Proof-of-Principle for implementation of ground larviciding in the Nkam- Wouri river basin in Cameroon: Simulium larval susceptibility to temephos and effect of ten weeks treatment of the Mbende tributary on larval density and simulium biting rate

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Abstract Background Onchocerciasis transmission in some endemic foci has been persistent despite over 18 years of annual ivermectin mass drug administration (Ivm-MDA). Several reasons including poor adherence to ivermectin intake due to fear of severe adverse events (SAEs) in areas of co-infection with loiasis and the presence of numerous breeding sites enhancing abundant vector population contribute to this persistent transmission. The change in paradigm from onchocerciasis control to elimination may not be achieved if alternative control measures are not used. There is therefore a need to complement Ivm-MDA with other strategies like vector control. In this study, we experimented the effect of ten weeks ground larviciding with temephos on the larval density and vector population. Method Black flies breeding sites along the course of rivers within the study area were identified. Susceptibility test was done on freshly collected larvae by exposing them to different concentrations of temephos and assessing mortality rates. Flies were collected at two points (Mbende and Dimbong) to determine the biting density. Fishing was used to assess vertebrate aquatic fauna at river Mbende while invertebrate fauna was assessed during collection of larvae as they are usually found on same substrate as the larvae. Ground larviciding was done using the spraying method at two dosing points. Results Six breeding sites were identified with larvae of Simulium species. As the concentration of temephos was decreasing (0.1 to 0.001Mg/L), the mortality of larvae also decreased with a 100% mortality observed at concentrations between 0.1 to 0.025 Mg/L. The non-target fauna included various fish species, crabs, crayfish, and invertebrate fauna. Simulium larvae were totally cleared from their breeding sites and there was a steady reduction in the biting density at the collection point from week 1 through week 10 with biting rate as high as 900 flies/man/day at the beginning to 180 flies/man/day at the end of ground larviciding. Conclusion Simulium larvae in the study area are susceptible to temephos. Total clearance of larvae and visible reduction (82.8%) in the Simulium biting density were observed during the study.

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