Mosquito-Borne Keystone Virus Has Been Found in Humans for the First Time

But the virus may have been infecting people for much longer than scientists realized

Mosquitoes are vectors for many diseases that infect humans—add one more, Keystone virus, to the list. It's spread by Aedes atlanticus (pictured: the related a. aegypti). USDA ARS

In August 2016, a 16-year-old boy in Florida went to an urgent care clinic with a rash and a mild fever. Florida was in the midst of the Zika outbreak, so doctors collected samples from the teenager to test for the virus. But laboratory tests came up negative for Zika and other related infections, leaving doctors to puzzle over what had made the boy ill.

Dr. Glenn Morris, director of the Emerging Pathogens Institute at the University of Florida, tells Daylina Miller of WUSF News that “it literally took a year and a half of sort of dogged laboratory work to figure out what this virus was.” Now, scientists have revealed the answer to this medical mystery in the journal Clinical Infectious Diseases: The teenager’s symptoms, they report, were caused by Keystone virus, a mosquito-borne infection that has never before been detected in humans.

The Keystone virus is named for the area in Hillsborough County, Florida where it was first discovered in 1964. The virus has been known to infect animals, among them raccoons, squirrels and whitetail deer, that live in coastal regions stretching from Texas to Chesapeake Bay. The Florida teenager’s case marks the first time that Keystone has been found in humans.

Long before 2016, however, there were hints that people had become infected with the virus. A 1972 article in the American Journal of Tropical Medicine and Hygiene reported that Keystone antibodies were found in about one in five people tested in the Tampa Bay area, according to a statement from the University of Florida.

Keystone is thought to be primarily transmitted by the Aedes Atlanticus mosquito, reports Ed Cara of Gizmodo. Keystone belongs to the California-serogroup of viruses, which are known to cause encephalitis, or acute inflammation of the brain, in several species including humans. Fortunately, the first known Keystone patient did not report such severe symptoms. But scientists at the University of Florida found that the virus grew well in mouse brain cells, suggesting that Keystone could pose a risk for brain infections in humans.

In the University of Florida statement, Morris calls for further research into vector-borne diseases like the Keystone virus, which he thinks may have infected many more people than researchers previously realized.

“Although the virus has never previously been found in humans, the infection may actually be fairly common in North Florida,” he said. “It’s one of these instances where if you don’t know to look for something, you don’t find it.”

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