Bio-efficacy of long-lasting insecticidal nets against Anopheles gambiae mosquito after four years of usage in Mikang, Plateau State, Nigeria

Insecticide-treated nets (ITN) and Indoor residual spraying (IRS) are key components in malaria control through reliance on susceptibility of Anopheles vector mosquitoes to chemical insecticides in bed nets and for IRS. Bio- efficacy of long-lasting insecticidal nets (LLINs) of various years of usage on populations of An. gambiae was investigated in Mikang LGA of Plateau State, Nigeria. About 2-3 days old non-blood fed adult An. gambiae mosquitoes reared from larvae were tested with LLINs that had been in use for 1-4 years using the standard WHO cone test. Bio-efficacy of LLINs decreased with age of the nets tested. Knockdown of mosquitoes were 90 (100%), 87 (96.7%), 86 (95.6%), 56 (62.0%) and 36 (40.0%) in control nets ages 0, 1, 2, 3 and 4 years respectively. Significant difference was observed between the control and the other net age groups while no significant difference (p<0.05)was observed between the knockdown rates for net age 1 and 2 and those in use for 3 and 4 years suggesting insecticide decay as nets age. In the current study 100% mortality after 24 hours post exposure was observed in adult mosquitoes from control nets and those in use for 1-4 years, indicating susceptibility. There was significant difference in the susceptibility of mosquitoes to different nets.LLINs should be monitored for pyrethroids resistance as they age and preferably, they should be replaced after every two years of use. Keywords : Malaria; pyrethroid; insecticide decay; bio-efficacy; susceptibility.