Do warmer temperatures increase dengue transmission?

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Dengue virus may grow and spread faster at higher temperatures, slowing when the temperature lowers or fluctuates, according to new research. This suggests weather conditions could have an influence on transmission, with upcoming warm periods a warning system for outbreaks.

Many factors have been identified to play a role in dengue fever outbreaks, including human population density and the numbers of mosquitoes in the region. In this study, published recently in Frontiers in Microbiology, the team had noticed that outbreaks in China appeared to be more severe in southern regions. For example, in the 2014 outbreak, Guangdong Province experienced very hot weather, averaging 30°C a day from July to September, and experienced a worse outbreak than neighboring regions, suggesting the temperature might be a factor.

The researchers investigated by infecting mosquitoes with the dengue virus and keeping them in incubators set at temperatures ranging from 18–32°C, in addition, another group was kept in fluctuating temperatures.

The team assessed infection status of the ovaries, midguts and salivary glands of the mosquitoes by polymerase chain reaction at 0, 5, 10, and 15 days post-infection, discovering that in those kept at higher temperatures (23–28°C), there was quicker viral growth and higher viral load. The hot temperatures appeared to lead to a shorter incubation periods and the virus was observed to spread to the mosquitoes’ salivary glands more rapidly.

In lower temperatures the researchers demonstrated that dengue virus grew more slowly, and didn’t spread to salivary glands at all. Moreover, mosquitoes kept at fluctuating temperatures appeared to possess lower levels of virus compared with those kept at a consistently high temperature, suggesting even a temporary drop in temperature may be enough to reduce the chances of mosquitoes becoming infectious.

These findings may help explain the differences in severity observed between different regions during outbreaks. Although further work will be needed to confirm this hypothesis, and assess if it also applies to wild mosquitoes, the results suggest weather patterns could act as a warning system.

Author, Xiao-Guang Chen (Southern Medical University, Guangzhou, China), concluded: “Weather reports should be considered for early warning systems. If the outdoor temperature is high for a sustained period, dengue prevention strategies should be a priority.”

Sources: Liu Z, Zhang Z, Lai Z et al. Temperature Increase Enhances Aedes albopictus Competence to Transmit Dengue Virus. Front. Microbiol. doi:10.3389/fmicb.2017.02337 (2017) (Epub ahead of print); www.eurekalert.org/emb_releases/2017-12/f-mml112717.php

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