Abstract
Vector-borne diseases account for more than 17% of all human infectious diseases and result in more than 700,000 deaths annually. A significant part of vector-borne diseases is caused by pathogens transmitted by mosquitoes, and include diseases as relevant as Malaria, Dengue, or West Nile Fever.
Mosquitoes are ectotherms; therefore, their physiology and life histories are driven by environmental temperature (Mordecai et al., 2013). Similarly, the processes involved in the transmission of mosquito-borne pathogens are highly dependent on ambient temperatures (Shocket et al., 2018). The relationship between those factors and the temperature is usually unimodal (i.e., once the minimum temperature needed for that factor is reached, the value of the factor increases until it peaks at an optimum temperature, and then decreases to zero at the maximum temperature). The transmission of mosquito-borne diseases can be quantified using the Basic Reproductive Number (R0), which defines the number of cases of a disease that arise when one case is introduced into a totally susceptible population. An ideal approach to evaluate the relationship between the risk of transmission of mosquito-borne diseases and temperature is the R0 equation.
The objective of our study was to quantify the effect that the precision with which temperature is measured (hours, days, months) has on the estimates of transmission of mosquito-borne diseases. In order to do that, we used mechanistic models to quantify the basic reproductive number (R0), which we applied to different mosquito-pathogen combinations: West Nile virus (WNV) and Culex pipiens, dengue virus (DENV) and both Aedes albopictus and Aedes aegypti and P. falciparum malaria parasites and Anopheles mosquitoes. At the world level, the higher the precision, resulted in significantly smaller estimates of transmission and much larger transmission areas, and those results were consistent for different mosquito-pathogen combinations and for the different months of the year. However, when that effect was evaluated at a smaller spatial scale (i.e. climatic areas), spatio-temporal heterogeneities were observed. For example, hourly rather than monthly temperatures tended to decrease the estimates of transmission in areas of tropical climate but increased them in areas of continental climate. While those effects were clearly different between climatic areas, they were consistent for the different mosquito-pathogen combinations within a climatic area.
References
Mordecai, E. A., Paaijmans, K. P., Johnson, L. R., Balzer, C., Ben‐Horin, T., de Moor, E., ... & Lafferty, K. D. (2013). Optimal temperature for malaria transmission is dramatically lower than previously predicted. Ecology letters, 16(1), 22-30.
Shocket, M. S., Verwillow, A. B., Numazu, M. G., Slamani, H., Cohen, J. M., El Moustaid, F., ... & Mordecai, E. A. (2020). Transmission of West Nile and five other temperate mosquito-borne viruses peaks at temperatures between 23° C and 26° C. Elife, 9, e58511.