Gambiae Mosquitoes Research Articles

How do mosquitoes smell us? The answers could help eradicate disease

In the coastal Rabai region of southeast Kenya, two populations of mosquitoes live within a half mile of each other but lead separate and curiously different lifestyles. Entomologists in the mid-20th century found that color distinguished the two subspecies of Aedes aegypti ( Aedes aegypti aegypti are brown and Aedes aegypti formosa are black) as well as the hosts they chose for blood meals. The “domestic” brown form frequented people’s homes, preferentially feeding on people and laying their eggs in indoor water receptacles. Meanwhile, the black-colored “forest” form roamed the nearby woods preferring to bite nonhuman animals and lay its eggs in tree trunk holes. This light sheet microscope image of an adult female Anopheles gambiae mosquito includes genetic labeling to show olfactory neurons (green). The antennae, maxillary palp, and labella on the proboscis contain many such neurons. Image courtesy of Olena Riabinina, Courtney Akitake, and Chris Potter (Johns Hopkins University School of Medicine, Baltimore). Following up on these reports some 50 years later as a postdoctoral fellow at The Rockefeller University in New York, Lindy McBride saw an opportunity to examine this natural case study with modern genetic tools. The feeding habits of Aedes aegypti aegypti make it a dangerously efficient vector for spreading yellow fever, dengue, Zika, and other diseases between humans. The other subspecies poses much less of a threat. To understand why, McBride traveled to Rabai to collect mosquito larvae and pupae from people’s homes and the nearby woods. She wanted to compare the two mosquitoes genetically and discover what changes had led the more recently evolved domestic form to hunt humans. Back at Rockefeller in the laboratory of her then-postdoctorate advisor Leslie Vosshall, McBride raised 30 strains of mosquitoes from the samples and used RNA sequencing to compare the genes expressed in their antennae (a major …

First report of the East African kdr mutation in an Anopheles gambiae mosquito in Côte d’Ivoire

Background. The intensive use of insecticides in public health and agriculture has led to the development of insecticide resistances in malaria vectors across sub-Saharan Africa countries in the last two decades. The kdr target site point mutation which is among the best characterised resistance mechanisms seems to be changing its distribution patterns on the African continent. The 1014F kdr mutation originally described only in West Africa is spreading to East Africa while the 1014S kdr mutation originally described in East Africa, is spreading to West and Central Africa. However, the East- kdr mutation has not been reported in Côte d'Ivoire so far. Methods. Immature stages of Anopheles gambiae s.l. were collected from breeding sites at the outskirts of Yamoussoukro, Côte d'Ivoire. Emerging 3–5 day old adult female mosquitoes were tested for susceptibility to deltamethrin 0.05%, malathion 5%, bendiocarb 1% and dichlorodiphenyltrichloroethane (DDT) 4% according to WHO standard procedures. A total of 50 An. gambiae s.l. specimens were drawn at random for DNA extraction and identification down to the species level. A subsample of 30 mosquitoes was tested for the East-African kdr mutation using a Taqman assay. Results. The tested mosquito population appeared to be strongly resistant to deltamethrin (1.03% mortality), bendiocarb (38.46% mortality) and DDT (0% mortality) with probable resistance observed for malathion (92.47%). Among the 41 mosquitoes that were successfully characterized, An. coluzzii was predominant (68.3%) followed by An. gambiae s.s. (19.5%) and a few hybrids (7.3%). Out of 30 specimens genotyped for East- kdr, a single hybrid mosquito appeared to be heterozygous for the mutation. Conclusion. The present study revealed the presence of the East- kdr mutation in Côte d’Ivoire for the first time in An. gambiae and highlights the urgent need to start monitoring the allele and genotype frequencies.

First report of the East African kdr mutation in an Anopheles gambiae mosquito in Côte d'Ivoire.

Background. The intensive use of insecticides in public health and agriculture has led to the development of insecticide resistances in malaria vectors across sub-Saharan Africa countries in the last two decades. The kdr target site point mutation which is among the best characterised resistance mechanisms seems to be changing its distribution patterns on the African continent. The 1014F kdr mutation originally described only in West Africa is spreading to East Africa while the 1014S kdr mutation originally described in East Africa, is spreading to West and Central Africa. However, the East-kdr mutation has not been reported in Côte d'Ivoire so far. Methods. Immature stages of Anopheles gambiae s.l. were collected from breeding sites at the outskirts of Yamoussoukro, Côte d'Ivoire. Emerging 3-5 day old adult female mosquitoes were tested for susceptibility to deltamethrin 0.05%, malathion 5%, bendiocarb 1% and dichlorodiphenyltrichloroethane (DDT) 4% according to WHO standard procedures. A total of 50 An.gambiaes.l. specimens were drawn at random for DNA extraction and identification down to the species level. A subsample of 30 mosquitoes was tested for the East-African kdr mutation using a Taqman assay. Results. The tested mosquito population appeared to be strongly resistant to deltamethrin (1.03% mortality), bendiocarb (38.46% mortality) and DDT (0% mortality) with probable resistance observed for malathion (92.47%). Among the 41 mosquitoes that were successfully characterized, An.coluzzii was predominant (68.3%) followed by An.gambiae s.s. (19.5%) and a few hybrids (7.3%). Out of 30 specimens genotyped for East-kdr, a single hybrid mosquito appeared to be heterozygous for the mutation. Conclusion. The present study revealed the presence of the East-kdr mutation in Côte d'Ivoire for the first time in An.gambiae and highlights the urgent need to start monitoring the allele and genotype frequencies.

Male mosquitoes sing from the same song sheet

Some close relatives can be hard to distinguish. Take the extensive Anopheles family of mosquitoes: until recently, Anopheles coluzzii and A. gambiae mosquitoes were thought to be members of the same species because they are almost perfectly identical. Yet, despite sharing much of the same

The Plasmodium falciparum Cell-Traversal Protein for Ookinetes and Sporozoites as a Candidate for Preerythrocytic and Transmission-Blocking Vaccines.

ABSTRACTRecent studies have shown that immune responses against the cell-traversal protein for Plasmodium ookinetes and sporozoites (CelTOS) can inhibit parasite infection. While these studies provide important evidence toward the development of vaccines targeting this protein, it remains unknown whether these responses could engage the Plasmodium falciparum CelTOS in vivo. Using a newly developed rodent malaria chimeric parasite expressing the P. falciparum CelTOS (PfCelTOS), we evaluated the protective effect of in vivo immune responses elicited by vaccination and assessed the neutralizing capacity of monoclonal antibodies specific against PfCelTOS. Mice immunized with recombinant P. falciparum CelTOS in combination with the glucopyranosyl lipid adjuvant-stable emulsion (GLA-SE) or glucopyranosyl lipid adjuvant-liposome-QS21 (GLA-LSQ) adjuvant system significantly inhibited sporozoite hepatocyte infection. Notably, monoclonal antibodies against PfCelTOS strongly inhibited oocyst development of P. falciparum and Plasmodium berghei expressing PfCelTOS in Anopheles gambiae mosquitoes. Taken together, our results demonstrate that anti-CelTOS responses elicited by vaccination or passive immunization can inhibit sporozoite and ookinete infection and impair vector transmission.

Efficacy of PermaNet\xae 3.0 and PermaNet\xae 2.0 nets against laboratory-reared and wild Anopheles gambiae sensu lato populations in northern Tanzania

BackgroundMosquitoes have developed resistance against pyrethroids, the only class of insecticides approved for use on long-lasting insecticidal nets (LLINs). The present study sought to evaluate the efficacy of the pyrethroid synergist PermaNet® 3.0 LLIN versus the pyrethroid-only PermaNet® 2.0 LLIN, in an East African hut design in Lower Moshi, northern Tanzania. In this setting, resistance to pyrethroid insecticides has been identified in Anopheles gambiae mosquitoes.MethodsStandard World Health Organization bioefficacy evaluations were conducted in both laboratory and experimental huts. Experimental hut evaluations were conducted in an area where there was presence of a population of highly pyrethroid-resistant An. arabiensis mosquitoes. All nets used were subjected to cone bioassays and then to experimental hut trials. Mosquito mortality, blood-feeding inhibition and personal protection rate were compared between untreated nets, unwashed LLINs and LLINs that were washed 20 times.ResultsBoth washed and unwashed PermaNet® 2.0 and PermaNet® 3.0 LLINs had knockdown and mortality rates of 100% against a susceptible strain of An. gambiae sensu stricto. The adjusted mortality rate of the wild mosquito population after use of the unwashed PermaNet® 3.0 and PermaNet® 2.0 nets was found to be higher than after use of the washed PermaNet® 2.0 and PermaNet® 3.0 nets.ConclusionsGiven the increasing incidence of pyrethroid resistance in An. gambiae mosquitoes in Tanzania, we recommend that consideration is given to its distribution in areas with pyrethroid-resistant malaria vectors within the framework of a national insecticide-resistance management plan.

Evidence of multiple insecticide resistance mechanisms in Anopheles gambiae populations in Bangui, Central African Republic

BackgroundKnowledge of insecticide resistance status in the main malaria vectors is an essential component of effective malaria vector control. This study presents the first evaluation of the status of insecticide resistance in Anopheles gambiae populations from Bangui, the Central African Republic.MethodsAnopheles mosquitoes were reared from larvae collected in seven districts of Bangui between September to November 2014. The World Health Organisation’s bioassay susceptibility tests to lambda-cyhalothrin (0.05%), deltamethrin (0.05%), DDT (4%), malathion (5%), fenitrothion (1%) and bendiocarb (0.1%) were performed on adult females. Species and molecular forms as well as the presence of L1014F kdr and Ace-1R mutations were assessed by PCR. Additional tests were conducted to assess metabolic resistance status.ResultsAfter 1 h exposure, a significant difference of knockdown effect was observed between districts in all insecticides tested except deltamethrin and malathion. The mortality rate (MR) of pyrethroids group ranging from 27% (CI: 19–37.5) in Petevo to 86% (CI: 77.6–92.1) in Gbanikola; while for DDT, MR ranged from 5% (CI: 1.6–11.3) in Centre-ville to 39% (CI: 29.4–49.3) in Ouango. For the organophosphate group a MR of 100% was observed in all districts except Gbanikola where a MR of 96% (CI: 90–98.9) was recorded. The mortality induced by bendiocarb was very heterogeneous, ranging from 75% (CI: 62.8–82.8) in Yapele to 99% (CI: 84.5–100) in Centre-ville. A high level of kdr-w (L1014F) frequency was observed in all districts ranging from 93 to 100%; however, no kdr-e (L1014S) and Ace-1R mutation were found in all tested mosquitoes. Data of biochemical analysis showed significant overexpression activities of cytochrome P450, GST and esterases in Gbanikola and Yapele (χ2 = 31.85, df = 2, P < 0.001). By contrast, esterases activities using α and β-naphthyl acetate were significantly low in mosquitoes from PK10 and Ouango in comparison to Kisumu strain (χ2 = 17.34, df = 2, P < 0.005).ConclusionsEvidence of resistance to DDT and pyrethroids as well as precocious emergence of resistance to carbamates were detected among A. gambiae mosquitoes from Bangui, including target-site mutations and metabolic mechanisms. The co-existence of these resistance mechanisms in A. gambiae may be a serious obstacle for the future success of malaria control programmes in this region.

Pupicidal Activity of Ethanol and Water Extracts of &lt;i&gt;Phytolacca dodecandra &lt;/i&gt; on &lt;i&gt; Anopheles gambiae&lt;/i&gt; (Diptera Culicidae) Pupae

Pupae are an integral part of Anopheles gambiae life history and a tool that effectively targets them is likely to impact on malaria vector density. In this study we evaluated pupicidal activities of crude ethanol and water extracts of Phytolacca dodecandra (L’ Herit) on An. gambiae (Diptera: Culicidae) under laboratory condition. Individual early pupae of An. gambiae mosquitoes were exposed to concentrations of 40, 20, 10, 5, 2.5 mgs/100 ml of mature green fruits and leaves of the shoot and midsection of P. dodecandra in containers measuring 6 cm top × 5.7 cm bottom × 3.5 cm height. P. dodecandra was sourced from Eldoret (highland) and Nyando (lowland). Extraction of P. dodecandra bioactives was done using 80% ethanol and distilled water. Extracts of Neem leaves and untreated rain water were used as positive and negative controls respectively. WHO, 2005 mortality threshold of >80% was used to determine the effectiveness of the extracts as pupicide 24 hours post exposure. Mortality of exposed pupae was dose dependent. Concentrations of 20 mgs/100 mls and higher and 40 mgs/ 100mls of mature green fruits from Nyando and Eldoret met the mortality threshold respectively. Extracts of P. dodecandra from Nyando was more potent than that from Eldoret as was water compared to ethanol extracts. Positive (Neem) control killed < 80% of exposed pupae. It was concluded that crude extracts of P. dodecandra are potent as pupicide against An. gambiae mosquitoes and is a likely alternative to synthetic insecticides against An. gambiae in future.

Knock down efficacy of commercially available insecticides against Anopheles gambiae

Abstract: Knockdown efficacy of commercial aerosol insecticides against laboratory reared Anopheles gambiae Kisumu strain mosquitoes and suppression of indoor resting density of An. gambiae complex mosquitoes in the field were investigated in the study. Laboratory reared 2-5 days old female An. gambiae mosquitoes were released into Peet-Grady chambers, sprayed with 0.3±0.1g of insecticides. Knock down rates were observed for one hour and mortality rates after 24hrs of spraying. Field efficacy studies were carried out by spraying houses with near uniform indoor resting densities of An. gambiae complex mosquitoes with aerosol insecticides and mosquitoes collected. Morphological and molecular characterization of mosquitoes was done. Probit analysis on knock down rates was carried out. Mortality rates and Mean indoor resting densities were compared using ANOVA in SPSS version 16. The KT50 and KT95 of Kenyan Baygon® and Kenyan raid® differed significantly with the other insecticides. Nigerian Baygon® achieved the lowest mortality rate of 87% and differed significantly (P0.05). Collected An. gambiae complex mosquitoes corresponded to An. arabiensis. The low knock down values by Kenyan Baygon®, Kenyan raid® and the low mortality rate by Nigerian Baygon® can be attributed to reduced efficacy rather than development of resistance. Whether the low deterrence of Anopheles gambiae complex mosquitoes into houses is due to development of pyrethroid insecticide resistance can be authenticated in another study. Key Words: Anopheles gambiae, Knock down time, Mortality rate, Indoor resting density.

Residual Effectiveness of Crude Ethanol Extracts of Mature Green Fruits of Endod &lt;i&gt;Phytolacca dodecandra&lt;/i&gt; (L Herit) against &lt;i&gt;An. gambiae&lt;/i&gt; (Diptera: Culicidae) Larvae

Mosquitoes are vectors of aborvirals and malaria and are a threat to public health. We evaluated residual effectiveness of crude ethanol extracts of Endod Phytolacca dodecandra (L’ Herit) leaves and mature green fruits in water against Anopheles gambiae (Diptera: Culicidae) larvae to determine duration of protection of the extract against An. gambiae mosquitoes. Stock’s solution of 80 mg/100 mls of crude ethanol extract of mature green fruits and leaves of Endod were prepared using rain harvested water and left to stand. Six such stocks’ solutions were prepared on six separate days. Each of the stock’s solutions was serially diluted to 40, 20, 10, 5 and 2.5 mg/100 ml and poured in five sets of separate plastic containers. Each container measuring 6 cm top × 5.7 cm bottom × 3.5 cm height contained a solution of a particular concentration. Twenty L3s were exposed per container. Extracts of Neem leaves and deltamethrin were used as positive and rain water alone as negative control. WHO threshold of>80% mortality was used to assess residual effectiveness. Mortality was determined after 24 hours. Resudual effectiveness was dose dependent. As low as 10 mg/100 mls solutions of freshly to two day old preparations of crude ethanol extract of mature green fruits and leaves of Endod killed more than 80% larvae. The solutions remained effective for three day only. Effectiveness reduced rapidly after day four. Crude ethanol extracts of Endod mature green fruits and leaves have a residual period of three days in water against An. gambiae larvae.

Insecticide Resistance in &lt;i&gt;Anopheles gambiae&lt;/i&gt; s.l Mosquitoes in Awka, Anambra State, Southeast Nigeria

Long-lasting insecticide nets (LLINs) and indoor residual spraying (IRS) are the main methods used for malaria vector control. However, the success of these methods has been hampered by the development and spread of insecticide resistance in major malaria vectors. The emergence of insecticide resistance in Anopheles mosquitoes in Nigeria has enormous implications for vector control interventions in the country. This study aimed to investigate the insecticide susceptibility levels of wild Anopheles gambiae mosquitoes from Southeast, Nigeria to the four main classes of insecticides used for vector control. Larval mosquitoes were collected from different breeding sites and reared in the insectary. Mosquitoes were identified morphologically and two to five day old adult female mosquitoes were used to conduct WHO susceptibility assays against pyrethroid (0.75% permethrin and 0.05% deltamethrin), organochlorine (4% DDT), organophosphate (0.25% pirimiphos-methyl) and carbamate (0.1% propoxur and 0.1% bendiocarb) insecticides. All mosquitoes collected were identified as members of the Anopheles gambiae s.l. The mosquitoes were completely susceptible to bendiocarb (100% mortality). Resistance to permethrin, pirimiphos-methyland DDT was recorded with percentage mortalities of 26.5%, 17.5% and 1.3% respectively. The KDT 50 recorded were 36.7 minutes (0.1% Bendiocarb), 39.8 minutes (0.1% propoxur), 50.9 minutes (0.05% deltamethrin), 91.4 minutes (0.75% permethrin), 116.3 minutes (0.25% Pirimiphos-Methyl) and 119.1 minutes (4% DDT). The results show that there is very high frequency of insecticide resistance in the study area and calls for a need for insecticide resistance management strategies to be implemented in the area.

Anopheles gambiae: Metabolomic Profiles in Sugar‐Fed, Blood‐Fed, and Plasmodium falciparum‐Infected Midgut

The mosquito midgut is a physiological organ essential for nutrient acquisition as well as an interface that encounters various mosquito‐borne pathogens. Metabolomic characterization would reveal biochemical fingerprints that are generated by various cellular processes. The metabolite profiles of the mosquito midgut will provide an overview of the biochemical events in both physiological states and the dynamic responses to pathogen infections. In this study, the midgut metabolic profiles of Anopheles gambiae mosquitoes following feeding with sugar, human blood, mouse blood, and Plasmodium falciparum-infected human blood were examined. A mass spectrometry system coupled to liquid and gas chromatography produced a time series of metabolites in the midgut at discrete conditions (sugar feeding, 24 h and 48 h post‐normal blood and P. falciparum-infected blood feeding). Triplicates were included to ensure system validity. A total of 512 individual compounds were identified; 511 were assigned to 8 superpathways and 75 subpathways. The dataset can be used for further inquiry into the metabolic dynamics of sugar and blood digestion and of malaria parasite infection. The dataset is accessible at the repository Dryad.

The ace-1 Locus Is Amplified in All Resistant Anopheles gambiae Mosquitoes: Fitness Consequences of Homogeneous and Heterogeneous Duplications.

Gene copy-number variations are widespread in natural populations, but investigating their phenotypic consequences requires contemporary duplications under selection. Such duplications have been found at the ace-1 locus (encoding the organophosphate and carbamate insecticides’ target) in the mosquito Anopheles gambiae (the major malaria vector); recent studies have revealed their intriguing complexity, consistent with the involvement of various numbers and types (susceptible or resistant to insecticide) of copies. We used an integrative approach, from genome to phenotype level, to investigate the influence of duplication architecture and gene-dosage on mosquito fitness. We found that both heterogeneous (i.e., one susceptible and one resistant ace-1 copy) and homogeneous (i.e., identical resistant copies) duplications segregated in field populations. The number of copies in homogeneous duplications was variable and positively correlated with acetylcholinesterase activity and resistance level. Determining the genomic structure of the duplicated region revealed that, in both types of duplication, ace-1 and 11 other genes formed tandem 203kb amplicons. We developed a diagnostic test for duplications, which showed that ace-1 was amplified in all 173 resistant mosquitoes analyzed (field-collected in several African countries), in heterogeneous or homogeneous duplications. Each type was associated with different fitness trade-offs: heterogeneous duplications conferred an intermediate phenotype (lower resistance and fitness costs), whereas homogeneous duplications tended to increase both resistance and fitness cost, in a complex manner. The type of duplication selected seemed thus to depend on the intensity and distribution of selection pressures. This versatility of trade-offs available through gene duplication highlights the importance of large mutation events in adaptation to environmental variation. This impressive adaptability could have a major impact on vector control in Africa.

Insecticide resistance in malaria vectors in Kumasi, Ghana.

BackgroundThere have been recent reports of surge in resistance to insecticides in pocketed areas in Ghana necessitating the need for information about local vector populations and their resistance to the insecticides approved by the World Health Organization (WHO). We therefore studied a population of malaria vectors from Kumasi in the Ashanti Region of Ghana and their resistance to currently used insecticides. We conducted susceptibility tests to the four major classes of insecticides by collecting larvae of anopheline mosquitoes from several communities in the region. Surviving adults from these larvae were then subjected to the WHO-approved susceptibility tests and characterization of knockdown resistance and acetylcholinesterase mutant genes.ResultsOut of 619 Anopheles specimens sampled, 537 (87%) were identified as Anopheles gambiae (sensu stricto), which was also the species with the lowest knockdown resistance mutant gene, 61% (P = 0.017). Knockdown resistance mutant gene was as high as 91% in An. coluzzii. Mosquitoes collected showed susceptibility ranging from 98–100% to organophosphates, 38–56% to carbamates and 15–47% and 38–46% to pyrethroids and organochlorides, respectively. The knockdown resistance mutation frequency of Anopheles gambiae (sensu lato) mosquitoes that were exposed to both pyrethroids and organochlorides was 404 (65%). Acetylcholinesterase mutant gene was not found in this population of vectors.ConclusionOur study shows that pyrethroids have the highest level of resistance in the population of mosquito vectors studied probably due to their frequent use, especially in impregnation of insecticide-treated nets and in insecticides used to control pests on irrigated vegetable farms. We recommend studies to monitor trends in the use of all insecticides and of pyrethroids in particular.

A Comparative Study of Anopheles Gambiae Male Mosquito’s Response to Frequency Modulated [FM] and Pulse Modulated [PM] Waves at Different Acoustic Frequencies and Distances

The efficiency of an electronic device meant to disrupt acoustic communication between male and female Anopheles gambiae mosquitoes was tested by recording approaches of the males towards the device as a function of distance and frequency. Different bioassays were conducted with broadcasts from the device and taped mimics of the female species wing beats at different distances and frequencies. A large number of the males, 85% remained near the broadcast speaker for a significantly longer period when the broadcast sounds of the device were at 380 Hz than at any other frequency range. The taped mimic sounds of the female mosquitoes in flight elicited a maximum response rate of 75 %. A test involving a choice between the device and taped sound mimics by male mosquitoes revealed that a high number (75 %) of them flew towards the device while 10% were attracted by the taped sounds whereas 15 % were undecided and made oscillatory motion between the two sources. Additional bioassays conducted to examine the effect of the device on non-flying males showed that almost 75 % were disturbed and approached the speaker within a distance of 0.5 m, which confirmed a radiative near-field communication for these insects.

West African Anopheles gambiae mosquitoes harbor a taxonomically diverse virome including new insect-specific flaviviruses, mononegaviruses, and totiviruses

Anopheles gambiae are a major vector of malaria in sub-Saharan Africa. Viruses that naturally infect these mosquitoes may impact their physiology and ability to transmit pathogens. We therefore used metagenomics sequencing to search for viruses in adult Anopheles mosquitoes collected from Liberia, Senegal, and Burkina Faso. We identified a number of virus and virus-like sequences from mosquito midgut contents, including 14 coding-complete genome segments and 26 partial sequences. The coding-complete sequences define new viruses in the order Mononegavirales, and the families Flaviviridae, and Totiviridae. The identification of a flavivirus infecting Anopheles mosquitoes broadens our understanding of the evolution and host range of this virus family. This study increases our understanding of virus diversity in general, begins to define the virome of a medically important vector in its natural setting, and lays groundwork for future studies examining the potential impact of these viruses on anopheles biology and disease transmission.

Prevalence of Plasmodium falciparum transmission reducing immunity among primary school children in a malaria moderate transmission region in Zimbabwe

Malaria continues to cause alarming morbidity and mortality in more than 100 countries worldwide. Antigens in the various life cycle stages of malaria parasites are presented to the immune system during natural infection and it is widely recognized that after repeated malaria exposure, adults develop partially protective immunity. Specific antigens of natural immunity represent among the most important targets for the development of malaria vaccines. Immunity against the transmission stages of the malaria parasite represents an important approach to reduce malaria transmission and is believed to become an important tool for gradual elimination of malaria. Development of immunity against Plasmodium falciparum sexual stages was evaluated in primary school children aged 6–16 years in Makoni district of Zimbabwe, an area of low to modest malaria transmission. Malaria infection was screened by microscopy, rapid diagnostic tests and finally using nested PCR. Plasma samples were tested for antibodies against recombinant Pfs48/45 and Pfs47 by ELISA. Corresponding serum samples were used to test for P. falciparum transmission reducing activity in Anopheles stephensi and An. gambiae mosquitoes using the membrane feeding assay. The prevalence of malaria diagnosed by rapid diagnostic test kit (Paracheck)™ was 1.7%. However, of the randomly tested blood samples, 66% were positive by nested PCR. ELISA revealed prevalence (64% positivity at 1:500 dilution, in randomly selected 66 plasma samples) of antibodies against recombinant Pfs48/45 (mean A 405nm=0.53, CI=0.46–0.60) and Pfs47 (mean A405nm=0.91, CI=0.80–1.02); antigens specific to the sexual stages. The mosquito membrane feeding assay demonstrated measurable transmission reducing ability of the samples that were positive for Pfs48/45 antibodies by ELISA. Interestingly, 3 plasma samples revealed enhancement of infectivity of P. falciparum in An. stephensi mosquitoes. These studies revealed the presence of antibodies with transmission reducing immunity in school age children from a moderate transmission area of malaria, and provide further support to exploit target antigens such as Pfs48/45 for further development of a malaria transmission blocking vaccine.

Decline in frequency of the 2La chromosomal inversion in Anopheles gambiae (s.s.) in Western Kenya: correlation with increase in ownership of insecticide-treated bed nets

BackgroundThe 2La chromosomal inversion, a genetic polymorphism in An. gambiae (sensu stricto) (s.s.), is associated with adaptation to microclimatic differences in humidity and desiccation resistance and mosquito behaviors. Ownership of insecticide-treated bed nets (ITNs) for malaria control has increased markedly in western Kenya in the last 20 years. An increase in the frequency of ITNs indoors could select against house entering or indoor resting of Anopheles mosquitoes. Thus, the frequency of the 2La inversion is postulated to change in An. gambiae (s.s.) with the increase of ITN ownership over time.MethodsAnopheles gambiae mosquitoes were sampled between 1994 and 2011 using pyrethrum knockdown, bednet traps and human landing catches (HLC) from Asembo and Seme, western Kenya. The 2La inversion was detected by a PCR assay with primers designed for proximal breakpoints of the 2La/a and 2L+a/+a chromosomal conformation. Mosquitoes were tested for malaria parasite infection by sporozoite ELISA.ResultsThe frequency of the 2La chromosomal inversion declined from 100 % of all chromosomes in 1994 to 17 % in 2005 and remained low through 2011 (21 %). ITN ownership increased from 0 to > 90 % of houses in the study area during this interval. The decline in the frequency of the 2La chromosomal inversion was significantly, negatively correlated with year (r = -0.93) and with increase in ITN ownership (r = -0.96). The frequency of the homo- and heterokaryotypes departed significantly from Hardy-Weinberg equilibrium, suggesting that 2La/a karyotype was under selection, earlier in its favor and later, against it. Precipitation and maximum monthly temperature did not vary over time, therefore there was no trend in climate that could account for the decline. There was no significant difference in frequency of the 2La inversion in An. gambiae (s.s.) females sampled indoors or outdoors in HCL in 2011, nor was there an association between the 2La inversion and infection with Plasmodium falciparum sporozoites.ConclusionsThe increase in ITN ownership in the study area was negatively correlated with the frequency of 2La inversion. The decline in 2La frequency in western Kenya is postulated to be due to differential impacts of ITNs on mosquitoes with different 2La karyotypes, possibly mediated by differences in behavior associated with the 2La karyotypes. Further research is required to determine if this is a widespread phenomenon, to further determine the association of the 2La karyotypes with mosquito behavior, and to assess whether ITNs are exerting selection mediated by differences in behavior on the different karyotypes.

Toxicology of potassium channel-directed compounds in mosquitoes

Potential targets for new vector control insecticides are nerve and muscle potassium channels. In this study, the activities of known potassium channel blockers (4-aminopyridine, quinidine, and tetraethylammonium) and the insecticide propoxur were compared to three experimental catechols and several other compounds against Anopheles gambiae and Aedes aegypti mosquitoes. Experimental catechol 1 was the most toxic experimental compound in all of the mortality assays conducted, but was at least 100-fold and 39-fold less toxic than propoxur against Ae. aegypti and An. gambiae, respectively. Injection treatment and synergist (piperonyl butoxide) bioassays found that catechol toxicity was not unduly impacted by cuticular transport or oxidative metabolism. Electrophysiological studies showed a decrease in amplitude of evoked muscle contractions, along with an increase in twitch duration at concentrations that increased basal muscle tension (mM). High concentration effects on basal muscle tension were matched by complete depolarization of the muscle membrane potential. Effects on muscle physiology and blockage of Kv2.1 potassium channels in patch clamp experiments were generally consistent with in vivo toxicity, except for 4-aminopyridine, which suggest the involvement of other potassium channel subtypes. Extensive melanization of Anopheles larvae, but not Aedes larvae, occurred from exposure to catechol compounds. Interaction with the phenol oxidase system within insects may be the cause of this melanization, but any contribution to toxicity requires further investigation.

Threat from Emerging Vectorborne Viruses

The earliest members of genus Homo were surely bedeviled by blood-feeding arthropods, some of which doubtless carried zoonotic pathogens. However, the phenomenon of vectorborne human epidemic disease began only after humans began building settlements 15,000 years ago (1). Settlements offered pathogens not only host density but also opportunities for their vertebrate reservoirs and arthropod vectors to cohabit with us. Epidemic Yersinia pestis (the Medieval Black Death) was only possible because black rats (Rattus rattus), the host of the vector flea, had become extraordinarily successful at living off human garbage and nesting in our buildings.