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Though Zika and West Nile viruses get more publicity, La Crosse encephalitis is the state’s and the country’s most common cause of mosquito-borne illness.

East Tennessee Children’s Hospital is reporting a spike in children diagnosed with a mosquito-borne virus that, left undetected, can cause brain damage or, rarely, death.

Dr. Lori Patterson, infectious disease physician at the hospital, said doctors there have seen seven children in four weeks with La Crosse encephalitis.

Typically, Tennessee sees a dozen cases of the virus in a year.

Though Zika and West Nile viruses get more publicity, La Crosse encephalitis is the state’s and the country’s most common cause of mosquito-borne illness. The virus, which occurs more frequently in children 16 and younger, irritates the brain; symptoms can include headache, fever, nausea, vomiting, drowsiness and dizziness, and in severe cases, seizures or coma. There’s no vaccine or specific treatment for the virus itself; supportive care — treating symptoms — usually requires hospitalization.

La Crosse encephalitis is diagnosed by blood test and reportable to the state health department and the federal government. Patterson said Tuesday that the seven hospital patients’ diagnoses were confirmed. The state department of health hasn’t provided a statewide number of cases for this year, though East Tennessee typically sees far more cases than the rest of the state. All three of last year’s confirmed cases were in this region — one each in Jefferson, Sevier and Hamblen counties.

And East Tennessee and Appalachia are hotbeds for the virus, accounting for more than a quarter of cases nationally. Between 2004 and 2013, only North Carolina, Ohio and West Virginia had more cases than Tennessee’s 105, all but a few in the eastern part of the state. Most states reported no cases.

In addition to the Eastern treehole mosquito, which can breed in as little as a tablespoon of water, the Asian tiger and Asian bush mosquitoes also carry La Crosse encephalitis, researchers at the University of Tennessee and in North Carolina confirmed in 2001.

Not only are those two non-native species of mosquito prevalent in this area now, they’re aggressive biters, said Dr. Rebecca Trout Fryxell, an entomologist and assistant professor at the University of Tennessee Institute of Agriculture. And all three species bite during the day.

Since the 2012 death of a Union County boy from the virus, Fryxell has devoted her professional work to figuring out how to disrupt the breeding and biting patterns of the mosquitoes that carry La Crosse encephalitis. She said the hospital’s diagnoses line up with the increasing number of potentially infected mosquitoes she and her students have found this season in Anderson, Hamblen, Washington, Carter and Sullivan counties.

Between May and the end of July, the average number of mosquitoes found in each of the researchers’ 75 traps has increased. The number of Asian tiger mosquitoes was the highest, averaging five per trap on July 26, she said. Last week one of her students began trapping at 35 Knox County sites.

“Last year our mosquito populations were increasing in abundance until the drought occurred in mid-July,” Fryxell said. “This year, we have yet to see the mosquito populations ‘peak’ ” and start to decline — they’ve continued to increase overall and at each trap site, she said.

Knox County sprays for the Culex mosquito, which carries West Nile virus, in neighborhoods where trapped mosquitoes test positive for West Nile — usually a handful a year.

But the chemicals used — a mixture of synthetic permethrin and piperonyl butoxide — don’t affect the Eastern treehole mosquito, which likes wooded areas and lays eggs in tiny hollows, or the non-native species. And while the Culex mosquito is more active at night, atmospheric conditions make spraying ineffective during daylight hours, when the Asian tiger and Asian bush mosquitoes are biting.

What can make a difference is applying a repellent containing the chemical compound DEET, or oil of lemon eucalyptus, and dressing children in long sleeves and long pants when possible, health officials said. Keeping grass and shrubbery short, ridding your property of dead trees, filling in hollow stumps with sand or concrete, and dumping standing water around your property — even the little bit that collects under flowerpots or on trash-can lids or pool covers — also can help, as can treating water in birdbaths and landscaping pools with “mosquito dunks” available at hardware and farm stores.

“August and September are always bad mosquito months,” Fryxell said.

Source: Knox

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