Abstract
Bancroftian filariasis in Nigeria is endemic with 22.1% of the population thought to be infected. The main mosquito genera implicated with Wuchereria bancrofti transmission are Anopheles and Culex. The study was carried out to compare the infectivity rates of the vectors between the high transmission (rainy) and the low transmission (dry) seasons. Mosquitoes were sampled from houses and compared from six sentinel villages (3 each from Ohaukwu and Abakiliki Local Government Areas) of Ebonyi State, Nigeria. Day resting indoor collection (DRI) by Aspirator and Pyrethrum Spray Catch (PSC) were used to collect mosquitoes between 7:00 and 11:00am. After morphological identification, female parous mosquitoes were dissected in search for infective (L3) larvae of W. bancrofti. A total of 4,840 female mosquitoes were dissected. More mosquitoes were caught in the rainy season than in the dry season. Infectivity rates of vectors in Ohaukwu villages were 3.54 and 5.41% in the rainy and dry seasons, respectively, whereas in Abakiliki villages these were 1.85 and 1.19%, respectively. There was no significant difference in the overall infectivity rates between the two seasons in both Ohaukwu and Abakiliki villages (p>0.05). Similarly, no significant difference in the total/average transmission potentials were found between the seasons (p>0.05). Anopheles gambiae sl was the main vector in both study sites followed by an Anopheles funestus and Culex quinquefasciatus. There was a difference in infectivity rates of Anopheles species between the wet and dry seasons (p<0.05), whereas no significant difference exist in infectivity rates of Anopheles species and Cx. quinquefasciatus (p>0.05). Findings were discussed in the context of on-going plans to eliminate filariasis and the transmitting vectors. Key words: Bancroftian filariasis, rainy season, dry season, Wuchereria bancrofti. 
Highlights
Studies elsewhere have revealed that the peak transmission of filariasis was during the long rains and after the short rains in Mambru and Jaribuni villages of Kenya (Wijers and Kinyanjui, 1977)
The hot dry season transmission was interrupted in Mambru, but was rather low in Jaribuni
The Pyrethrum Spray Catch (PSC) and Mechanical Aspirator (MA) method records only the mosquitoes that rest indoors, it is widely used for estimating the abundance, seasonal densities, host preference and vector infection status as in this study
Summary
Wuchereria bancrofti which causes bancroftian filariasis is the only etiologic agent in Africa (Michael and Bundy, 1997).The disease is prevalent and widespread in Nigeria which is the third most endemic country in the world (after India and Indonesia) and estimated 22.1% of the population is thought to be infected (Eigege et al, 2003). Studies elsewhere have revealed that the peak transmission of filariasis was during the long rains and after the short rains in Mambru and Jaribuni villages of Kenya (Wijers and Kinyanjui, 1977). Wijers and Kaleli (1984) in related study concluded that transmission season coincides with the long rain during which filariasis vectors were in abundance. No clear reports on comparison between vector infectivity rates between the seasons were shown
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