Entomological Evaluation of Malaria Vectors at Different Altitudes in Hai District, Northeastern Tanzania

Abstract

Entomological monitoring in four villages situated along an altitude transect in the Hai District of Northeastern Tanzania identified Anopheles arabiensis Patton as the principal vector of malaria and detected seasonal changes in vector behavior. Over a 13-mo sampling period, 10,557 mosquitoes were collected with CDC light traps, pyrethrum spray catches, and pit traps of which 5,969 (56.5%) wereAn. arabiensis, 762 (7.2%) wereAnopheles funestus Giles s.l., 3,578 (33.9%) were culicines, and 248 (2.3%) were nonvector anophelines. Vector densities declined rapidly with increasing altitude, demonstrating a 50% decrease in annual human biting rate for every 86-m rise in altitude. Light traps were found to be more efficient than spray catches for the collection of An. arabiensis. This observation was attributed to increased exophily of this species, most notably in the wet season, and is supported by seasonal changes in the human blood index and fed/gravid ratio. These results indicate that spray catches may underestimate the abundance of exophilic vectors such as An. arabiensis and that entomological monitoring may require more than one collection method, especially at low vector densities. The annual entomological inoculation rate (EIR) decreased sharply with increasing altitude, with large variation around the estimate at low vector densities. Increased transmission because of unpredictable short rains at low altitudes and spatial clustering of infective mosquitoes may contribute to elevated EIR estimates.

Altitude‐Dependent and ‐Independent Variations inPlasmodium falciparumPrevalence in Northeastern Tanzania

“…In coastal Tanga, the principal vectors are Anopheles gambiae (sensu stricto) and Anopheles funestus [10], whereas, around Mt. Kilimanjaro, vectors are almost exclusively Anopheles arabiensis [38,39], which is a significantly less efficient vector than A. gambiae (sensu stricto) [40]. All 3 vectors are present at various times throughout the year in the Pare Mountains [41].…”

Malaria entomological profile in Tanzania from 1950 to 2010: a review of mosquito distribution, vectorial capacity and insecticide resistance

“…north, north-east and east. From early 1960s to 1985 all research activities on malaria vectors were almost concentrated in Tanga (Gillies and Wilkes, 1965 ;Balirwa, 1975;Lines et al, 1987;Magesa et al, 1991;Wilkes et al, 1995;Mboera et al, , 2010Temu et al, 1998;Malima, 1999;Braimah et al, 2005;Kulkarni et al, 2006a;Kigadye et al, 2010). Majority of the articles indicated the occurrence of An.…”

“…There is need therefore to revitalize more work on this area which is important in assessing the impact of malaria control interventions. Similarly, only 8.4% of the reviewed studies estimated the entomological inoculation rate (EIR), highlighting the paucity of such important information in Tanzania (Temu et al, 1998;Ijumba et al, 2002;Bodker et al, 2003;Kulkarni et al, 2006a). "Available EIRs value ranges from 0.03-299.3 infective bites per person per year for An.…”

“…funestus (Temu et al, 1998;Ijumba et al, 2002;Bodker et al, 2003;Kulkarni et al, 2006a;Mboera et al, 2007Mboera et al, , 2010; 2.0 -6241 for An. arabiensis (Mnzava 1991;Temu et al, 1998;Ijumba et al, 2002;Kulkarni et al, 2006a); 0.05 -1022 for An. gambiae s.s. (Mnzava 1991;Temu, et al, 1998;Bodker, et al, 2003); 18.3 for An.…”

“…This has led to the estimation of the degree of degree of anthropophily through the human blood index (HBI). Several studies in Tanzania have documented the host preference of malaria vectors (Temu et al, 1998;Ijumba et al, 2002;Bodker et al, 2003;Kulkarni, et al, 2006a). The documented Human Blood Index (HBI) for An.…”