critical behaviors such as host-preference/seeking. To begin to answer this, we have completed a comparative RNAseq-based transcriptome profile study examining the effect of biologically salient, salivary gland transmission-stage Plasmodium infection on the molecular physiology of Anopheles gambiae s.s. head, sensory appendage, and salivary glands. When compared with their uninfected counterparts, Plasmodium infected mosquitoes exhibit increased transcript abundance of genes associated with olfactory acuity as well as a range of synergistic processes that align with increased fitness based on both anti-aging and reproductive advantages. Taken together, these data argue against the long-held paradigm that malaria infection is pathogenic for anophelines and, instead, suggests there are biological and evolutionary advantages for the mosquito that drive the preservation of its high vectorial capacity.

Presence of L1014F Knockdown-Resistance Mutation in Anopheles gambiae s.s. From São Tomé and Príncipe

Malaria, one of the most serious parasitic diseases, kills thousands of people every year, especially in Africa. São Tomé and Príncipe are known to have stable transmission of malaria. Indoor residual spraying (IRS) of insecticides and long-lasting insecticidal nets (LLIN) are considered as an effective malaria control interventions in these places. The resistance status of Anopheles gambiae s.s. from Agua Grande, Caue, and Lemba of São Tomé and Príncipe to insecticides, such as dichlorodiphenyltrichloroethane (DDT) (4.0%), deltamethrin (0.05%), permethrin (0.75%), fenitrothion (1.0%), and malathion (5.0%), were tested according to the WHO standard protocol. DNA extraction, species identification, as well as kdr and ace-1R genotyping were done with the surviving and dead mosquitoes post testing. They showed resistance to cypermethrin with mortality rates ranging from 89.06% to 89.66%. Mosquitoes collected from Agua Grande, Caue, and Lemba displayed resistance to DDT and fenitrothion with mortality rates higher than 90%. No other species were detected in these study localities other than Anopheles gambiae s.s. The frequency of L1014F was high in the three investigated sites, which was detected for the first time in São Tomé and Príncipe. No ace-1R mutation was detected in all investigated sites. The high frequency of L1014F showed that kdr L1014F mutation might be related to insecticide resistance to Anopheles gambiae s.s. populations from São Tomé and Príncipe. Insecticide resistance status is alarming and, therefore, future malaria vector management should be seriously considered by the government of São Tomé and Príncipe.

Temporal Distribution and Abundance of Mosquito Vectors in Dhaka City

Species of Anopheles, Aedes and Culex mosquitoes showed that Anopheles gambiae s.s had the highest number (43.5%) out of the three malaria vectors (viz. Anopheles gambiae, An. arabiensis and An. funestus). For Aedes and Culex species, Aedes aegypti (37.6%) and Culex fatigans (37.1%) had the highest prevalence out of their sibling species. Temperature and rainfall were highly correlated with the abundance of mosquito vectors. It was observed that the rainy season (March to October) recorded the highest number (Total 11 specie) of mosquito vectors collected with the peak (Aedes aegypty, 140) in the months of July (932) and August (976) while the lowest (333) collection was in the dry season (November to February) with lowest (333) in the month of February when there was little or no rains. Asiat. Soc. Bangladesh, Sci. 46(1): 27-35, June 2020

Aeollanthus Pubescens Benth Leaf Essential Oil: Its Chemical Composition and the Insecticidal Activity Against the Malaria Vector Anopheles Gambiae (Diptera: Culicidae)

Background: The use of synthetic insecticides is responsible for many cases of resistance in insects. Therefore, the use of natural molecules of ecological interest with insecticidal properties turns out to be an alternative approach to the use of synthetic insecticides. This study aims at investigating the larvicidal, adulticidal activity and the chemical composition of the essential oil of Aeollanthus pubescens Benth on the major malaria vector Anopheles gambiae.The leaves of Aeollanthus pubescens were collected in the South of the Republic of Benin.Methods: Three reference strains of Anopheles gambiae s.s. such as Kisumu, Kiskdr and Acerkis were used. The standard WHO guideline for larvicides evaluation was used and the chemical composition of the essential oil was analysed by gas chromatography coupled to mass spectrometry. Adult mosquitoes were exposed to the fragment nets coated with the essential oil for 3 min. Probit regression analysis was used for LC50 , LC95 , KDT50 , and KDT95 calculations. The difference between the mortality‐dose regressions for the different strains was analysed using the likelihood ratio test (LRT). The Log-rank test was performed to evaluate the difference in survival between the strains.Results: Fourteen components were identified representing 98.31% of the total of oil. The major components were carvacrol (51.06 %), thymyle acetate (14.01 %) and ɣ-terpinene (10.60 %). The essential oil has remarkable larvicidal properties with LC50 of 29.57, 22.95, and 28.37 ppm respectively on Kisumu, Acerkis and Kiskdr strains. With the fragment net treated at 165 µg/cm2, the KDT50 of both Acerkis (1.71 s, p < 0.001) and Kiskdr (2.67 s, p < 0.001) individuals were significantly lower than that of Kisumu (3.77 s). The lifespan of the three mosquito strains decreased respectively to one day for Kisumu (p < 0.001), two days for Acerkis (p < 0.001) and three days for Kiskdr (p < 0.001) compared to their control.Conclusion: Our findings show that the Aeollanthus pubescens essential oil is an efficient larvicide and adulticide against malaria vector Anopheles gambiae. This bioinsecticidal activity is a promising discovery for the control of the resistant malaria-transmitting vectors.

Larvicidal potency of Dioscorea sansibarensis leaf extract against vector mosquitoes: Anopheles gambiae s.s. and Culex quinquefasciatus

Mosquitoes are responsible for transmission of illnesses of public health importance including malaria, lymphatic filariasis, dengue, chikungunya, and many other diseases caused by viruses. Vector control using synthetic insecticides has been the cornerstone for management of vector-borne diseases. However, the chemical based interventions have not been sustainable due to emergency of resistance against insecticides among disease vectors. Plant based mosquitocidal products can be potential alternative tools in vector control. Therefore, the present study aimed at exploring the larvicidal properties of Dioscorea sansibarensis leaf extract against malaria and lymphatic filariasis vectors; Anopheles gambiae s.s. and Culex quinquefasciatus. The larvicidal activities of Dioscorea sansibarensis were assessed following WHO test procedures. Ethanol leaf extract of Dioscorea sansibarensis was evaluated against all the four instar larvae stages of An. gambiae s.s and Cx. quinquefasciatus susceptible laboratory colonies. The highest larvicidal potency was shown against the 4th instar stages of both species with the LC50 values of 60.915 ppm and 80.700 ppm for Cx. quinquefasciatus and An. gambiae s.s., respectively. The respective LC95 values for Cx. quinquefasciatus and An. gambiae s.s. were 168.898 ppm and 249.295 ppm. This implies that the extract can be applied as mosquito larvicide should its impact on non-targeted species be established. Keywords: Dioscorea sansibarensis; vectors, mosquitoes, Zanzibar yams, Dar es Salaam, Tanzania

Influence of geographical location on abundance assortment of Anopheles mosquito species (Diptera: Culicidae) on malaria parasite rate in Enugu State, Nigeria

Assessment of geographical distribution of malaria vectors is essential to effective malaria parasite control. This study evaluated the influence of geographical locations on distribution of Anopheles mosquito species and malaria parasite vectorial efficacy in Enugu State, Nigeria. Mosquitoes were collected, using indoor resting pyrethrum spray collection (IRPSC) method. They were morphologically identified and molecularly (PCR) characterised. The M form (now called Anopheles coluzzii) and S form (now called nominotypical Anopheles gambiae s.s.), were identified using Restriction Fragment Length Polymorphism (RFLP). Plasmodium falciparum sporozoite rates of sampled mosquitoes and malaria status of households were evaluated microscopically and by using rapid diagnostic kits. An. gambiae Giles (sensu stricto), and bands resembling An. melas and An. arabiensisspecies complexes were observed. Out of 300 An. gambiae s.l. identified using PCR, 243 were An. gambiae Giles (sensu stricto), 6 were An. melas and 5 were An. arabiensis. Out of the 243 An. gambiae Giles (sensu stricto), 184 were M form (now An. coluzzii) and 59 were S form (now nominotypical An. gambiae s.s).The M form (now An. coluzzii) constituted 99% of Anopheles mosquitoes from southernmost part of the study area while northernmost part showed 100% S form (An. gambiae s.s.). The median location had the M form (An. coluzzii) and S form (An. gambiae s.s.) in sympatric. Sporozoite rate in northernmost area was highest when compared with median and southernmost parts. The S form (An. gambiae s.s.) was observed as more important malaria parasite vector, and the results revealed that geographical location affected species diversities which is an important consideration for malaria control programme. Keywords: Anopheles, distribution, sporozoite, malaria parasite