Clark County mosquitoes were found to be positive for encephalitis, health officials have reported.

Pools of mosquitoes from four zip codes — 89191, 89146, 89120 and 89104 — were found to have St. Louis encephalitis. The county has not reported any human infection of the virus since 2007.

Southern Nevada Health District chief officer Joseph Iser assured residents that they should not worry about the existence of the rare disease, but they should be aware that such exists in the county. Mosquitoes in Clark County do not often test positive for St. Louis encephalitis. Since 2004, the health district has been conducting vector surveillance programs, and the only time they found an infected mosquito pool was in 2005.

Iser attributed the rise in infected population to the concurrent increase in the number of visiting birds that infect the local mosquitoes. Iser added that the groups of mosquitoes found positive will be terminated as a means of precaution.

Nevada State Infectious Disease Forecast Station director James Wilson said the St. Louis encephalitis' mosquito-to-human transmission reaches its peak in Nevada in August. He agreed that the result is nothing to worry about, as infected mosquitoes are fairly common around the county during this time.

"It's an early warning indicator telling people to watch out around areas where there are mosquitoes," said Wilson.

The health district's efforts toward mosquito testing and surveillance are heightened as a response to the incidence of Zika virus and West Nile virus. While the mosquito pools have not tested positive for the said viruses, the health district has reported five cases of travel-associated Zika infection.

What Is St. Louis Encephalitis?

St. Louis encephalitis is a vector-born Flavivirus infection transmitted by infected mosquitoes to humans. It is similar to West Nile virus, dengue virus and yellow fever virus.

Many individuals with the infection do not show apparent signs of the illness, but early symptoms could include headache, fever, nausea and vomiting and fatigue.

Older adults are often the ones infected with the neuroinvasive disease, which causes brain inflammation or encephalitis. There were reported cases of prolonged disability and death from the infection. To date, there are no available treatments specific for St. Louis encephalitis. Patients with the infection are afforded with symptomatic care.

The Centers for Disease Control and Prevention advises individuals in areas with high concentration of mosquitoes with encephalitis to wear protective clothing and use insect repellent.

Photo: Miika Silfverberg | Flickr

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