Experts - Mosquitoes may not be sole source of West Nile virus

ST. LOUIS -- Experts gathered in suburban St. Louis reported a surprising finding about the West Nile virus -- mosquitoes may not be alone in transmitting the disease.

The West Nile epidemic is expected to continue spreading west across the United States, experts said Thursday. They also discussed new research indicating that some birds may pass the virus directly to other birds.

Scientists now also suspect that species other than birds may act as a source of the virus.

West Nile virus is known to have infected more than 4,000 people since it emerged in New York in 1999. More than 3,900 people contracted an illness from the West Nile virus last year alone. The Centers for Disease Control and Prevention said that more than 2,300 of those people contracted the most serious form of the disease, a brain-swelling infection.

The CDC attributed 252 deaths to the virus last year, including five Missourians. Most of those who died were people over 60 years old.

The West Nile virus infected animals and birds at unprecedented levels last year, experts say. The virus infected 94 species of birds. Crows and blue jays were the hardest hit. About 77 percent of crows tested were found to carry the virus, and more than 95 percent of the infected crows died, said Robert G. McLean, program manager for wildlife diseases at the U.S. Department of Agriculture's National Wildlife Research Center in Fort Collins, Colo.

Perhaps more alarming, McLean found that crows can transmit the virus from bird to bird in the laboratory.

McLean infected some crows with the West Nile virus and allowed them to mingle with uninfected crows in a free-flight lab. The intentionally infected crows died in about seven days. A few days later, the uninfected crows started to die, too. When McLean examined the animals, he found that they also carried West Nile virus.

The birds excrete the virus in their feces and may transmit it orally to other birds, McLean said. Blue jays also produce large amounts of the virus in all body tissue and feces, he said. Other birds don't appear to excrete the virus, he said.

McLean said he did not yet know if the virus can pass from bird to bird in the wild.

In addition to birds, the virus sickened goats, sheep, reindeer, dogs, seals and alligators. More squirrels than ever also fell victim. West Nile virus was also found in 36 species of mosquitoes, some of which rarely, if ever, feed on birds, said Charles Apperson, an entomologist at North Carolina State University in Raleigh.

The broad range of mosquito and animal species affected by the virus could mean that another animal could act as a source for West Nile virus, Apperson said. Scientists are testing rodents and other small mammals to see if they harbor the virus.

Although the Midwest and eastern part of the United States will probably continue to experience West Nile outbreaks, most of the disease activity will occur in the West as the virus completes its trek across the country, Apperson said.