Effect of indoor residual spraying and use of long-lasting insecticide-treated nets on anopheles mosquito biting, infectivity and species composition in Nagongera, Tororo, Uganda
Musiime, Kashaija Alex
MetadataShow full item record
Long lasting insecticidal nets (LLINs) and indoor residual spraying of insecticide (IRS) are widely recommended for the prevention of malaria in endemic regions. Data from human landing catches provide information on the impact of vector control on vector populations. Here we compared malaria transmission indoors and outdoors, before and after mass deployment of LLINs and IRS in Uganda. The study took place in Tororo district, a historically high transmission area where universal LLINs distribution was conducted in November 2013 and May 2017 and six rounds of IRS implemented from December 2014 to July 2018. Human landing catches were performed in eight houses monthly from October 2011 to September 2012 (pre-intervention period) and every four weeks from November 2017 to October 2018 (post-intervention period). Mosquitoes were collected outdoors from 6:00 p.m. to 10:00 p.m. and indoors from 6:00 p.m. to 06:00 a.m. Female Anopheles were tested for the presence of Plasmodium falciparum sporozoites and species identification performed using gross dissection and Polymerase Chain Reactions (PCR). The interventions were associated with a decline in human biting rate from 19.6 to 2.3 female Anopheles mosquitoes per house per night (p < 0.001) and annual entomological inoculation rate from 129 to 0 infective bites per person per year (p < 0.001). The proportion of mosquitoes collected outdoors increased from 11.6% to 49.4% (p < 0.001). Prior to the interventions the predominant species was An. gambiae s.s., which comprised an estimated 76.7% of mosquitoes. Following the interventions, the predominant species was An. arabiensis, which comprised 99.5% of mosquitoes, with almost complete elimination of An. gambiae s.s. (0.5 %). Mass distribution of LLINs and six rounds of IRS dramatically decreased vector density and sporozoite rate resulting in a marked reduction in malaria transmission intensity in a historically high transmission site in Uganda. These changes were accompanied by a shift in vector species from An. gambiae s.s. to An. arabiensis and a relative increase in outdoor biting.