Successful interruption of the transmission of Onchocerca volvulus in Mpamba-Nkusi focus, Kibaale district, mid-western Uganda

Background: The Mpamba-Nkusi onchocerciasis focus is situated in the mid-western part of Uganda. It has an area of 300 km2 and used to have Simulium neavei as the vector which develops in a phoretic association on freshwater crabs. Ground larviciding with temephos (Abate EC500) was initiated in June 2002. All the 330 communities in this focus have undergone annual treatment with ivermectin since 1995 and were later shifted to semi-annual treatment in 2009.Objective: To establish the impact of mass drug administration in combination with larviciding on the interruption of O. volvulus transmission.Design: Longitudinal studySetting: Rural areas in Mpamba-Nkusi focus, Kibaale district.Subjects: Individuals five years and above living in the focus.Interventions: Annual and semi-annual treatment with ivermectin supplemented by vector elimination were used. Epidemiological, entomological and serological assessments were conducted.Results: Freshwater crabs (n = 14,391) caught from monitoring sites (n = 41) since 2008 were negative for immature stages of S. neavei. The S.neavei population was reduced following trial and initiation of ground larviciding. No adult S. neavei has been caught in the focus for over five years. Parasitological examination of individuals residing in the focus revealed a microfilaria (mf) prevalence of 0.3% (95% CI 0 – 0.65%; n = 732) in 2012. Serological assays testing for Onchocerca volvulus antibodies conducted on 3351 children <15 years in 2009 indicated point prevalence of 0.6% , (95% CI, 0.3-0.8%) while in 2012 another survey conducted among 3,407 children, only 1/3407 (0.03%, 95% CI, 0-0.09%) individual was positive for O. volvulus antibodies.Conclusions: Epidemiological and entomological findings suggest that interruption of transmission has been achieved

Reduced susceptibility to pyrethroid insecticide treated nets by the malaria vector Anopheles gambiae s.l. in western Uganda

<p>Abstract</p> <p>Background</p> <p>Pyrethroid insecticide-treated mosquito nets are massively being scaled-up for malaria prevention particularly in children under five years of age and pregnant mothers in sub-Saharan Africa. However, there is serious concern of the likely evolution of widespread pyrethroid resistance in the malaria vector <it>Anopheles gambiae s.l</it>. due to the extensive use of pyrethroid insecticide-treated mosquito nets. The purpose of this study was to ascertain the status of pyrethroid resistance in <it>An. gambiae s.l</it>. in western Uganda.</p> <p>Methods</p> <p>Wild mosquitoes (1–2 days old) were exposed in 10 replicates to new nets impregnated with K-othrine (Deltamethrin 25 mg/m²), Solfac EW50 (Cyfluthrin 50 mg/m²) and Fendona 6SC (Cypermethrin 50 mg/m²) and observed under normal room temperature and humidity (Temperature 24.8°C���27.4°C, Humidity 65.9–45.7). A similar set of mosquitoes collected from the control area 80 km away were exposed to a deltamethrin 25 mg/m²impregnated net at the same time and under the same conditions. The 10-year mean KDT₅₀and mortality rates for each of the three pyrethroid insecticides were compared using the Student <it>t</it>-test.</p> <p>Results</p> <p>A significant increase in the mean knockdown time (KDT₅₀) and mean mortality rate were observed in almost all cases an indication of reduced susceptibility. The overall results showed a four-fold increase in the mean knockdown time (KDT₅₀) and 1.5-fold decrease in mortality rate across the three pyrethroid insecticides. There was a significant difference in the 10-year mean KDT₅₀between deltamethrin and cyfluthrin; deltamethrin and cypermethrin, but no significant difference between cyfluthrin and cypermethrin. The 10-year mean difference in KDT50 for mosquitoes exposed to deltamethrin from the control site was significantly different from that of mosquitoes from the intervention site (p<0.05, t=3.979, 9df). The 10-year mean difference in mortality rate between deltamethrin (84.64%); cyfluthrin (74.18%); cypermethrin (72.19%) and the control (90.45%) showed a significant decline in mortality across all the three insecticides.</p> <p>Conclusion</p> <p>Generally the results showed a trend of increase in mosquito resistance status with cross-resistance against all the three pyrethroid insecticides. This study reveals for the first time the development of pyrethroid resistance in <it>An. gambiae s.l</it>. in Western Uganda. It is therefore strongly recommended that the impact of this development on malaria control efforts be closely monitored and alternative fabric treatments be considered before this problem curtails community wide implementation of this malaria control strategy in Uganda.</p