Global spatial assessment of Aedes aegypti and Culex quinquefasciatus: a scenario of Zika virus exposure

Abstract

Zika virus (ZIKV) is an arbovirus transmitted mainly by Aedes aegypti mosquitoes. Recent scientific evidence on Culex quinquefasciatus has suggested its potential as a vector for ZIKV, which may change the current risk zones. We aimed to quantify the world population potentially exposed to ZIKV in a spatially explicit way, considering the primary vector (A. aegypti) and the potential vector (C. quinquefasciatus). Our model combined species distribution modelling of mosquito species with spatially explicit human population data to estimate ZIKV exposure risk. We estimated the potential global distribution of C. quinquefasciatus and estimated its potential interaction zones with A. aegypti. Then we evaluated the risk zones for ZIKV considering both vectors. Finally, we quantified and compared the people under risk associated with each vector by risk level, country and continent. We found that C. quinquefasciatus had a more temperate distribution until 42° in both hemispheres, while the risk involving A. aegypti is concentrated mainly in tropical latitudes until 35° in both hemispheres. Globally, 4.2 billion people are under risk associated with ZIKV. Around 2.6 billon people are under very high risk associated with C. quinquefasciatus and 1 billion people associated with A. aegypti. Several countries could be exposed to ZIKV, which emphasises the need to clarify the competence of C. quinquefasciatus as a potential vector as soon as possible. The models presented here represent a tool for risk management, public health planning, mosquito control and preventive actions, especially to focus efforts on the most affected areas.

Keywords: Arbovirus; ZIKV risk; exposure level; mosquito; spatial epidemiology.

Fig. 1.

(a) Suitability map of Culex quinquefasciatus worldwide. The colours represent the suitability level from 0 (blue) to 1 (red). (b) Potential interaction zones between Culex quinquefasciatus and Aedes aegypti worldwide, categorised by levels of interaction.

Fig. 2.

Transmission risk model of ZIKV due to the vector Culex quinquefasciatus. (a) Map of the transmission risk of ZIKV worldwide by C. quinquefasciatus. (b) Zoom to the transmission risk map of America. (c) Zoom to the transmission risk map of Africa. (d) Zoom to the areas with higher transmission risk in Oceania. (e) Zoom to the transmission risk map of Europe.

Fig. 3.

Transmission risk model of ZIKV due to the vector Aedes aegypti. (a) Map of the transmission risk of ZIKV worldwide by A. aegypti. (b) Zoom to the transmission risk map of America. (c) Zoom to the transmission risk map of Africa. (d) Zoom to the areas with higher transmission risk in Oceania. (e) Zoom to the transmission risk map of Europe.

Fig. 4.

Combined risk map of A. aegypti and C. quinquefasciatus worldwide. (a) Map of the potential transmission risk of ZIKV worldwide. (b) Zoom to America. (c) Zoom to Africa. (d) Zoom to Oceania. (e) Zoom to Europe.

Fig. 5.

Differential in the percentage of people exposed to ZIKV by the two vectors, showing which of the vectors accounts for the difference, by continent and by risk level.

Fig. 6.

Spatially explicit differential in the percentage of people exposed to ZIKV by both vectors, showing which of the vectors accounts for the difference, by country. In grey, if the studied vectors are not present according to the models; in white, if there is no difference in the percentage of population exposed between both vectors; in purple, if Aedes aegypti accounts for the difference; in yellow if Culex quinquefasciatus accounts for the difference. The darker colour of each palette indicates that only that vector species is present in the country according to the model.