The Keystone virus is now infecting human beings

Doctors were surprised to find that the samples came back negative for Zika or related viruses. A University of Florida study recently identified the first known human case of the mosquito-borne Keystone virus.

The virus has been known since the 1960's, but for the first time, University of Florida researchers said a human contracted it. The report was published June 9 in the journal Clinical Infectious Diseases.

Unidentified teen went to a walk-in clinic exhibiting a fever and rash. The teenager, a recent transplant to Florida, lacked a natural immunity to Keystone and is reported to be the only one infected at the camp. But the study authors reported that the virus grew well in mouse brain cell cultures, which suggests that Keystone can infect brain cells and may pose a risk for brain infections. They tested for Zika and various other pathogens but hit a series of dead ends.

At present there are no simple diagnostic tests to detect this virus said Dr. Glenn Morris, director of the University of Florida's Emerging Pathogens Institute.

It's part of a group of viruses that are known to cause encephalitis - inflammation of the brain - in several species, including humans. The most common are Jamestown Canyon and La Crosse encephalitis virus.

The virus is carried by a relative of the Aedes aegypti mosquitoes that carry Zika. Like West Nile and Zika, it's spread by mosquitoes.

'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'. Though it was discovered in Florida, the virus has been found in coastal regions as far away as Texas.

Researchers are most concerned by the fact that Keystone virus is part of the "California serogroup" family of viruses, which are known to cause encephalitis, or brain swelling, that can be unsafe.

It's possible that Keystone virus is more widespread amongst people than experts realize, according to the case report.

"Morris said in a statement: "All types of viruses are being transmitted by mosquitoes, yet we don't fully understand the rate of disease transmission", in research into the spread of vector-borne diseases will help us shine a light on the pathogens that are of greatest concern to both human and animal health".

The virus has been found in animals such as deer and squirrels, but researchers had never seen it in a human before.

Plus, they wrote, this finding underscores the fact that there are all kinds of diseases circulating out there that could one day infect humans.