If you weren't worried about Zika and Lyme disease, here's another mosquito-borne illness to consider, just in time for summer hikes and backyard barbecues.

A teenage boy in Florida has become the first person known to be infected with what is known as the Keystone virus, which is spread by mosquitoes.

The teen went to an urgent care clinic in August 2016 with symptoms including rash and fever. Doctors were concerned he might have an infection caused by the Zika virus but tests came back negative, according to a report on his case published in the journal Clinical Infectious Diseases. Unexpectedly, researchers from the University of Florida (UF) found the Keystone virus when they studied viral cultures from the patient.

The virus was first discovered in the Tampa Bay area in 1964 and was named after the location where it was found. Researchers say it had previously been discovered in animals in coastal area from Texas to the Chesapeake Bay region. Researchers had suspected that the virus could infect people, but this is the first time they found proof.

"Although the virus has never previously been found in humans, the infection may actually be fairly common in North Florida," Dr. J. Glenn Morris, director of the UF Emerging Pathogens Institute and co-author of the report, said in a statement. "It’s one of these instances where if you don’t know to look for something, you don’t find it."

The teenager had relatively mild symptoms, but research suggests the Keystone virus can infect brain cells and may pose a risk for brain infections, similar to encephalitis.

Researchers say the discovery of the Keystone virus in humans shows the importance of more research into the prevalence of mosquito-borne diseases in the U.S.

"All sorts of viruses are being transmitted by mosquitoes, yet we don’t fully understand the rate of disease transmission," Morris said. "Additional 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.’"

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

What is the Keystone virus?
Transmitted by mosquitoes, the Keystone virus has been discovered in humans for the first time.