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News / Health / Health Wire

Rare nerve and brain disease spread by mosquitoes confirmed in Tri-Cities area woman

By Annette Cary, Tri-City Herald
Published: November 2, 2023, 7:51am

KENNEWICK — A Franklin County woman has recovered from a rare case of St. Louis encephalitis, a disease transmitted by infected mosquitoes.

She had symptoms and sought medical care last summer, according to the Benton Franklin Health District.

The district said Thursday that testing had recently confirmed that St. Louis encephalitis was the cause of the woman’s illness.

She is believed to have been infected in Franklin County during the summer.

The last time St. Louis encephalitis was detected in Washington state was in 2005, when it was discovered in a flock of chickens that were being maintained by the Benton County Mosquito Control District for West Nile virus surveillance, according to the health district.

The Centers for Disease Control and Prevention said there were 1 to 3 cases in Washington state between 2003 and 2022.

But the Benton Franklin Health District said the last case in Washington from a person infected in the state rather than during traveling was reported in 1972.

The Washington state Department of Health said in an earlier report that several outbreaks of western equine encephalitis and St. Louis encephalitis between 1939 and 1942 in Eastern Washington resulted in numerous cases in people and several deaths.

The Tri-City Herald reported on a 2003 case in a Tri-Cities man that the Department of Health said then was “almost certainly” St. Louis encephalitis caused by a mosquito bite.

The 36-year-old Pasco man told the Herald at the time that a virus had invaded his spine, causing some paralysis, and invaded his brain, leading to inflammation and swelling. He continued to have pain for months.

But the case appears not to have then been positively confirmed as St. Louis encephalitis.

The risk to public health from infected mosquitoes, whether with West Nile virus or St. Louis encephalitis, is currently low, according to the health district.

The recent cold snap has reduced mosquito activity in the Tri-Cities area.

“Although the likelihood of further infections has decreased for the season, it is essential for everyone to remain vigilant and take steps to prevent mosquito bites to reduce the risk of contracting not only SLE (St. Louis encephalitis) but other mosquito-borne diseases,” the district said in a statement Thursday.

St. Louis encephalitis is primarily transmitted through the bite of an infected mosquito. But like West Nile virus, many people infected have no symptoms.

But some people do become ill and may develop encephalitis — inflammation of the brain — or may develop meningitis — inflammation of the membranes that surround the brain and spinal cord, according to the Centers for Disease Control and Prevention.

Precautions are the same as for the prevention of West Nile Virus.

Use insect repellent, wear long-sleeved shirts and pants, and empty standing water.

“In the future, we might see more cases of mosquito-borne diseases in different places due to climate change,” said Erin Hockaday, senior manager of surveillance and investigation for the Tri-Cities based health district. “Diseases carried by insects, like mosquitoes, can become more common and spread to new areas as the climate gets warmer.”