Washington hasn’t seen West Nile in humans

SEATTLE – Washington may end the year as the only Lower 48 state with no cases of West Nile virus, health officials say.

“It’s very bizarre,” said Dr. Jo Hofmann, senior epidemiologist for the state Health Department. “We have no idea why we were spared.”

The virus, spread by mosquitoes to humans from infected animals – mostly birds – has killed 73 people nationwide so far this year.

West Nile infections have been confirmed in more than 2,200 Americans. But because most of those infected don’t get sick or show symptoms, the actual number is likely much greater.

The virus attacks the central nervous system. Some experts say it appears to cause lasting neurological damage in about one-third of the survivors.

It was first detected in the United States in 1999 in New York City. Most states now deal with it as an established human health threat.

Oregon and Idaho reported a few human cases this year and dozens of infected birds and horses. But in Washington, there’s still no sign of the virus.

Public health officials here have been testing blood donors, horses with apparent symptoms, about 500 dead birds – crows, magpies, ravens, raptors and Steller’s jays – and more than 40,000 mosquitoes.

“None of our indicators show presence of the virus,” said Tom Gibbs, director of West Nile environmental surveillance for the Health Department.

That’s especially odd because the virus was found in a few Snohomish County birds and horses in 2002.

“I can’t explain it,” Gibbs said. “Nobody can.”

Dr. Roger Nasci, a West Nile expert at the federal Centers for Disease Control and Prevention’s infectious disease laboratory in Fort Collins, Colo., says it will show up here eventually.

“This is a pretty hot virus in birds,” said Nasci, and birds can cover a lot of ground.

Northern latitudes have shorter mosquito seasons, but that’s no protection – Saskatchewan already has West Nile, he noted.

“West Nile is now one of the most broadly distributed viruses in the world,” he said.

Because of West Nile, many public health officials have resumed tracking animal illness as an early warning system. It’s one of many “zoonotic” diseases – those passed from animals to humans.

West Nile is a flavivirus, a family of viruses that includes Japanese encephalitis, St. Louis encephalitis and dengue.

The search for West Nile in humans continues year-round. But Gibbs will stop animal testing this week because of the cold weather’s suppression of mosquito activity.

Because the virus needs mosquitoes to reach humans, Hofmann said, cold weather makes it “highly unlikely” that anyone in Washington will become infected now.

But Washingtonians sometimes travel to the virus, she noted.

“We did have four people test positive for West Nile this year, but all of them were infected elsewhere,” Hofmann said.

None became seriously ill, and most found out they were infected when they donated blood.