Mosquito Sample Tests Positive-WNv

March 22, 2011, 9:02 a.m.

March 16, 2011

A case of West Nile virus has been found in a mosquito sample tested in January, providing significant information about how the virus outlasts the winter, a recent St. Tammany Parish Mosquito Abatement District report stated.

Times-Picayune archiveA mosquito feeds on a human hand. A test sample returned positive for West Nile, giving new evidence that the virus cycles as normal during the winter months.

The virus was found in the mosquito Culiseta inornata, a species normally active in the winter and early spring. This is the first time the species has tested positive for West Nile, the report said.

A total of 96 mosquito samples were tested for the virus in January, with one Culiseta inornata pool returning positive, the report said. A mosquito sample typically consists of up to 50 mosquitoes that are tested as one unit.

According to Charles Palmisano, director of the mosquito abatement district, the new evidence backs suspicions the virus actively cycles - via infections between mosquitoes and birds - instead of lying dormant during the winter when cold temperatures slow mosquito activity and development.

"It's just another piece of the puzzle to the question of what happens to the virus in the winter," Palmisano said. "While this indicates the (infection) cycle could be continuing during the winter, we aren't sure what effect this could have in late spring, early summer."

No human cases of West Nile have been reported this year, and once weather permits and adult mosquitoes become more active, the district will begin spraying ditches in the parish to control the mosquito population, Palmisano said.

"The spring is a very important time of year to hopefully have an impact on West Nile virus activity for the entire year," Palmisano said. "Our thinking is that if we can reduce the viral activity in the early spring, perhaps this will also reduce its impact during the summer when human transmission is most likely."

Through Feb. 21, there have been no other positive findings for West Nile, Palmisano said.

About 90 percent of the people who contract West Nile will never experience any symptoms and likely will never know they have the disease, officials have said. Nearly all the rest will suffer from West Nile fever, which has symptoms similar to the flu and is not typically diagnosed as West Nile.

Only about 1 percent of patients who contract West Nile will develop the neuroinvasive form of the disease that can result in brain or spinal swelling leading to permanent damage or death. People who are at least 65 years old are the most likely to suffer complications.

When a mosquito feeds on a bird infected with West Nile, the mosquito can carry the virus and infect a person through a bite. It is not transmitted from person to person.

Jake Clapp can be reached at

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