Given that the range of the West Nile virus and other mosquito-borne diseases is environmental, changes in the environment mean changes in where these diseases are most likely to spread.
According to a new study published in eLife magazine, the West Nile virus spreads most efficiently in the United States at temperatures between 75.2 and 77 degrees Fahrenheit.
The results suggest that climate change may increase the spread of the West Nile in some places and reduce its spread in others.
“As the climate warms, it’s important to understand how changes in temperature affect the transmission of mosquito-borne diseases,” said lead author Marta Shocket, a postdoctoral fellow at the University of California at Los Angeles.
Shocket and the rest of the study team used models to estimate the impact of temperature on 6 different mosquito-borne viruses, 4 of which are currently found in the United States.
The 6 viruses were:
- Western Nile,
- St. Louis encephalitis,
- Eastern and Western equine encephalitis,
- and Rift Valley fever.
The 6 viruses share some of the same types of mosquito carriers.
The models were based on laboratory experiments that measured how temperatures affect mosquito survival, frequency of biting, mating, developmental factors and the transmission of the virus.
Investigators validated the West Nile model using data on virus transmission in the United States. The West Nile virus is most easily transmitted at certain moderate temperatures, while extreme temperatures limit the survival of relevant mosquito carriers.
“We mainly focus on Culex pipiens, Cx. quinquefasciatus and Cx. Tarsalis, well-studied species that are important vectors for many viruses and for which suitable temperature-dependent data are available for almost all characteristics relevant for transmission, ”the authors of the study write.
“Most of the viruses dealt with in this paper come from temperate areas as tropical diseases that are frequently studied,” said Shocket in a press release. “We compared these results with tropical diseases like malaria and dengue and found that the optimal temperatures and cold thermal limits for viruses to spread are cooler. This means that the viruses spread more efficiently in cooler temperatures than in more tropical diseases, as you would expect. “
While the claims of moderate temperatures may not immediately be a reminder of global warming, the results suggest that mosquito-borne diseases in the US could become a greater burden as global temperatures rise, as the majority of the population (70%) actually lives in places where are currently below the optimal transmission temperature.
Conversely, 30% of the population live in places where summer temperatures are above the optimal temperature, so that transmission there is likely to decrease with global warming.
“Temperature increases could also extend the virus transmission season earlier into spring and later into fall,” the study authors added.
“Climate change stands ready to increase the transmission of West Nile and other mosquito-borne viruses across much of the United States,” said senior author Erin Mordecai, assistant professor of biology at Stanford University. “These diseases also depend on human contact with mosquitoes, which also come into contact with wild animals. Factors such as human land use, mosquito control, the adaptation of mosquitoes and viruses, and the appearance of new viruses predict the future of mosquito-borne viruses Diseases a Challenge. “
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