Mosquito electrocuting traps for directly measuring biting rates and host-preferences of Anopheles arabiensis and Anopheles funestus outdoors

Deodatus F. Maliti,Amos T. Mlwale,Nicodem J. Govella,Nosrat Mirzai,Katharina S. Kreppel,Felician C. Meza,Gerry F. Killeen,Heather M. Ferguson

doi:10.1186/s12936-019-2726-x

Deodatus F. Maliti, Amos T. Mlwale + Show 6 more

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https://doi.org/10.1186/s12936-019-2726-x

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Abstract

BackgroundMosquito biting rates and host preferences are crucial determinants of human exposure to vector-borne diseases and the impact of vector control measures. The human landing catch (HLC) is a gold standard method for measuring human exposure to bites, but presents risks to participants by requiring some exposure to mosquito vectors. Mosquito electrocuting traps (METs) represent an exposure-free alternative to HLCs for measuring human exposure to malaria vectors. However, original MET prototypes were too small for measuring whole-body biting rates on humans or large animals like cattle. Here a much larger MET capable of encompassing humans or cattle was designed, and its performance was evaluated relative to both the original small MET and HLC and for quantifying malaria vector host preferences.MethodsHuman landing catch, small human-baited METs (MET-SH), and large METs baited with either a human (MET-LH) or calves (MET-LC) were simultaneously used to capture wild malaria vectors outdoors in rural southern Tanzania. The four capture methods were compared in a Latin-square design over 20 nights. Malaria vector host preferences were estimated through comparison of the number of mosquitoes caught by large METs baited with either humans or cattle.ResultsThe MET-LH caught more than twice as many Anopheles arabiensis than either the MET-SH or HLC. It also caught higher number of Anopheles funestus sensu lato (s.l.) compared to the MET-SH or HLC. Similar numbers of An. funestus sensu stricto (s.s.) were caught in MET-LH and MET-SH collections. Catches of An. arabiensis with human or cattle-baited large METs were similar, indicating no clear preference for either host. In contrast, An. funestus s.s. exhibited a strong, but incomplete preference for humans.ConclusionsMETs are a sensitive, practical tool for assessing mosquito biting rates and host preferences, and represent a safer alternative to the HLC. Additionally these findings suggest the HLC underestimate whole-body human exposure. MET collections indicated the An. funestus s.s. population in this setting had a higher than expected attack rate on cattle, potentially making eliminating of this species more difficult with human-targetted control measures. Supplementary vector control tools targetted at livestock may be required to effectively tackle this species.

Highlights

Mosquito biting rates and host preferences are crucial determinants of human exposure to vectorborne diseases and the impact of vector control measures
This study evaluated the performance of a new Mosquito electrocuting traps (METs) prototype designed to be capable of encompassing entire hosts, and evaluated its performance relative to human landing catch (HLC) and the original small sized MET for measuring human exposure to malaria vectors
The proportion of An. funestus s.l. whose DNA could be successfully amplified varied between trapping methods as follows: HLC = 61% (ntotal = 297), METSH = 49% (ntotal = 546), MET-LH = 51% (ntotal = 39) and large cattle-baited mosquito electrocuting trap (MET-LC) = 56% (ntotal = 484)

Summary

Introduction

Mosquito biting rates and host preferences are crucial determinants of human exposure to vectorborne diseases and the impact of vector control measures. Accurate estimation of mosquito biting rates and host preference are critical for assessing exposure risks of humans and animals to vector-borne diseases, and for optimizing the impact of vector control strategies [1,2,3,4]. Until relatively recently, measuring human exposure to mosquito bites outdoors necessitated laborious, potentially hazardous and ethically questionable human landing catches (HLCs) [5,6,7]. Despite these risks, the HLC remains the only technique considered reliable for direct estimation of human exposure to mosquito bites inside houses and outdoors, and over the course of the entire night [6, 8]. Given the importance of measuring malaria transmission, there is a great need for surveillance tools that can accurately measure total human exposure to mosquito bites in both indoor and outdoor settings

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