Seasonal variation in abundance and blood meal sources of primary and secondary malaria vectors within Kilombero Valley, Southern Tanzania

Abstract

Background Existing control tools have significantly reduced malaria over the past two decades. However, progress has been stalled due to increased resistance in primary vectors and the increasing role of secondary vectors. This study aimed to investigate the impact of seasonal change on primary and secondary vector abundance and host preference. Understanding the impact of seasonal dynamics of primary and secondary vectors on disease transmission will inform effective strategies for vector management and control. Methods Vector abundance was measured through longitudinal collection of mosquitoes, conducted monthly during the wet and dry seasons, in Sagamaganga, a village in the Kilombero Valley, Tanzania. Mosquitoes were collected indoors using CDC light traps and backpack aspirators, and outdoors using resting buckets baited with cattle urine. In addition, a direct measure of host preference was taken monthly using human- and cattle-baited mosquito electrocuting traps. A host census was conducted to provide an indirect measure of host preference together with monthly blood meal source analysis. All collected mosquitoes were assayed for Plasmodium sporozoites. Results A total of 2828 anophelines were collected, of which 78.5% and 21.4%, were primary and secondary vectors, respectively. The abundance of the primary vectors, Anopheles arabiensis and Anopheles funestus, and of the secondary vectors varied seasonally. Indirect measures of host preference indicated that all vectors varied blood meal choice seasonally, with the direct measure confirming this for An. arabiensis. All anopheline mosquitoes tested negative for sporozoites. Conclusions At the study location, the abundance of both primary and secondary vectors changed seasonally. Indirect and direct measures of host preference demonstrated that An. arabiensis varied from being zoophilic to being more opportunistic during the wet and dry seasons. A similar trend was observed for the other vectors. Graphical Abstract

The role ofAnopheles arabiensisandAnopheles funestusin malaria transmission within houses with different characteristics in South-eastern Tanzania

“…funestus exhibited a strong preference for human blood meals over other potential hosts such as dogs and chickens. This anthropophilic behavior is consistent with the species known tendencies [35]. In recently study conducted in Kilombero valley in 2022, Katusi et al revealed that, An.…”

“…Many houses in the villages prefer to have eave space for air accelerations [42], but in other hands it poses a threat to malaria transmission risks, as mosquitoes are more likely to enter in the house through eave space. Several interventions on house screening have been introduced, this including the idea of eave tube treated with conventional insecticides plus house modification with eave tubes installed with physical barrier inside [42], treated curtains [43] and treated eave ribbons [35, 36], treated chair [46], treated sandals [47], all these tools introduced as structural interventions, in and around the houses, which may impact vector feeding, survivorship, population density and overall vectorial capacity and thus ability to transmit malaria and other pathogens.…”

Rapid assessment of the blood-feeding histories of wild-caught malaria mosquitoes using mid-infrared spectroscopy and machine learning

“…This finding is consistent with previous studies that demonstrated a potential switch in host choice by An. funestus from humans to cattle [ 46 , 47 ]. In brief, given the circumstances of the collections, this observation may be explained by several factors: Firstly, the houses where mosquito collections were conducted had been supplied with intact bed nets before the collections started, which might have created a physical barrier, reducing mosquito exposure to humans [ 48 ]; and forcing mosquitoes to use alternative blood sources in the surrounding areas as previously documented by Iwashita et al [ 48 ].…”

Surveillance and Control of Malaria Vectors in Hainan Province, China from 1950 to 2021: A Retrospective Review

“…Studies in Myanmar in 2019 indicated that An. minimus demonstrated possible resistance to deltamethrin [ 87 ], however, An. dirus in Thailand was shown to be completely susceptible (100% mortality) to transfluthrin [ 88 ].…”