First ever human case of mosquito borne Keystone virus identified

Keystone virus, a virus first found in Tampa Bay-area mosquitoes that can cause a rash and mild fever, has been identified in humans for the first time, according to University of Florida researchers.

J. Glenn Morris, director of the UF Emerging Pathogens Institute, and colleagues authored the report published in the journal Clinical Infectious Diseases, whereby they report virus isolation from a Florida teenager with a rash and fever.

Keystone virus, a California-serogroup orthobunyavirus, was first isolated in 1964 from mosquitoes in Keystone, Florida. There are no reports of isolation from humans, despite studies suggesting that ~20% of persons living in the region are seropositive.

The findings are yet another indicator of the range of diseases that can be caused by mosquito bites in Florida, in keeping with a recent study by the U.S. Centers for Disease Control and Prevention that highlighted the almost doubling of vector-borne disease cases in the United States since the early 2000s.

“Although the virus has never previously been found in humans, the infection may actually be fairly common in North Florida,” said Morris.

“It’s one of these instances where if you don’t know to look for something, you don’t find it,” he added.

While there were no reports of human infection until now, human infection has long been suspected. 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.

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

Unexpectedly, UF researchers did find Keystone virus when they did viral cultures from the patient samples. Although the patient did not report symptoms of encephalitis, researchers report that the virus grew well in Neuro-2A cell cultures. Neuro-2A cells are mouse brain cells, and the ability of the virus to grow in these cells suggests that Keystone virus can infect brain cells, and may pose a risk for brain infections.

“This virus is part of a group commonly known as the California serogroup of viruses,” said John Lednicky, Ph.D., a research professor in the UF College of Public Health and Health Professions.

“These viruses are known to cause brain inflammation or encephalitis in several species, including humans,” he added.

Jamestown Canyon virus and La Crosse encephalitis virus are two of the most commonly known viruses in the California serogroup.

Due to the likelihood that Keystone virus is a common though previously unidentified pathogen among people in the region, Morris emphasized the need for additional research into the prevalence of vector-borne diseases in the United States.

“All sorts of viruses are being transmitted by mosquitoes, yet we don’t fully understand the rate of disease transmission,” he 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.’’

Morris also stressed the importance of minimizing the risk of mosquito bites by using mosquito repellent at times and places where mosquitoes are present.

For further reference log on to https://doi.org/10.1093/cid/ciy485