Number of West Nile virus cases rising


SALEM, Ohio – In late June, the first pool of mosquitoes to test positive for West Nile virus was confirmed in Ohio, making it only the second state to confirm the virus in a pool this year.

As of July 11, the state department of health also confirmed 124 cases of the virus in dead birds from 41 counties this year. One live bird tested positive in Franklin County.

Pennsylvania Health Secretary Robert Zimmerman confirmed crows in two of the state’s counties tested positive July 5.

The numbers reflect a growing presence of West Nile virus in Ohio and Pennsylvania as the disease moves westward, leaving no county or town immune to the threat.

Confirmed cases. The American crows confirmed in Pennsylvania were found in Lehigh and Delaware counties in the southeastern part of the state.

Prior to that, two others tested positive in Lehigh County, and others were found in Chester and Bucks counties, bringing the state total to six.

“Though we haven’t found anything there yet, we’ve got to assume that the disease is in every county,” said Richard McGarvey, spokesperson for the Pa. Department of Health, noting the disease has been found in all corners of the commonwealth.

Mosquitoes. The positive Ohio mosquitoes were found in a trap in Cuyahoga County, according to Richard Berry, chief of the state department of health’s Vector-borne Disease Program.

Berry said finding the virus in mosquitoes this early in the year indicates the virus is spreading in Ohio, and Pennsylvania officials have noticed the same trend.

“We found cases of the disease up to two months earlier than normal this year,” McGarvey said.

“The larger mosquito population, thanks to much more precipitation this spring, has grown because of standing water everywhere,” he said.

Both states instituted surveillance programs to help detect the disease and created guidelines for mosquito control. Mosquito spraying is done on a local basis.

Pennsylvania officials continue to emphasize larvae control with ground spraying in areas of high mosquito concentration, according to McGarvey. Last week, state Department of Environmental Protection workers sprayed three Crawford County communities where sampling showed unusually large numbers of mosquitoes. Areas affected included parts of Meadville, and in Vernon and Hayfield townships.

West Nile surveillance teams found as many as 1,000 adult mosquitoes in traps in the area sprayed compared to 50 to 100 mosquitoes last year during the same period.

“We can stop them at [the larvae stage]. It’s much easier than when they’re on the wing,” McGarvey said.

Ohio suspicions. The Ohio Department of Health’s Vector-borne Disease Program has tested more than 530 dead suspect birds and more than 200 live birds this year, including crows and blue jays.

During the week of July 8, 11 blue jays, crows or grackles tested positive.

More than 21,000 mosquitos were tested and six positive pools – groupings of between 1 and 50 mosquitoes of the same species collected at one location – were identified.

In addition, 20 humans tested negative.

Growing threat. Prior to August, 1999, no West Nile virus cases had been reported in the United States or Western Hemisphere.

During the 1999 outbreak, 62 people, including 46 residents of New York City, became ill. Seven people died of West Nile virus-related infections during this initial outbreak.

In 2000, there were 21 diagnosed cases and two deaths. In 2001, there were 66 diagnosed cases and nine deaths nationwide, and the virus was identified in 27 states.

Equine threat. In 2001, 738 cases of horses infected with West Nile Virus were reported in 20 states nationwide, including seven cases in Pennsylvania. Of the seven, four died or were euthanized.

As of June 12 this year, seven equine cases have been reported in Florida and three in Louisiana. Texas and Kentucky each reported its first-ever case of the disease in a horse in early July.

The disease has also been detected in Canada, Connecticut, Florida, Georgia, Illinois, Louisiana, New Jersey, New York, Massachusetts, Michigan, Pennsylvania, Tennessee, Virginia, and in the District of Columbia.

The Ohio Department of Agriculture has tested 11 horses for the disease, and none tested positive.

While a vaccine is available for horses, the animal must receive two doses of the vaccine three to six weeks apart, and full protection does not begin until at least four to six weeks after the second dose of vaccine is administered.

Mild symptoms. Primarily a wild bird disease, West Nile is a mosquito-borne virus that generally causes mild symptoms that mimic the flu in humans.

West Nile virus is spread to humans by the bite of an infected mosquito. When a mosquito bites a bird that carries the virus, the mosquito becomes infected.

Once a mosquito is infected, it may transmit the virus to people or animals when it bites them.

Many birds can be infected, but crows and blue jays are most likely to die from the disease. Horses are also prone to West Nile virus infection.

People cannot get West Nile virus directly from another person who has the disease.

The virus can cause encephalitis, an inflammation of the brain, or meningitis, inflammation of the covering of the brain and spinal cord, in humans.

(You can contact Andrea Myers at 1-800-837-3419, ext. 22, or by e-mail at


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