Entomological surveillance in the context of malaria elimination in some selected sentiniel sites of Ethiopia

Abstract

Introduction: Following the comandable progress made on malaria control programme so far, Ethiopia is persuing malaria elimination in 239 selected low transmission districts located in 6 different regions. Of these, 50 districts has been selected for elimination of local transmission of falciparum malaria based on standard WHO customized criteria.
Objective: The objective of this study was to generate evidence to allow policy making for optimal malaria vector control in the eight districts targeted for elimination by the national malaria control program (NMCP) of Ethiopia.
Method: Eight sentinel sites were selected from four regional states (Oromia, Amhara, SNNPR and Tigray) and one city administration (Diredawa). Entomological surveillance was conducted for two months (November and December 2017). Mosquitoes were collected using human landing collection (HLC), light trap catches (LTCs), pyrethrum spray catches (PSCs) and pitfall shelter (PFSs). Larval collection were made using standard dip. Over all 14,471 mosquitoes were collected by all collection methods (HLCs, LTCs, PSCs, and PFS) from eight sentinel sites.
Results: Of the 14,471 mostquitoes, 946 were anopheline and 13,525 were culicine mosquitoes. Of the 946 Anopheline mosquitoes, An. gambiae s.l. comprised the majority (67.8%) followed by An. coustani (22.4%). The rest Anophelines (An. pharoensis,An. demilloni, An. squamosus, An. funestus, An. cenerus, An. pretoriensis and An.maculipalpis) comprised 11.8%. The proportion of anopheline mosquitoes collected outdoor by HLC was significantly higher (p < 0.001) compared to indoor collection. All anophelines showed early peak biting activity (18:00h to 23:00h) both indoor and outdoor in all study sites. There was significant difference in mosquito population density (p < 0.001) across the sentinel sites, between sites Kalu (0.48/night/person-hour), Legehare (0.38/night/person-hour) and Kebena (0.16/night/person-hour). A total of 352 and 139 anopheline mosquito larvae were collected from Kebena and Merti, respectively. Of this, the mean density of An. gambiae s.l larvae in Kebena and Merti site was documented as 41.9 ± 12.0, and.7 ± 6.2, respectively. 

Conclusion: Higher anopheline mosquito densities were recorded outdoor than indoor. This may sustain outdoor or residual transmission and could be challenging for malaria elimination efforts in these sites. Given the evidence of peak biting activity in the early part of the night before people go to bed; existing interventions methods in particular use of LLINs alone may not be helpful for effective vector control. Thus, new or alternative vector control intervention tools which targets outdoor resting, outdoor and early biting malaria vectors should be developed and implemented as a component of integrated vector management (IVM) to sustain malaria control and enhance elimination efforts.