Study identifies mosquito-borne viruses circulating in Montana
(Missoula Current) Scientists from the National Institutes of Health on Monday said several mosquito-borne viruses are circulating in Montana, which could cause encephalitis and other health effects unfamiliar to most physicians.
According to the findings published in Emerging Infectious Diseases, human infections caused by the viruses may include mild flu-like symptoms or no noticeable illness.
But in some cases, the virus can enter the brain, infect neurons and cause disease resulting in impaired learning and memory difficulties. Paralysis, seizures or death may occur in rare cases.
The study traces its roots back to 2009 when a Montana physician diagnosed a resident with the Jamestown Canyon virus encephalitis after the patient was first misdiagnosed as being infected with the West Nile virus.
“The patient recovered, but the finding prompted the researchers to want to know how prevalent the Jamestown Canyon virus was in the state,” the study said. “If the Jamestown Canyon virus infection was widespread, then regional physicians needed to be aware.”
Scientists from the National Institutes of Health and Rocky Mountain Laboratories in Hamilton collaborated with a retired Missoula neurologist to obtain and test more than 900 random blood samples from six Montana hospitals in different regions of the state.
The researchers tested them for the Jamestown Canyon virus, as well as related viruses like the La Crosse virus, the California encephalitis virus and the Trivittatus virus. The viruses fall under the Orthobunyavirus genus, according to the study.
“Mosquito species that carry those viruses, primarily from the Aedes genus, are found in Montana,” the study stated. “Animals, such as chipmunks, squirrels, rabbits and hares, can be infected with the virus by mosquitoes and act as reservoirs, leading to infection of other mosquitoes.”
According to the findings, between 21% and 40% of the samples collected in Montana tested positive for neutralizing antibodies to at least one of the viruses, meaning the person’s immune system had faced the virus at some point.
The Jamestown Canyon virus was first isolated in Colorado in 1961, and most cases are found in the Midwest. But since 2013, when a new diagnostic test for the virus became available, physicians have diagnosed between 40 and 70 cases in the U.S. each year.
The La Crosse virus was first isolated in the early 1960s in Wisconsin. Since then, encephalitis cases caused by the virus have been found in more than 20 states, mostly in the basins of the Mississippi and Ohio rivers, along with the Appalachian Mountains.
Between 30 and 90 severe hospitalized cases of the virus that affect the central nervous system are reported each year, the study said.