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You probably know by now that the Aedes aegypti mosquito is the species that takes the majority of the blame for the transmission of Zika. This mosquito thrives in warm, coastal regions, which means that it is most common in the tropics (namely Latin and South America), but it can also survive in the southern United States. Given these geographical parameters, there hasn’t been a great deal of concern about the mosquito’s ability to spread Zika in northern regions, including our area.

However, research has revealed that there is an isolated population of Aedes aegypti mosquitoes that has found a new home in DC, just a few blocks away from the US Capitol building. This information was published in a paper in the American Journal of Tropical Medicine and Hygeine last year. The Capitol Hill group of mosquitoes appears to be the only documented population found north of the mosquito’s typical range thus far.

Right now, the mosquitoes in DC are not carrying Zika, but there is a small risk of human transmission in the future. A recent Washingtonian article explains how the population was discovered and how it is being handled.

“It’s a small population, so the chances of human transmission are modest. But, for me, as an entomologist, it’s like a little red flag.” said Dave Severson, a medical entomologist with the University of Notre Dame, who has worked with the species most of his career. “It’s unprecedented for this mosquito to be breeding in this climate.”

Finding the DC population was something of a fluke. In late October, 2011, a mosquito expert named Andrew Lima got a call from a friend who lives a few blocks east of the Library of Congress. The friend noticed mosquitos in his basement apartment — mosquitos that seemed unusually robust for that time of year. Knowing that Lima might be interested in seeing the bug, he called him over.

“I went into his place,” Lima recalled. “I saw it within a minute of being in there. I saw it fly up from a low level, and I did a cup swat— a gentle stunning of the mosquito—so I could see what type it was, and it was a clean enough kill that I could tell it appeared to be Aedes aegypti.”

Lima then wandered around the townhouse, taking a sample of water from a stagnant fountain. A few days later, he came back to the neighborhood and took samples from a bird bath, trash can, and plant saucer, all within about 100 meters of the house. “I kind of thought that’d be it,” Lima said.

But the following year, in September, he went back to the same bird bath, where he found more Aedes aegypti larvae. He then contacted Severson—the preeminent expert on Aedes aegypti—and sent samples to his lab for testing, to see if the samples Lima had collected in 2011 were genetically linked to the 2012 samples. In other words, Lima wanted to know if the first batch had survived the winter, or if the second batch was a “new introduction” that just happened to show up that summer.

In 2013 and 2014, Lima collected yet more samples from the same area, sending them to Severson’s lab, where testing found a genetic link between each year’s samples—meaning the mosquitos were surviving the winter. They had made Capitol Hill their home.

“That’s when we came to the conclusion there must be some underground sites in the area where you have this continuous production,” Lima recalled. “The more I walk around there, the more I see exactly the kind of situations that look like there could be protected places where they could be surviving. There are Metro stations, there are the tunnels under the Capitol.”

Of course, there are tunnels and underground pockets in lots of cities. But Lima has a hypothesis: With so many diplomats and so many expats in DC, Aedes aegypti had a higher chance of hitching a ride from its natural environments back to the District.

“I’m thinking someone brought some favorite article or vase from their native country, and set it out in their yard,” he said. “It filled up with water, and those eggs were activated by the water and hatched here.”

Whatever route they took to DC, they appear to be here to stay. By the time their journal paper had been reviewed and edited, Severson and Lima confirmed that the mosquitoes survived another winter–the fifth in a row.

Lima says the city’s Department of Health is aware of their paper, but isn’t taking any precautions or steps that he knows about. The city’s website has a page on Zika, with warnings, statistics and advice for protecting against mosquitoes, but does not mention a resident Aedes aegypti population.

The department did not immediately respond to a request for an interview. Severson says public health departments should be taking Lima’s discovery very seriously.

The news that Zika mosquitoes have been discovered so close to home is certainly worrisome, but there are precautions we can take to try to stop the virus from becoming an outbreak in the DC area. It’s especially important to protect yourself from bites and to remove standing water on your property. You can always refer to our 5 T’s of mosquito control, and check the CDC’s guidelines for more information.

Contact DC Mosquito Squad if you’d like to explore treatment programs that can help eliminate mosquito populations in your yard.

Read our other blog articles related to Zika:

7 Facts About The Zika Virus
As the Zika Virus Spreads, Here’s What You Need To Know
Which Mosquito Spreads Zika?
Zika and Guillain Barre in Colombia
Why is the Zika Epidemic Happening Now?
A New & More Common Mosquito Can Spread Zika Virus
Zika Neuro Disease Link for Adults