The importance of considering community-level effects when selecting insecticidal malaria vector products

BACKGROUND\ud \ud Insecticide treatment of nets, curtains or walls and ceilings of houses represent the primary means for malaria prevention worldwide. Direct personal protection of individuals and households arises from deterrent and insecticidal activities which divert or kill mosquitoes before they can feed. However, at high coverage, community-level reductions of mosquito density and survival prevent more transmission exposure than the personal protection acquired by using a net or living in a sprayed house.\ud \ud METHODS\ud \ud A process-explicit simulation of malaria transmission was applied to results of 4 recent Phase II experimental hut trials comparing a new mosaic long-lasting insecticidal net (LLIN) which combines deltamethrin and piperonyl butoxide with another LLIN product by the same manufacturer relying on deltamethrin alone.\ud \ud RESULTS\ud \ud Direct estimates of mean personal protection against insecticide-resistant vectors in Vietnam, Cameroon, Burkina Faso and Benin revealed no clear advantage for combination LLINs over deltamethrin-only LLINs (P = 0.973) unless both types of nets were extensively washed (Relative mean entomologic inoculation rate (EIR) ± standard error of the mean (SEM) for users of combination nets compared to users of deltamethrin only nets = 0.853 ± 0.056, P = 0.008). However, simulations of impact at high coverage (80% use) predicted consistently better impact for the combination net across all four sites (Relative mean EIR ± SEM in communities with combination nets, compared with those using deltamethrin only nets = 0.613 ± 0.076, P < 0.001), regardless of whether the nets were washed or not (P = 0.467). Nevertheless, the degree of advantage obtained with the combination varied substantially between sites and their associated resistant vector populations.\ud \ud CONCLUSION\ud \ud Process-explicit simulations of community-level protection, parameterized using locally-relevant experimental hut studies, should be explicitly considered when choosing vector control products for large-scale epidemiological trials or public health programme procurement, particularly as growing insecticide resistance necessitates the use of multiple active ingredients

Susceptibility status of mosquitoes (Diptera: Culicidae) to Malathion in Lagos, Nigeria

Mosquitoes are major vectors of infectious diseases transmitting malaria,&nbsp; lymphatic filariasis, yellow fever, dengue fever, zika and chikungunya virus.&nbsp; Resistance to DDT, pyrethriods and carbamates has been reported to different mosquito species in Nigeria. This investigation was carried out to determine the susceptibility status of mosquitoes in Lagos State, Nigeria to malathion. Mosquito larva were collected from four different Local Government Areas of Lagos, and reared to adult. Female adult mosquitoes were exposed to 5 % malathion insecticide test papers using WHO standard procedures and kits. Species identification was done using PCR assay. Suspected resistance was observed in Cx. quinquefasciatus from Kosofe and Alimosho with 24 hour mortality of 96 % and 95 % respectively. Other mosquito species and Cx. quinquefasciatus from Badagry and&nbsp; Ibeju-Lekki were fully susceptible 24 hours post exposure period. KDT50 and KDT95 for An. gambiae s.s ranges from 14.6 – 25.1 and 23.7 – 51.5 minutes respectively for all the location, KDT50 and KDT95 for Ae. aegypti ranges from 24.8 – 27.8 and 44.8 – 62.5 minutes respectively for all the location and KDT50 and KDT95 for Cx. quinquefasciatus ranges from 21.5 – 37.8 and 41.5 – 77.7 minutes respectively for all the location. The relatively high values of KDT50 and KDT95 in all assayed mosquito species call for urgent attention and may indicate the gradual development of malathion resistance to different mosquito species in Lagos. Regular insecticide resistance monitoring is needed and the indiscriminate use of unapproved organophosphate insecticides to be discouraged to forestall the development of malathion resistance in mosquitoes. Keywords: Mosquitoes, Insecticide resistance, Malathion, Organophosphates, Infectious disease

Impacts of Ivermectin Mass Drug Administration for Onchocerciasis on Mosquito Populations of Ogun State, Nigeria.

Abstract Background: This study investigated the impacts of single-dose mass drug administration (MDA) with ivermectin for onchocerciasis and lymphatic filariasis on mosquito populations in Ogun State, Nigeria. Methods: Mosquito samples were collected indoor and outdoor in two communities before and after MDA. The communities were pair-matched with two other control communities where concurrent mosquito collection was also carried out. The mosquitoes were identified by morphological features and parity status was determined by microscopy. The density and age structure of the mosquitoes were determined and compared between intervention and control communities. Environmental and climatic data of study locations were obtained from online databases. MDA treatment coverage survey was conducted in the treated communities. Results: Before MDA, the density of indoor Anopheles mosquitoes was 7.20 in the control communities. This was significantly lower (p = 0.049) in the intervention communities where the density was 1.43. The density of the indoor Anopheles population reduced significantly 2-3 days after MDA to 1.02 (p = 0.039) in the intervention communities. Parity rate also reduced significantly from 95.35 to 44.26 (p &lt; 0.001). The density of indoor Anopheles rebounded to 1.45 two weeks after MDA while parity rate remained significantly lower (p = 0.001) than before MDA. The density of indoor Culex increased 2-3 days after MDA from 0.07 to 0.10 (p = 0.527) and to 0.25 (p = 0.012) 13-14 days after MDA in the intervention communities. In Amini where MDA coverage was 65.9%, the indoor density of Anopheles reduced significantly from 0.90 to 0.33 (p = 0.005) 2-3 days after MDA while in Kugba-Ajagbe where MDA coverage was 41.0%, the reduction from 1.97 to 1.70 was not statistically significant (p = 0.446). Exposure to MDA across sampling intervals in the intervention communities showed a significant effect on the density (p &lt; 0.001) and parity rate (p = 0.003) of indoor Anopheles in the generalized linear model examining multiple factors. Conclusion: Ivermectin MDA showed a promising potential to impact on malaria transmission and Anopheles abundance at high MDA coverage.</jats:p

Impacts of ivermectin mass drug administration for onchocerciasis on mosquito populations of Ogun state, Nigeria

Abstract Background The impact of single-dose mass drug administration (MDA) of ivermectin for onchocerciasis on mosquito populations was investigated in Ogun State, Nigeria. Methods Indoor and outdoor collection of mosquitoes was carried out in two intervention (IC) and two control communities (CC) at three different periods: pre-MDA (baseline), 2–3 days after MDA and 13–14 days after MDA. The density and parity rate of female Anopheles and Culex mosquitoes were determined and compared. Environmental and climatic data of study locations were obtained to perform generalized linear model analysis. Results A total of 1399 female mosquitoes were collected, including 1227 Anopheles and 172 Culex mosquitoes. There was a similar magnitude of reduction in the indoor density of Anopheles by 29% in the IC and CC 2–3 days post-MDA but the reduction in indoor parity rate was significantly higher (p = 0.021) in the IC, reducing by more than 50%. In the IC, observation of a significant reduction at 2–3 days post-MDA was consistent for both the indoor density (1.43 to 1.02) and indoor parity rate (95.35% to 44.26%) of Anopheles mosquitoes. The indoor parity rate of Anopheles remained significantly reduced (75.86%) 13–14 post-MDA. On the other hand, the indoor density of Culex increased from 0.07 to 0.10 at 2–3 days post-MDA while the indoor parity rate of Culex did not change. The outdoor density of Anopheles in the IC increased (p = 0.394) from 0.58 to 0.90 at 2–3 days post-MDA; a similar observation was consistent for the outdoor density (2.83 to 3.90) and outdoor parity rate (70.59% to 97.44%) of Culex, while the outdoor parity rate of Anopheles reduced from 85.71 to 66.67% at 2–3 days post-MDA. A generalized linear model showed that ivermectin MDA significantly caused a reduction in both the indoor density (p &lt; 0.001) and indoor parity rate (p = 0.003) of Anopheles in the IC. Conclusion Ivermectin MDA resulted in the reduction of both the survival and density of Anopheles mosquitoes. This has strong implications for malaria transmission, which depends strongly on vector survival. Graphical abstract </jats:sec