West Nile virus expected to reach Nevada by spring

William McCall

Friday, Jan. 17, 2003 | 11:16 a.m.

PORTLAND, Ore. -- Nevada is among the last few states untouched by the West Nile virus, but health and veterinary officials said Thursday they expect to see cases of the potentially fatal disease in animals -- and possibly humans -- by spring.

The virus is transmitted by mosquitoes and was first reported in the United States in 1999 in New York. It has since spread to 43 states and the District of Columbia, according to Dr. Anthony Marfin of the Centers for Disease Control.

The handful of states with no reports of the disease so far are all in the West: Oregon, Idaho, Utah, Arizona, Nevada, Hawaii and Alaska.

West Nile virus can be fatal to humans, domestic animals and wildlife if it triggers encephalitis -- inflammation of the brain -- or meningoencephalitis, when the inflammation includes the spinal cord.

In the 1999 outbreak, 62 people were infected and five died. By the end of 2002, nearly 4,000 cases had been reported nationally with 252 deaths.

Marfin said the disease is a serious threat but deaths still are rare.

"Let's say 150 people are infected -- 120 people will show absolutely no symptoms at all, and maybe only 10 to 20 will get the fever and other symptoms of the virus," Marfin said. "Only one or two people will get encephalitis, and the death rate for encephalitis is about 10 percent to 15 percent."

The disease is concentrated among birds but also affects horses and other mammals. There is no human vaccine but there are vaccines to protect animals.

Biologists and veterinarians attending the conference sponsored by the Audubon Society and the Oregon Zoo said they can take steps to protect domestic animals, including vaccination.

They said they were concerned about the effect of the disease on small populations of wild birds and animals, particularly birds of prey such as owls, eagles and California condors.

"The great horned owl really took a beating in the Midwest," said Dr. Marli Lintner of the Avian Medical Center in Portland.

She told the conference of about 250 animal and human health experts that she is not recommending vaccination at this point but extra precautions are needed this year to protect people and animals from mosquito bites and possibly other insect bites.

"There is some evidence from Canada that biting flies can also transmit West Nile, and it seems to be a pretty sturdy bug, so I can tell you that I don't want anything biting me this year," Lintner said.

Birds, especially crows, jays and magpies, are most susceptible and often are the first indicators the virus has spread.

Mace Vaughan of the Xerces Society -- named for the first butterfly species on record forced into extinction -- warned against overreaction with toxic pesticides to kill mosquitoes, part of the food supply for many birds and other animals.

He cited a national study by the Harvard School of Public Health released this month that indicated wide public support for mosquito spraying despite concerns about environmental and health effects.

"The key is a targeted approach," Vaughan said, adding that the greatest threat is typically in cities where water pools around buildings, houses and other structures to create miniature mosquito breeding grounds to put the insect close to humans.

A study for the Mississippi State Department of Health suggested that living near abandoned buildings increased the risk of being infected fourfold while standing water, such as puddles or decorative ponds, increased the risk of infection eight times.