The signs of West Nile virus (WNV) are similar to enteroviral meningoencephalitis. Diagnosis can be made retrospectively by sending a serum sample to the State Hygienic Laboratory. There is no specific antiviral therapy at this time, and there is no WNV vaccine for humans. (There is a WNV vaccine to protect horses.)

For healthy children, adolescents and younger adults, there appears to be little or no risk from WNV infection. As with other viruses a natural infection early in life will protect the person from a life-threatening infection in late adulthood.

At least one case of congenital WNV infection has been detected in a newborn, whose mother was infected during pregnancy. The mother was never seriously ill.

Some background on West Nile virus

The West Nile virus is in the family of Flaviviruses. Famous members of this family cause dengue fever, yellow fever and Japanese encephalitis. Many of these viruses are carried by mosquitoes. Yellow fever is renowned because it was one of the reasons the Panama Canal project was such a difficult task. Japanese encephalitis virus continues to be a feared virus in many countries in Asia. There are now vaccines that will protect humans from disease following infection with either of the last two viruses.

WNV first was detected in the United States in 1999. WNV was discovered after several elderly people died from meningo-encephalitis. The people lived in and around New York City. The geographic source of this virus has not been determined. Since WNV originates from Africa, one reasonable possibility is that the virus was imported into the United States within exotic birds, such as parrots, imported from Africa for pet shops in New York. The infected exotic birds would transmit the disease after being bitten by mosquitoes. In turn, the mosquitoes would transmit the virus to birds native to North America. Crows appear to be particularly susceptible and may die from WNV infections. When infected crows are bitten by mosquitoes, in turn, the mosquitoes can transmit the disease to humans.

The WNV has now spread along the East Coast and also westward to Illinois and Iowa. There were about 4,000 human cases of WNV disease in the United States in 2002. Chicago was especially affected. In all likelihood, the number of cases in Iowa and Illinois will increase this summer.

The elderly are especially prone to develop severe disease. Because WNV poses a serious health risk to the elderly, they, too, should follow the precautions noted above:

• Always apply mosquito repellant before spending time in outdoor areas where mosquitoes are plentiful.
• Avoid mosquito-infested areas altogether in early evening, when mosquitoes are especially active.