An entomological survey and determination of vectoral infection rates for lymphatic filariasis in Ogoniland, Niger Delta, Nigeria
A combined field and laboratory investigation was conducted in five communities of Ogoniland to determine the status of lymphatic filariasis in relation to mosquito vectors for both dry and wet seasons of the year. The human bait method was employed twice weekly in the morning hours (6.00 am-7.30 am), and evening hours (6.00 pm- 8.30 pm), for collection of mosquitoes that probed into the skin using an aspirator. The mosquitoes collected were taken to the laboratory for identification, and dissected in 0.9% saline using standard procedure, while the microfilariae were identified using presence of sheath at their posterior region. The infection rate was obtained by expressing the percentage of the numbers positive against the numbers caught, while ATP of the mosquitoes were obtained using the values of microfilarial density, thus addition of monthly transmission potential (MTP) will give ATP of the vector species. Three mosquito species – A. gambiaesl, A. nili, and Culex p. fatigans, were identified as major vectors of the disease. The estimated annual vector biting and filarial prevalence rates for these mosquito species are 2, 220 and 22.2% for A. gambiae sl, 256 and 11.5% for A. nili and 7,747 and 24.3% for Culex p. fatigans. The mean microfilarial (mf) density in these vectors were 3.1 for A. gambiae sl, 0.6 for A. nili and 3.3. for Culex p. fatigans, with annual transmission potential (ATP) of 37, 4, and 50 for A. gambiae sl, A. nili, and Culex p. fatigans respectively. From the result of this study, it appears that Culex species showed greatest vectoral capacity in the transmission of lymphatic filariasis in the study area. The low microfilarial (mf) density in the human population, population density of the vectors and unsuitable ecological conditions may indicate a low endemicity of lymphatic filariasis in the study. The presence of this parasite may become health risk for the rural communities of the study area especially after a long period of infection.
Keywords: Lymphatic filariasis; mosquitoe; annual transmission potential.