AsianScientist (Dec. 6, 2017) – Scientists in China have discovered that higher temperatures accelerate the rate of dengue virus maturation and worsens its spread among mosquito populations. They published their finding in Frontiers in Microbiology.
An estimated 390 million people are infected each year with the dengue virus, which can cause serious symptoms such as hemorrhagic fever and dengue shock syndrome. The virus is transmitted to humans through mosquito bites. It replicates during an initial incubation period beginning in the mosquito’s gut, before spreading to reach its salivary glands. While feeding, the mosquito transmits the virus in its saliva.
Many different factors can play a role in dengue fever outbreaks, including human population density and the numbers of mosquitoes in the region. In China, outbreaks tend to be worse in southern regions, such as Guangdong Province. In one such outbreak in 2014, a massive 96 percent of cases were concentrated in Guangzhou.
In this study, the researchers infected mosquitoes with dengue virus and kept them in the lab in incubators set at 18°C, 23°C, 28°C or 32°C. Another group of mosquitoes experienced temperatures that fluctuated each day (28°C for 14 hours, 23°C for 2 hours and 18°C for 8 hours). The researchers then determined how much the virus had replicated and whether it had spread throughout the mosquitoes’ bodies.
The research team found that higher temperatures (23-28°C) resulted in more rapid viral growth and higher levels of virus. The hot conditions also led to a shorter viral incubation period, and the virus spreading to the mosquitoes’ salivary glands much earlier.
Under the coolest conditions, at 18°C, the virus grew very slowly and did not spread to the salivary glands at all, reducing the chance that the mosquitoes could transmit it to humans. This might explain why cooler regions suffer less from dengue fever.
Interestingly, under fluctuating temperatures, the mosquitoes also showed lower levels of virus in their salivary glands compared with those kept at a constant 28°C. This suggests that even a temporary drop in temperature might be enough to reduce the infectiousness of mosquitoes.
The scientists intend to carry out further work to see whether this hypothesis is correct, and whether their results are applicable to mosquitoes in the wild.
“Weather reports should be considered for early warning systems,” said study author Dr. Chen Xiao-Guang of the Southern Medical University in Guangzhou. “If the outdoor temperature is high for a sustained period, dengue prevention strategies should be a priority.”
The article can be found at: Liu et al. (2017) Temperature Increase Enhances Aedes albopictus Competence to Transmit Dengue Virus.
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Source: Frontiers; Photo: Shutterstock.
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