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Thursday, August 23, 2018
New Orleans, LA - A team of U.S. researchers is helping to combat the spread of life-threatening mosquito-borne illnesses by using an unexpected weapon: math.
Tulane University professor Dr. Mac Hyman, an applied mathematician and Past President of the Society for Industrial and Applied Mathematics (SIAM), has created a mathematical model aimed at helping public health workers significantly improve mosquito disease control methods by quashing harmful bacteria in mosquitoes, preventing some diseases from being transmitted altogether.
Mosquitoes are among the deadliest creatures in the world due to the many diseases they can transmit – including the Zika virus, dengue, malaria, West Nile virus, chikungunya, yellow fever and more. According to a recent report from the U.S. Centers for Disease Control and Prevention, diseases transmitted through the bites of ticks, mosquitoes and fleas are a "growing public health problem" in the country. The study shows that reported cases of tick and mosquito-borne diseases more than tripled in the U.S. since 2004.
Current approaches to stop mosquitoes from spreading diseases involve infecting mosquitoes with Wolbachia, a bacteria that blocks viral replication. The idea is to infect them with Wolbachia in the lab and then introduce the mosquitoes into the wild to infect entire mosquito populations. Once infected, mosquitoes are no longer capable of transmitting disease.
According to Hyman, however, using these methods to solve the mosquito problem is not as simple as introducing the virus, which has six different strains. There’s a tipping point that needs to be reached in order for the infestation to be sustained in the wild and that’s where extremely precise math calculations come into play.
“If you release a small amount of infected mosquitoes, it works for a little while, but by Darwinian principles, the infected insects quickly disappear," he explained. “One of the first things we discovered using the mathematical model is that, under ideal conditions, if more than about 30 percent of the mosquitoes are infected with a particular strain of Wolbachia, then the bacteria infection will be sustained.”
To determine the best disease mitigation strategy, Hyman is working with applied mathematician Zhuolin Qu, a post-doctoral fellow at Tulane University, to develop a rigorous mathematical model that simulates what happens in the real world when Wolbachia-infected mosquitoes are released.
Some of the parameters they are investigating to determine the most effective eradication solutions include whether to release males only, females only or both sexes at the same time; whether infected females should be impregnated prior to release; when to spray and/or use a larvicide ahead of a release; where, when and how often to do a release; and which strains of Wolbachia will be most effective for different types of mosquitoes.
In papers published in the SIAM News and SIAM Journal on Applied Mathematics earlier this year, Hyman and Qu demonstrated how their model can be used to calculate the most effective method of introducing a self-sustaining Wolbachia infection. What they found is that the likelihood of sustaining the bacteria in the wild increases if males and pregnant females are released together, and that the area is sprayed first with both insecticide and larvicide to kill adults and eggs.
“This type of mathematical modeling can help identify the best ways to utilize Wolbachia technology to control transmission of Zika, dengue, chikungunya and similar viruses, and eventually suppressing the transmission of these devastating diseases,” said Dawn Wesson, Associate Professor, Tulane University, School of Public Health and Tropical Medicine, and Postdoctoral Fellow of the Malaria Branch of the Centers for Disease Control.
The next step for Hyman and Qu is to extend their models to include spatial variations in mosquito populations. Using data collected from successful field trials recently completed in Australia, where Wolbachia-infected mosquito release are significantly lowering the incidence of dengue fever, they will be examining whether it’s best to release mosquitoes at the edge of the field or in the center, how wind and/or terrain affects the release and other location parameters.
“Almost everything we learn with these types of mathematical models is obvious in hindsight, but we don’t often think about it in foresight,” said Hyman, adding that his team expects to be working with field teams in the coming months.
“Wolbachia is a promising, natural strategy to curb life-threatening disease. Math is helping to make it more effective,” he said.
To view Hyman and Qu’s articles:
Sustained Bacterial Outbreak in Mosquitoes Limits Spread of Life-threatening Diseases
Modeling the Transmission of Wolbachia in Mosquitoes for Controlling Mosquito-Borne Diseases
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Society for Industrial and Applied Mathematics (SIAM), headquartered in Philadelphia, Pennsylvania, is an international society of more than 14,500 individual, academic and corporate members from 85 countries. SIAM helps build cooperation between mathematics and the worlds of science and technology to solve real-world problems through publications, conferences, and communities like chapters, sections and activity groups. Learn more at siam.org.