Preliminary studies on human lymphatic filariasis transmission control trials using Insecticide Treated Bednet (ITBN) in parts of Imo State, Nigeria

Abstract

Human lymphatic filariasis (LF) is a significant public health problem in many tropical and sub tropical countries resulting in disfigurement and disability which warrants preventive action. The effectiveness of insecticide-treated bednet (ITBN) was compared in selected sentinel villages of Imo State, Nigeria, between February 2009 and December 2011, to evaluate their potential for LF control. Two cohorts were used; ITBN-full coverage/wide scale use and ITBN-vulnerable coverage/ selective use. Endophilic mosquitoes caught twice a month by pyrethrum spray catch (PSC) and day resting indoor collection (DRI) with aspirator were identified using standard morphological keys. Of 8,349 engorged female mosquitoes dissected/ examined for parity infection/infectivity status with Wuchereria bancrofti larvae, 60.88% (5,088/8,349) and 39.12% (3,266/8,349) represented ITBN-vulnerable and ITBN-full coverage catches respectively. Overall, ITBN-vulnerable cohorts collections were insignificantly higher than ITBN-full coverage cohorts (62.31% versus 37.69%, 59.22% versus 40.73%, 62.22% versus 37.78%) for 2009, 2010 and 2011 respectively. Five species present in both cohorts comprised Anopheles gambiae s.l., the most abundant (85.19% versus 74.04%), An. funestus s.l. (8.42% versus 12.19%) and Cx. quinquefasciatus (5.88% versus 3.83%) while Aedes aegypti and Mn. africana were rarely present. Village-specific vector densities/relative abundance from ITBN-vulnerable cohorts and ITBN-full cohorts showed no significant difference (p>0.05). Similarly, the physiological, infection (0.18% versus 0.49%) and infectivity status (0.00% versus 0.00%) were insignificant between the cohorts (p>0.05). The study highlights the importance of integrating vector borne disease interventions in the on-going plan to eliminate LF and the transmitting mosquito vectors in Nigeria.

Keywords: Lymphatic filariasis; ITBN-full household coverage; ITBN-vulnerable household coverage; W. bancrofti; vectors