County by county, the West braces for rise in mosquito-borne diseases

As the climate warms, mosquitoes thrive, and communities try to figure out how to prevent disease outbreak.


Sammie Dickson, manager of the Salt Lake City Mosquito Abatement District, is fielding calls lately that go something like this: “My wife and I want to go hiking in Zion National Park. She’s pregnant. Should we worry?”

No, Dickson answers. The mosquito species that carry Zika virus, believed to cause microcephaly in fetuses, aren’t found in Utah.

He knows he probably has only a few more years to say that with certainty, though. As the climate changes, mosquito season is getting longer and a variety of species are thriving in new places in the West. Some types of mosquitoes usually associated with the Southeast where it’s muggy and lush are faring well in drought conditions in California, the Southwest, and some mountain states. Scientists say they’ll breed earlier, survive longer, reach higher altitudes and spread diseases to new regions. And with the multitude of mosquito species and habitats, there’s no silver bullet for stopping them. It will take a combination of things: local governments putting more resources into mosquito control programs, communities educating their residents, and more researchers effectively collecting data. 

Aedes aegypti, the mosquito species known to cause Zika virus, fills up on human blood.

“We need to make sure we have well-funded mosquito programs in areas at risk,” says Joseph Conlon of the American Mosquito Control Association, a nationwide network of entomologists and control experts. Currently, the U.S. has more than 900 mosquito control districts. Each district, funded by local or state governments under varying departments like parks and recreation, health, and transportation, is responsible for monitoring, preventing, and responding to insect-related disease outbreaks in their area.

Funding for mosquito control is closely tied to emerging outbreaks. Since 1999, when West Nile Virus hit the U.S., nearly 42,000 cases of the disease have been reported. The epidemic spread rapidly throughout the West and elsehwere, reaching a peak in 2004. In the years since, federal funding for mosquito control has decreased from $24 million to $10 million, according to a report by the Council of State and Territorial Epidemiologists.

So far, there have been only 153 cases of Zika virus in the U.S., but because of its mysterious link to birth defects, the government is once again mobilizing efforts to combat mosquito-spread disease. President Obama asked Congress for $1.8 billion to fund Zika research and control. Researchers are trying to genetically engineer mosquitoes that die off before they hit adulthood and reproduce. The Environmental Protection Agency and Centers for Disease Control and Prevention are rebooting public health campaigns. Since there’s little data available on mosquito populations nationwide, the CDC recently called for local districts to send in theirs.

Two vectors of Zika virus, Aedes aegypti and Aedes albopictus, have spread to many new regions within the last few years, such as southern Arizona and at least 12 counties in California. These species can also spread Chikungunya virus and dengue fever. Another type of mosquito, the Culex species, is one of the most common mosquitoes in the nation and transmits West Nile Virus. New research shows it may be able to carry Zika as well.

Controlling mosquitoes is a complicated process. It has to be a localized effort, often done with few resources and limited funds, says Heidi Brown, professor of epidemiology at the University of Arizona College of Public Health.

Most of the time, for example, control districts don’t find out communities need mosquito control until there’s already a disease outbreak underway. And outbreaks can have varied intensity, depending on the community. In 2010, UCLA researchers found that low socioeconomic status was an indicator of the likelihood of West Nile Virus cases. The Orange County Mosquito and Vector Control District had the highest rate of West Nile infection and death in the California. Now, the district tries to focus more efforts on poor neighborhoods by cleaning up foreclosed homes and abandoned pools, and educating people about breeding conditions mosquitoes love: overgrown yards and standing water in tires, planters, or even empty cups and bottles.

The tools local mosquito control districts use in reaction to outbreaks aren’t always effective, so an increase in pesticides is almost inevitable as mosquitos expand their range. But there are less toxic options districts can opt for first: mosquito fish can be released to eat larvae in ponds, birdbaths, or ditches. Traps baited with dry ice or bacteria kill adult mosquitoes and their larvae. But as disease paranoia spreads, people are turning to chemical solutions instead. “Humans have an unfortunate habit of thinking that chemicals are the answer, rather than just getting rid of the habitat,” Conlon says.

When government mosquito control districts use chemicals, they’re usually targeting hotspots with EPA-regulated larvicides injected into standing water to kill mosquito eggs or adulticides sprayed from trucks at a hundredth of a pound per acre. Such low doses aren’t harmful, Conlon says. More hazardous by far is the commercial mosquito insecticide market, with unregulated companies claiming they can wipe out mosquito populations by installing misting systems in yards, or by blanket spraying streets and fields with their own cocktail of pesticides.

Pesticides can have many negative effects on humans and the environment: They kill other insect species that benefit habitats, and they are toxic to wildlife and dangerous for humans to breathe. Some cities, like Albuquerque, New Mexico, even allow residents to request a no-spray zone so control districts can’t use pesticides within 1,000 feet of their property.

Recently, the EPA halted production of certain commercial mosquito pesticides because they are unregulated and untested. But that hasn’t stopped people from buying them online and in stores, and it’s led to some ugly battles: In Hotchkiss, Colorado, for example, a man is jail-bound for spraying pesticides on his yard after his wife came down with West Nile. His neighbor, who had cancer and grew organic produce that was pesticide-free, sued for damages, and won. Control experts expect that more of these types of incidents will happen in the future if commercial pesticides aren’t regulated.

As climate change disrupts mosquitos’ normal distribution and disease outbreaks become more unpredictable, more proactive action is necessary. Dickson’s team in Salt Lake City, for instance, created a five-year plan to lessen the risks of mosquito-transmitted disease in the age of climate change by outlining specific tools to use in certain habitats around the city, like wetlands and marshes, urban areas and suburbs. “We’re concerned about a longer season, which means more power, more dollars, and a lot of logistics to make sure we’re doing it [right],” he says. 

Lyndsey Gilpin is an editorial intern at High Country News. She tweets

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