Abstract
Large scale modes of climate variability, including the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), have been shown to significantly impact mosquito-borne diseases in the Tropics, including malaria. However, the mechanistic cascade from ENSO and the IOD, to induced changes in regional climate and ultimately mosquito abundance and behaviour is poorly understood. Mosquito population dynamics, behaviour and their potential to transmit disease are all sensitive to micro-climatic conditions. The warm phase of ENSO (El Niño) tends to be associated with increased precipitation and outbreaks of various vector-borne diseases, while the cold phase (La Niña) can cause drought during the short rains over East Africa. The sensitivity of Anopheles mosquito population dynamics and host-seeking behaviour to ENSO and to the resulting micro-climatic conditions, were investigated in the Kilombero Valley in Tanzania. From June 2016 to September 2017, changes in the timing and intensity of the rainy seasons and temperature due to the ENSO 2016–17 were observed. Mosquitoes were collected using Centres for Disease Control and Prevention (CDC) light traps indoors and mosquito electrocuting traps in- and outdoors. Changes in abundance and biting behaviour of Anopheles arabiensis and Anopheles funestus were correlated with climate and micro-climate. The impacts of El Niño on climate and mosquito abundance were not clear. However, the study area experienced a drought due to La Niña during which both vector species declined significantly. An. arabiensis densities stayed more stable at higher temperatures and were found in higher numbers outdoors with respect to An. funestus. For both species, indoor temperature and season determined their host-seeking location, with higher temperatures and the wet season driving them outside. The study confirmed the influence of ENSO and micro-climate on malaria vector abundance and host-seeking behaviour, generating hypotheses for predicting the impact of future ENSO on malaria risk and vector control. Our observation of higher outdoor biting during warmer conditions indicates that indoor vector control strategies may become proportionally less effective during this time.
Highlights
Despite successful control efforts and a vast reduction in cases and deaths over the last decade, malaria is still a major public health concern in many parts of the world (Bhatt et al 2015a, 2015b, WHO 2018)
Changes in abundance and biting behaviour of Anopheles arabiensis and Anopheles funestus were correlated with climate and microclimate
In most endemic regions of sub-Saharan Africa, mosquitoes of the Anopheles gambiae (An. gambiae s.s. and An. arabiensis its sibling species) and Anopheles funestus complex are the primary vectors for malaria (Collins and Besansky 1994, Donnelly et al 2001, Sinka et al 2012)
Summary
Despite successful control efforts and a vast reduction in cases and deaths over the last decade, malaria is still a major public health concern in many parts of the world (Bhatt et al 2015a, 2015b, WHO 2018). Over 90% of all malaria cases and deaths occur in subSaharan Africa, and malaria continues to be the most significant mosquito-borne disease hampering public health and socio-economic development in this region. Other micro-climatic variables such as temperature have significant impacts on several aspects of adult vector fitness, behaviour and transmission potential (Bayoh and Lindsay 2003, Kulkarni et al 2006). The sporogonic development rate of malaria parasites within vectors increases with temperature, increasing their transmission potential (Shapiro et al 2017). These mosquito demographic and epidemiological parameters determine rates of human exposure to infected mosquito bites
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