Virus that causes encephalitis found in migratory mallard

Tuesday, June 28, 2005 | 11:13 a.m.

Blood from a migratory mallard duck passing through Clark County has tested positive for St. Louis encephalitis, the Clark County Health District announced today.

The virus that causes St. Louis encephalitis is spread through the bites of mosquitos feeding off birds that carry the virus. Birds do not get ill from it because their immune systems protect them, health officials said. The virus can make humans ill, but infection in humans is rare.

Only three human cases of St. Louis encephalitis have been reported in Nevada since 1964, according to the U.S. Centers for Disease Control and Prevention in Atlanta.

No mosquitos infected with St. Louis encephalitis have been found in Clark County this year, officials said.

The exact location of where the bird that tested positive for St. Louis encephalitis was found was not immediately released.

Health District spokesman David Tonelli said the bird in question was tested by the Nevada Department of Agriculture's Animal Disease Laboratory and, per procedure, was released prior to the test results being known.

Blood was collected from a 5 percent sampling of birds in an area on June 13 and the results of those tests came back this week, Tonelli said.

"The important thing for us to know is that there is activity with this disease," he said. "When it shows up in birds, it generally will later show up in mosquitoes."

Clark County and the Agriculture Department sample bird populations as part of a cooperative agreement to determine whether birds are afflicted either with St. Louis encephalitis or West Nile virus. There has been no West Nile virus detected in Clark County this year to date.

Last year, there were 20 confirmed cases of West Nile virus locally, but no deaths.

This is the first time in many years that St. Louis encephalitis has shown up in Clark County, though mosquitos tested in Fallon recently were found to be positive for carrying the disease, according to the Nevada Department of Agriculture.

Last August, the Nevada state laboratory confirmed that mosquitoes collected near Fernley in Northern Nevada's Lyon County tested positive for St. Louis encephalitis.

The county also traps and tests mosquitos for Western Equine encephalitis, but none have tested positive so far this year, officials said.

The Health District recommends that people protect themselves from mosquito bites by applying insect repellent containing DEET (N-diethyl-meta-toluamide) or repellents containing Picaradin or oil of lemon eucalyptus.

The Health District also recommends wearing long pants and long-sleeve shirts, avoiding spending time outside at dusk and dawn when mosquitos are most active, repair areas where there is standing water and make sure windows and doors have tight-fitting screens without holes.