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The First Human Case Of The Mosquito-Borne Keystone Virus Has Been Reported In Florida

The virus, which normally infects animals, was discovered in Florida 50 years ago. This is the first time it has been isolated from a human.

Posted on June 22, 2018, at 4:57 p.m. ET

The first human case of Keystone virus, a mosquito-borne infection, was identified in a 16-year-old boy in Florida.

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Grab your bug spray because researchers have just discovered yet another mosquito-borne germ that can infect humans, joining the ranks of viruses like Zika, West Nile, and chikungunya.

Researchers from the University of Florida isolated the Keystone virus from a human for the first time after testing a 16-year-old boy who had a rash and fever, according to a study published in the journal Clinical Infectious Diseases. However, there is some evidence that the virus may have been infecting Floridians for years without anyone realizing it.

The Keystone virus belongs to a wide group of viruses called bunyaviruses

specifically, the California serogroup — which infect animals throughout the US and occasionally, humans. "We actually know very little about these viruses other than some of them are known to cause severe but rare infections in humans," John Lednicky told BuzzFeed News. Lednicky is the author of the study and a research professor in the department of environmental and global health at the University of Florida in Gainesville.

Other viruses in this group include the La Crosse encephalitis virus and California encephalitis virus, which can cause inflammation of the brain that can be potentially life-threatening — although most people have no apparent symptoms. Fortunately, the boy infected with Keystone virus recovered from the infection.

The virus was first discovered in 1964 among mosquitos in the Tampa area and has been found in animals around the Southeastern US.

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It's named after the Keystone region of Florida, where it was first identified some 50 years ago. The germ is spread by the Aedes atlanticus, which is one of the most prevalent mosquitoes in Florida, said Lednicky.

Keystone virus is typically found in white-tailed deer, squirrels, and raccoons in the southeast, stretching from Maryland to Texas. It has never been isolated from a human, until now.

However, previous studies have suggested that the virus has been infecting people in Florida for years. "They did antibody tests in people living in the Tampa area [after Keystone was discovered] and about 20% of people seemed to have antibodies against the virus," he said.

Tests for antibodies, which are immune system proteins, are an indirect way of testing for a virus, so it is not 100% certain that these people actually had Keystone. "There are many bunyaviruses so just because you have antibodies that react with Keystone that doesn't mean it's keystone, you may have been infected with a closely related virus," Lednicky said.

The teen developed symptoms in August 2016 after attending a band camp in North Florida. It took over a year to confirm the diagnosis of Keystone virus.

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The 16-year-old had been attending a marching band camp where he practiced outside until the evening hours — prime feeding time for mosquitoes. "He had a rash that started on his abdomen and spread throughout the rest of his body and the day before he complained about being very hot and having muscle aches and ankle pain," Lednicky said.

The boy visited an urgent care clinic in August 2016, where doctors initially thought the rash was an allergic reaction. They also tested the boy for Zika, which was causing an epidemic at the time in Latin America and the Caribbean, but it came back negative.

After another year of additional testing, doctors finally found the unlikely culprit: Keystone virus. "Like many mosquito-borne diseases, you get a rash, slight fever, and muscle aches — but so many other viruses cause the same symptoms," said Lednicky. So it isn't always easy to diagnose these infections.

"One big point is that this kid had recently moved to Florida, so maybe only he developed a rash because most Floridians have already been exposed to the virus," said Lednicky. More research needs to be done to understand the Keystone virus, its prevalence, and the rate of transmission.

There's no need to panic, but it's always a good idea to avoid mosquitoes because they can spread a number of other viruses and parasites.

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The good news is that there's no active outbreak of Keystone, and it's possible that the virus has made people sick before but only caused mild symptoms or none at all. "If the old reports are correct, then a lot of people have been exposed to this virus and didn't even know it," Lednicky said.

However, it's important to be aware of mosquito-borne illnesses in the US because in rare cases, they can result in serious illness or death. If you have any questions or you think you have a virus or parasite from a mosquito bite, talk to a health care provider.

One of the best things you can do to reduce your risk is to take steps to prevent mosquito bites. The Centers for Disease Control and Prevention recommends wearing insect repellent (preferably containing DEET) and covering up exposed skin with long sleeves and pants when you are outside, and using screens or nets to keep mosquitoes out of your home.

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