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Dengue In The Time Of COVID: Keys Fighting On Two Viral Fronts

A Florida Keys Mosquito Control District staffer refills a helicopter with liquid larvicide while it is on the ground at Key Largo School.
Chad Huff
Florida Keys Mosquito Control District
A Florida Keys Mosquito Control District staffer refills a helicopter with liquid larvicide while it is on the ground at Key Largo School.

In the Florida Keys, health officials are fighting to stop the spread of COVID-19. But they've also got another fight on their hands. For the second time in a little more than a decade, there's an outbreak of dengue fever on the island chain.

The Keys are known to be home to Aedes aegypti, the mosquito that can transmit dengue — along with other diseases like Zika — to humans.

"Unfortunately we have the perfect storm," said Andrea Leal, executive director of the Florida Keys Mosquito Control District. "In 2019, we saw more imported cases of dengue fever in the state of Florida than we've seen, ever. And so we're all on guard … it's just a matter of time before we start seeing locally-acquired cases."

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The local office of the state Department of Health learned about the first case in Key Largo in early March.

"We responded to that case in March and then didn't hear another thing until June so we had our fingers crossed, thinking 'OK, we did this, we have it under control,'" Leal said. "But unfortunately, come early June, it was another story."

So far, more than 50 cases of dengue have been identified in Key Largo this year — some of them through antibody tests that showed people had contracted the disease months earlier. During the 2009-2010 outbreak in Key West, 88 people were diagnosed with locally acquired dengue.

An Aedes aegypti mosquito
James Gathany
Female Aedes aegypti mosquitoes can transmit diseases like dengue fever and Zika by biting infected people, then biting someone else.

The Mosquito Control District works with the Department of Health to target areas where the disease has been found.

"They let us know as soon as there's a suspect case so we're not waiting a week or two for confirmation. As soon as someone is being tested for dengue, they let us know, they give us the area the person lives in or any of the areas they may have been exposed to mosquitoes that they remember. And we send our teams into that area immediately," Leal said.

"Basically we're going through everyone's yards. We're dumping any standing water, treating any water that we can't dump, educating residents on mosquito control," she said. "We'll do handheld adulticide treatment if there are any mosquitoes that we find in the area, setting a number of adult traps just to know what's going on with the population."

She said most people are cooperative about letting the inspectors onto their property, even during the COVID-19 pandemic.

"Our inspectors are wearing masks and gloves as they're going through everyone's property. They're changing out gloves from house to house so anything that we're touching we're making sure that we're taking the correct precautions to protect not only our employees, but the public," she said.

The district is also using helicopters to spray liquid larvicide and fog trucks to spray malathion, because they are seeing mosquitoes becoming resistant to pyrethroids, Leal said.

The number of female Aedes aegypti mosquitoes found in traps in the area has been substantially reduced, she said.

Dengue fever is rarely fatal. But you want to avoid it if at all possible, said Bob Eadie, Monroe County administrator for the Department of Health.

"It's a really debilitating disease. It's called break bone fever and that's the reason — you feel so absolutely miserable," he said.

Dengue is not directly contagious from person-to-person, like COVID-19. But the Department of Health still does a sort of contact tracing once someone is diagnosed.

"The way the disease is transmitted is an infected person has to be bitten by an aegypti mosquito. That mosquito has to then, within a certain time frame, bite someone else," he said.

The real key to stopping the disease is eliminating standing water. Eadie said Aedes aegytpi has evolved to survive around people.

"It's called a house mosquito. It can breed in a capful of water," he said. "I'm talking about a bottle cap."

Combating 'disease fatigue'

Eadie said it's a challenge to deal with a pandemic and a local outbreak of mosquito-borne disease at the same time.

"We may have a really good team but we don't have a very strong bench is what happens. We wear people out," he said. "Also, I think people may be having some disease fatigue in some ways in the sense that if you have the disease and you recover from one or the other you really don't want to be bothered by talking about it any more and you're OK so you're just not going to worry about it."

Leal said the pandemic has both helped and hurt the response to the dengue outbreak.

"COVID has really kept people in place. So you don't have people moving around as much, which I think is why we saw such heavy numbers in isolated areas in Key Largo. You're not visiting your friends or going to parties like you used to and remember with dengue, it's the people that really are the ones that are moving the disease around," she said.

"But on the other side, we're all stuck at home, so we're outside more. And that's one of the things that we saw going through those neighborhoods is that people are taking two or three walks a day and they're outside more often than what they would have been on normal occasions."

Besides eliminating standing water, other ways to prevent mosquito bites are keeping screens in good shape, wearing mosquito repellent, and wearing long pants and long sleeves when you're outside.

Nancy Klingener was WLRN's Florida Keys reporter until July 2022.
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