West Nile virus appears to be heading West. (Summer Forecast 2003).

West Nile virus may march westward during the summer of 2003, promulgating disease in record numbers in the Great Plains, the West, and Alaska, two Harvard University investigators predict.

In the meantime, physicians are urged to stay alert to the possibility of diagnosing West Nile virus in their patients, even if the virus has not been a factor in their communities in previous years.

West Nile cases in wild and domestic birds and mammals have already been confirmed across the southern United States, Michigan, and Minnesota. And two suspected human cases of West Nile virus from Louisiana are being investigated by the Centers for Disease Control and Prevention as a possible indicator that the 2003 West Nile virus season has already begun.

"In 2002, West Nile virus made a furious dash across the nation during what was a hot, dry summer, spreading to 44 states, the District of Columbia, and 5 Canadian provinces," said Dr. Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard University, Boston, during a press teleconference in mid-May

This year, states previously spared or barely affected by West Nile virus--Utah, Nevada, Colorado, Arizona, New Mexico, California, Oregon, Washington, and Alaska--may be particularly vulnerable to the mosquito-borne illness because of warmer-than-normal winter conditions followed by heat waves and drought in the spring and summer, he said.

The same weather conditions prevailed in New York City in 1999, when the virus in the Flaviviridae family first emerged in North America, heralded by dead birds, ailing zoo animals, and illnesses in 62 people, 7 of whom died. After several rather mild West Nile virus years, the virus seemed to take hold across the United States last summer, a season plagued by drought after a mild winter.

Reported cases totalled 4,156, and 284 people died.