According to new research from Georgia State University, the timing of hurricanes is one of the primary factors influencing its impact on the spread of mosquito-borne diseases such as West Nile Virus, dengue, chikungunya, and Zika.

Researchers from Georgia State, and their colleagues at Arizona State University, developed a mathematical model to study the impact of heavy-rainfall events like hurricanes on the transmission of mosquito-borne diseases in temperate areas of the world. This includes the southern coastal United States, where most hurricanes land.

In the aftermath of a heavy-rainfall event, the mosquito population often booms as a result of many areas of stagnant water forming perfect environments in which the insects can lay their eggs. At the same time, the private and public health infrastructure can break down, leaving diseases unchecked and able to spread. And the risk of disease outbreaks is highest if the hurricane happens early in the “transmission season,” or the period of time where mosquitoes are able to pass the virus on to humans.

According to the study, a hurricane that occurs on June 1 results in 70 percent more disease cases than a hurricane that occurs on July 1.

“Mosquitoes are very sensitive to temperature, not only in terms of their ability to survive and reproduce, but also in their ability to infect individuals,” said Georgia State’s Gerardo Chowell, lead author of the study. “The warmer it is, the faster an infected mosquito will be able to transmit the virus. Considering that mosquitoes have an average lifespan of less than two weeks, that temperature difference can have a dramatic effect on disease outbreaks.”

Population displacement can also affect the spread of mosquito-borne diseases in several ways. When people leave the local area, it reduces the number of infections in that area but potentially increases the number of infections elsewhere. People who stay in the area tend to be at higher risk due to pools of standing, stagnant water. And even disaster or emergency relief workers can transmit the diseases when they return to their homes.

“Since mosquito-borne diseases tend to be spread by the movement of people rather than the movement of mosquitoes, disaster-induced movements of people can shift where and when outbreaks occur,” said Charles Perrings of Arizona State, a co-author of the study.

Considering that climate change is causing increasingly frequent high-rainfall events and hurricanes in the southern U.S. and other tropical areas, mosquito-borne diseases are only going to become more common. This means that researchers need to develop tools to assess how these disasters can affect the risk of disease transmission.

Photo: Hurricane Maria makes landfall on Puerto Rico. Credit: Shutterstock