Bloodmeal sources and feeding behavior of anopheline mosquitoes in Bure district, northwestern Ethiopia

Background Mosquito bloodmeal sources determine the feeding rates, adult survival, fecundity, hatching rates, and developmental times. Only the female Anopheles mosquito takes bloodmeals from humans, birds, mammals, and other vertebrates for egg development. Studies of the host preference patterns in blood-feeding anopheline mosquitoes are crucial to determine malaria vectors. However, the human blood index, foraging ratio, and host preference index of anopheline mosquitoes are not known so far in Bure district, Ethiopia. Methods The origins of bloodmeals from all freshly fed and a few half-gravid exophagic and endophagic females collected using Centers for Disease Control and Prevention light traps were identified as human and bovine using enzyme-linked immunosorbent assay. The human blood index, forage ratio, and host feeding index were calculated. Results A total of 617 specimens belonging to An. arabiensis (n = 209), An. funestus (n = 217), An. coustani (n = 123), An. squamosus (n = 54), and An. cinereus (n = 14) were only analyzed using blood ELISA. Five hundred seventy-five of the specimens were positive for blood antigens of the host bloods. All anopheline mosquitoes assayed for a bloodmeal source had mixed- rather than single-source bloodmeals. The FR for humans was slightly > 1.0 compared to bovines for all Anopheles species. HFI for each pair of vertebrate hosts revealed that humans were the slightly preferred bloodmeal source compared to bovines for all species (except An. squamosus), but there was no marked host selection. Conclusions All anopheline mosquitoes assayed for bloodmeal ELISA had mixed feeds, which tends to diminish the density of gametocytes in the mosquito stomach, thereby reducing the chance of fertilization of the female gamete and reducing the chances of a malaria vector becoming infected. Moreover, An. coustani was the only species that had only human bloodmeals, meaning that this species has the potential to transmit the disease. Therefore, combination zooprophylaxis should be reinforced as a means of vector control because the study sites are mixed dwellings.

Anopheles arabiensis hotspots along intermittent rivers drive malaria dynamics in semi-arid areas of Central Ethiopia

Background Understanding malaria vector’s population dynamics and their spatial distribution is important to define when and where the largest infection risks occur and implement appropriate control strategies. In this study, the seasonal spatio-temporal dynamics of the malaria vector population and transmission intensity along intermittent rivers in a semi-arid area of central Ethiopia were investigated. Methods Mosquitoes were collected monthly from five clusters, 2 close to a river and 3 away from a river, using pyrethrum spray catches from November 2014 to July 2016. Mosquito abundance was analysed by the mixed Poisson regression model. The human blood index and sporozoite rate was compared between seasons by a logistic regression model. Results A total of 2784 adult female Anopheles gambiae sensu lato (s.l.) were collected during the data collection period. All tested mosquitoes (n = 696) were identified as Anopheles arabiensis by polymerase chain reaction. The average daily household count was significantly higher (P = 0.037) in the clusters close to the river at 5.35 (95% CI 2.41–11.85) compared to the clusters away from the river at 0.033 (95% CI 0.02–0.05). Comparing the effect of vicinity of the river by season, a significant effect of closeness to the river was found during the dry season (P = 0.027) and transition from dry to wet season (P = 0.032). Overall, An. arabiensis had higher bovine blood index (62.8%) as compared to human blood index (23.8%), ovine blood index (9.2%) and canine blood index (0.1%). The overall sporozoite rate was 3.9% and 0% for clusters close to and away from the river, respectively. The overall Plasmodium falciparum and Plasmodium vivax entomologic inoculation rates for An. arabiensis in clusters close to the river were 0.8 and 2.2 infective bites per person/year, respectively. Conclusion Mosquito abundance and malaria transmission intensity in clusters close to the river were higher which could be attributed to the riverine breeding sites. Thus, vector control interventions including targeted larval source management should be implemented to reduce the risk of malaria infection in the area.

Blood Meal Sources and Feeding Behavior of Anophelines Mosquitoes in Bure District, Northwestern Ethiopia

Background: Mosquito blood meal sources determine their own feeding rates, adult survival, fecundity, hatching rates, and developmental times. The only female Anopheles mosquito takes blood meals from humans, birds, mammals, or other vertebrate animals for egg development. Studies of host preference patterns in blood-feeding anopheline mosquitoes are crucial to incriminating malaria vectors. However, the human blood index, foraging ration, and host preference index of anophelines mosquitoes were not known so far in Bure district Ethiopia.Methods: The origin of blood meals from all freshly fed and a few half-gravid exophagic and endophagic females collected using the center for disease control and prevention light trap catches were identified as human and bovine using Enzyme Linked Immune Sorbent Assay. Human blood index, forage ratio, and host feeding index were calculated.Results: A total of 617 specimens belonging to An. arabiensis (n = 209), An. funestus (n= 217), An. coustani (n= 123), An. squamosus (n= 54) and An. cinereus (n= 14) were only analyzed for blood ELISA. 577 of the overall specimens were positives for blood antigens of the host bloods. All anopheline mosquitoes assayed for blood meal sources had extremity mixed blood meals sources than single blood meals. The FR for a human was slightly > 1.0 than bovine for all Anopheles species. HFI for each pair of vertebrate hosts revealed that humans was a bit preferred blood meal source to bovine for all species (except An. squamosus), but did not exhibit a marked host selection.Conclusions: All assayed anopheline mosquitoes for blood meal ELISA had a mixed feed which tends to diminish the density of gametocytes in the mosquito stomach, thereby reducing the chance of fertilization of the female gamete and reduce the chances of malaria vector becoming infected. Moreover, An. coustani was the only species that had only human blood meal alone mean that this species has a potential to transmit the disease. Therefore, combination zooprophylaxis should be reinforced as a means of vector control because the study sites are mixed dwelling.

A systematic review and meta-analysis of the human blood index of the major African malaria vectors

BACKGROUNDThe proportion of mosquito blood-meals that are of human origin, referred to as the ‘human blood index’ or HBI, is a key determinant of malaria transmission. We conducted a systematic review of the HBI for the major African malaria vectors.RESULTSEvidence is presented for higher HBI among Anopheles gambiae (M/S forms and An. coluzzii/An. gambiae s.s. are not distinguished for most studies and therefore combined) as well as An. funestus when compared with An. arabiensis (prevalence odds ratio adjusted for collection location [i.e. indoor or outdoor]: 1.62; 95%CI 1.09-2.42; 1.84; 95%CI 1.35-2.52, respectively). This finding is keeping with the entomological literature which describes An. arabiensis to be more zoophagic than the other major African vectors. However, analysis also revealed that HBI was more associated with location of mosquito captures (R2=0.29) than with mosquito (sibling) species (R2=0.11).CONCLUSIONSOur findings call into question the appropriateness of current methods of assessing host preferences among disease vectors and have important implications for strategizing vector control.

Lymphatic filariasis in the coastal areas of Digha, West Bengal, India

The state of West Bengal, India, has a long coastline with the Bay of Bengal. No information exists regarding filarial epidemiology and its vector in these coastal areas. The present study was designed to assess the epidemiology of lymphatic filariasis and the role of available mosquitoes as its vector in eight coastal villages around Digha, West Bengal. Night blood samples of 4016 individuals were collected and each of them was examined clinically for any manifestations of the disease. Overall, microfilaria rate, mean microfilarial density and disease rate were 9.06%, 8.63% and 7.72%, respectively. The causative parasite was identified as Wuchereria bancrofti and Culex quinquefasciatus was incriminated as the vector responsible. Vector infection and infectivity rates were assessed to be 12.5% and 0.73%, respectively. The human blood index of human-house-frequenting vector population was 70%. Vector density, vector infection, infectivity rates and human blood index were higher in the rainy season in the study area. Overall, the filarial situation was bad and, as a measure, single-dose diethylcarbamazine citrate (6 mg/kg body weight) treatment was given to all the microfilariaemic patients. Night blood samples of the treated individuals were tested for microfilariae on days 10 and 365, which revealed interesting results.