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The Mosquito-Borne Everglades Virus

More than a nuisance, mosquitoes may transmit West Nile and other viruses.

What do mosquitoes, hispid cotton rats, and Burmese pythons have in common? They're all part of an inadvertent experiment in south Florida that could lead to an increase in cases of the Everglades virus.

The Everglades virus is a mosquito-borne disease carried by the hispid cotton rat, which lives in areas with tall grass such as grassy fields, weedy areas, and marshy areas...just the sort of habitats the Everglades provide. In the past, the virus was quite rare in mosquitoes; a 1979 study showed that only 15 percent of the female mosquitoes took their blood meal—necessary for them to reproduce from the hispid cotton rat.

Then the Burmese python arrived. This invasive predator is eating many larger mammals-raccoons, opossums, deer and others—which has caused an increase in contact between the mosquito and the hispid cotton rat. A 2016 study showed mosquitoes now are getting about 77 percent of their blood meals from the hispid cotton rat. That puts south Florida anglers and hunters at increased risk of contracting the Everglades virus, which can cause fever, head-ache, and, rarely, encephalitis.

This is not the only mosquito-borne virus in Florida. The most common are West Nile virus (WNV), eastern equine encephalitis, and St. Louis encephalitis, with a small dash of Zika virus, dengue fever, and chikingunya. Despite all the hoopla about Zika recently, it's not considered a significant problem here; the most important three are WNV, eastern equine encephalitis and St. Louis encephalitis.

The cotton rat, a reservoir for Everglades Virus.

The good news about all these viruses is that they are far less common than the media would sometimes have us believe, even for those of us who spend a lot of time outdoors. For instance, only about 20 percent of people infected with West Nile virus develop symptoms, which include a fever, headache, body aches, swollen lymph glands and a rash. Of people infected, less than 1 percent will develop more severe infections with high fever, neck stiffness, disorientation, coma, seizures, and even paralysis.

Most people who are infected with eastern equine encephalitis show no symptoms, but a few develop mild flu-like symptoms. Rarely, the central nervous system becomes infected, resulting in sudden fever and severe headache, seizures and coma ending in permanent brain damage or death.

St. Louis encephalitis is present in Florida all the time, and a substantial number of people may be infected by it each year but exhibit no symptoms. People who become ill, however, are at risk of long term neurological damage, paralysis, memory loss, and death. It's worth noting that older people are more at risk for disease than children, and that transmission of this particular virus is most likely to take place between August and November, making this one of particular concern for hunters.

Since all these diseases are caused by viruses, antibiotics are not useful against them; that makes the first line of defense, prevention. If you're going to be outside during the early morning or in the evening (and what hunter isn't), use insect repellent and wear a bug suit and headnet to keep mosquitoes away from your skin. If you become ill within two weeks of a hunting trip, be sure you tell your doctor where you were and that you could have been bitten. FS

First published Florida Sportsman December 2017

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