Disease-carrying mosquitoes moving north


Asian tiger mosquito. Image: Center for Invasive Species Research, University of California Riverside

By Eric Freedman

As if climate change-related rising lake levels, extreme weather and threats to biodiversity weren’t enough to worry about, now we can also worry about the public health threat of invading mosquitoes.

That’s a lesson from a new study that warns that higher global temperatures might increase the danger of mosquito-borne diseases to residents of Great Lakes coastal communities.

The boundaries for two mosquito species — already labeled “the costliest invasive species in the world” — are moving northward into the Great Lakes Basin, bringing with them the “ability to transmit diseases of public importance,” including Zika, dengue and yellow fever, according to the study by Environmental Protection Agency scientists.

The cause for concern? The yellow fever mosquito and the Asian tiger mosquito.

“They’re not just coming into new territories. They’re surviving and thriving in those territories,” said Marie Russell, the lead researcher on the project.

The Asian tiger mosquito is moving faster than its fellow invader and has already established itself in Windsor, Ontario, according to Russell, who is based in Chapel Hill, North Carolina..

Study coauthor Joel Hoffman said the two species may compete a little with each other but the yellow fever mosquito is “more concerning for health because it has a strong preference for human hosts” and is the primary transmitter of dengue.

The Asian tiger mosquito, first identified in Wayne County, Michigan, has a broader range of hosts, including dogs and other mammals, said Hoffman, who is based in Duluth, Minnesota.

Michigan State University entomology professor Edward Walker said, “More northern species are retreating to their southern range, and southern species are displacing some northern species.”

North America has about 250 species of mosquitoes, of which about 70 are found in Michigan.

Factors in the territorial shift may include milder winters, according to Walker, a mosquito expert who was not involved in the EPA study.

“Is the winter temperature becoming more tolerable? I think it is,” he said.

Walker also warned that another unwelcome, disease-carrying insect, the lone star tick, has moved northward.

“We now have established populations in Southwest Michigan,” he said. “They have serious implications and add to some of the burdens we already have.”

According to the EPA study, the ranges of both northward-bound species are projected to include the Great Lakes area by 2050, with the Asian tiger extending its range earlier and further.

The study cites a series of adverse impacts due to climate change, including more frequent drought because of decreased snow and ice cover, rising deep water winter temperatures in Lake Michigan and reduced ice cover on Lake Superior. Drought is also associated with epidemics of the West Nile virus.

“In addition, storm surges are likely to become larger, resulting in more microhabitats for mosquito development in cities such as Chicago and Detroit, which are already prone to flooding and standing water,” according to the study in the journal “EcoHealth.”

The Michigan Department of Health and Human Services collects data on viral infections that are spread to people by the bite of infected insects such as mosquitoes and ticks, including data from testing of mosquito pools. The department also offers advice to the public on how to control mosquitoes inside and outside their homes.

Because yellow fever mosquitoes “live near and prefer to feed on people, they are more likely to spread these viruses than other types of mosquitoes,” the U.S. Centers for Disease Control and Prevention says.

Yellow fever mosquito. Image: Centers for Disease Control and Prevention

The “invasive success” of the yellow fever mosquito is primarily due to international trade and travel, the European Centre for Disease Prevention and Control says. It is established in Mediterranean and Caucasus countries and subtropical regions, including the Southeast United States.

The Asian tiger mosquito originated in Southeast Asian tropical forests, has expanded its territory over the past three decades to sections of Europe, Africa, the Middle East and the Americas, and has been identified in at least 32 states.

The EPA’s Russell said how public health agencies address the problem of controlling the invaders is important.

“The response is much better when it’s uniform,” and that includes treating both private and public properties,” she said.

“If you have a scattered or patchy response to mosquitoes, you can see how it could be ineffective. If only a couple of acres are treated, they will move and then return when it wears off.”

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