West Nile virus under microscope at university

ST. LOUIS -- Even as scientists were confirming that the West Nile virus had reached St. Louis, researchers here already have been trying to pinpoint why the mosquito-transmitted form of encephalitis makes only a fraction of those infected seriously ill.

And why even fewer die.

"We don't know which part of the immune system is primarily responsible for combating the virus," Michael Diamond, an infectious-disease microbiologist who leads the study at his Washington University lab, told the St. Louis Post-Dispatch for a story Sunday. "Once we understand that, then we can begin to predict who is at risk for the virus."

On Friday, state and area health officials announced that the virus has been found in five dead crows around St. Louis. No human cases of the virus have been reported regionally.

The discovery of the birds -- found dead between Sept. 15 and Sept. 29 -- came about a month after the virus surfaced in birds around Chicago as part of what scientists considered its westward migration.

Mosquitoes can transmit the disease to human beings from infected birds, although fewer than one in 500 mosquitoes is infected. While the virus is a concern, fewer than 1 percent of people bitten by an infected mosquito become severely ill with encephalitis, or inflammation of the brain.

There have been 100 cases of West Nile virus in human beings since the disease was found in New York in 1999, according to federal statistics. Ten people have died.

The virus -- not found in this country until 1999 -- has been detected in 27 states, the District of Columbia and the Canadian province of Ontario.

Most people infected with West Nile show no symptoms; others can have fever, head and body aches, skin rash and swollen lymph nodes. People such as the elderly or those with weakened immune systems can suffer muscle weakness, convulsions, coma or death. There is no specific treatment for the disease and no vaccination.

Diamond has long studied the virus that causes dengue fever, a close relative of the West Nile virus. The most severe form kills thousands of people each year, mainly in the developing world. Similarities between the two viruses include flulike symptoms.