Characterisation of human exposure to nocturnal biting by malaria and arbovirus vectors in a rural community in Chókwè district, southern Mozambique

Abstract

Background: Understanding the magnitude of human exposure to mosquito biting is fundamental to reduce pathogen transmission. Here we report on a study quantifying the levels of mosquitoes attacking humans throughout the night in a rural area of Southern Mozambique. Methods: Surveys were carried out in Massavasse village, southern Mozambique. The abundance and composition of host-seeking mosquito communities at night were assessed by human-landing catches (HLC) at one-hour intervals. Periods when people were located predominantly outdoors or indoors were used to estimate the amount of residents' exposure to mosquito bites in either location, to explore the potential impact a bed net could have had in reducing biting by each vector species. Results: A total of 69,758 host-seeking female mosquitoes comprising 23 species in four genera were collected. The exposure to biting by virtually all vector species was consistently high outdoors, typically at early evening and morning, with exception of An. gambiae s.l which was likely of biting a person with nearly same intensity indoors and outdoors throughout the night. Bed nets use could have reduced biting by An. gambiae s.l (dominated by An. arabiensis), Ma. africana, Ma. uniformis, Cx. pipiens, Cx. antennatus, and Cx. poicilipes by 53%, 47%, 46%, 38%, 31%, and 28% respectively, compared to non-users. Conversely, a bed net user would have had little protection against An. pharoensis, An. ziemanni, An. tenebrosus, and Cx. tritaeniorhynchus biting exposures. Conclusions: This study showed that Massavasse residents were exposed to high levels of outdoor biting by malaria and arbovirus vectors that abound in the village. The findings help to identify entomological drivers of persistent malaria transmission in Mozambique and identify a wide range of arbovirus vectors nocturnally active in rural areas, many with outbreak potential. The study highlights the need for a surveillance system for monitoring arboviral diseases vectors in Mozambique.

Keywords: Malaria; Massavasse village; Mozambique; arboviruses; endophily; exophagy; man-biting exposure; mosquito vectors.

Figure 1.. Map of south Mozambique, showing the location of area studied at Massavasse village in the Lionde administrative post, Chókwè district, Gaza province.

Mozambique administrative border polygons and roads, and the polygons of river lines and water areas were obtained from the Humanitarian Data Exchange ( https://data.humdata.org/). Polygons of cropland areas around Massavasse village were made by authors with Google Earth Pro, using global croplands data obtained from the Global Land Analysis & Discovery ( https://glad.umd.edu/dataset/croplands?s=03).

Figure 2.. Details of the experimental hut used for indoor host-seeking mosquito collections.

Figure 3.. Crude indoor and outdoor hourly (19:00 to 05:00) mean biting density per person/site/night by the predominant mosquito vector species in Massavasse village from February to April 2016.

Biting densities were determined by human landing catches and, are expressed in term of Williams mean (Wm) (see methods).

Figure 4.. Mean hourly adjusted biting exposure in unprotected individuals by dominant mosquito vector species in Massavasse village.

Biting exposure were adjusted by multiplying the crude biting rate by the proportion of people indoor and outdoor at night.