A mosquito-borne illness originally found in the Tampa Bay area has been confirmed in a human for the first time, according to University of Florida researchers.

The Keystone virus, named after the northwestern Hillsborough County area where it was initially identified in 1964, has been found in animal populations along coastal regions stretching from Texas to the Chesapeake Bay.

UF researchers have been sequencing the virus since August 2016, when a 16-year-old boy in North Central Florida showed up to a clinic with a rash and fever during the Zika virus epidemic in Florida and the Caribbean. The report was published June 9 in the journal Clinical Infectious Diseases.

Because of concerns about Zika, laboratory samples were collected from the patient, but studies were negative for Zika or related viruses.

But the researchers found Keystone virus when they did viral cultures from the patient samples. Although the teenager did not report symptoms of encephalitis, lab studies indicate that Keystone virus can infect brain cells, and may pose a risk for brain infections.

Dr. Glenn Morris, director of the university's Emerging Pathogens Institute, said until now, there hasn't been a way to test for the virus.

"We couldn't identify what was going on,” Morris said. “We screened this with all the standard approaches and it literally took a year and a half of sort of dogged laboratory work to figure out what this virus was.”

Morris said biotech companies are already reaching out to the institute to develop commercial tests that can be used in clinics and hospitals.

Keystone is spread by aedes atlanticus, a common Florida mosquito and cousin to the mosquito, aedes aegypti, that spreads Zika.

It’s part of a group of viruses that are known to cause encephalitis - inflammation of the brain - in several species, including humans. Morris said they’re not absolutely certain that Keystone can also cause encephalitis.

Morris said although the virus has never previously been found in humans, the infection may actually be fairly common in North Florida. A 1972 article in the American Journal of Tropical Medicine and Hygiene reported Keystone virus antibodies in 19 to 21 percent of the people tested in the Tampa Bay region.

“There’s a high likelihood that Keystone virus is continuing to circulate in Florida, as it has for at least 50 or 60 years, and as it may well have for hundreds of years,” Morrisa said. “This is one of our native Florida viruses.”

"It's likely there have continued to be a fair number of human infections. In most instances, it would appear to be asymptomatic or cause mild infection, fever and a rash."

Morris emphasized the need for additional research into the prevalence of vector-borne diseases in the United States, and stressed the importance of minimizing the risk of mosquito bites by using mosquito repellent.