Impact of recent climate extremes on mosquito-borne disease transmission in Kenya.

Cameron Nosrat,Francis Mutuku,Assaf Anyamba,A Desiree Labeaud,Bryson Ndenga,Jamie M Caldwell,Richard Damoah,Jonathan Altamirano,Elvina Viennet

doi:10.1371/journal.pntd.0009182

Abstract

Climate change and variability influence temperature and rainfall, which impact vector abundance and the dynamics of vector-borne disease transmission. Climate change is projected to increase the frequency and intensity of extreme climate events. Mosquito-borne diseases, such as dengue fever, are primarily transmitted by Aedes aegypti mosquitoes. Freshwater availability and temperature affect dengue vector populations via a variety of biological processes and thus influence the ability of mosquitoes to effectively transmit disease. However, the effect of droughts, floods, heat waves, and cold waves is not well understood. Using vector, climate, and dengue disease data collected between 2013 and 2019 in Kenya, this retrospective cohort study aims to elucidate the impact of extreme rainfall and temperature on mosquito abundance and the risk of arboviral infections. To define extreme periods of rainfall and land surface temperature (LST), we calculated monthly anomalies as deviations from long-term means (1983-2019 for rainfall, 2000-2019 for LST) across four study locations in Kenya. We classified extreme climate events as the upper and lower 10% of these calculated LST or rainfall deviations. Monthly Ae. aegypti abundance was recorded in Kenya using four trapping methods. Blood samples were also collected from children with febrile illness presenting to four field sites and tested for dengue virus using an IgG enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). We found that mosquito eggs and adults were significantly more abundant one month following an abnormally wet month. The relationship between mosquito abundance and dengue risk follows a non-linear association. Our findings suggest that early warnings and targeted interventions during periods of abnormal rainfall and temperature, especially flooding, can potentially contribute to reductions in risk of viral transmission.

Highlights

Climate change’s influence on temperature and rainfall can dramatically impact vector abundance and the dynamics of vector-borne disease transmission
As climate change leads to extremes in rainfall and temperature, the abundance and populations of these vectors will be affected, influencing transmission of dengue
Our results contributed to a better understanding of the effect of climate variability and change on dengue

Summary

Introduction

Climate change’s influence on temperature and rainfall can dramatically impact vector abundance and the dynamics of vector-borne disease transmission. Scientific evidence suggests that as global climate change continues to intensify, so will the frequency of extreme climate events, including floods, drought, heat waves, and cold waves [1,2,3,4]. Extreme climate events result from both natural internal climate variability and climate warming [5]. Water availability during extreme climate events, including droughts and floods, can have important implications for mosquitoborne disease transmission, as pools of water provide breeding sites for infectious disease vectors. Transmission of dengue fever, a prevalent arthropod-borne disease in Kenya that is the focus of this study, can be affected by variability in temperature and rainfall [6, 7]

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Conclusion