2006 record year for West Nile virus

A record 123 human cases of West Nile virus were confirmed in Nevada in 2006, just one of those in October in Pershing County. The figure doesn't jibe with what was seen last year, when almost 25 percent of the cases were diagnosed in October, according to figures from the Nevada State Health Division.

Dr. Anette Rink, director of Nevada's animal disease and food safety lab in Reno, said the only predictable thing about West Nile is its unpredictability.

"Not a single year was predicted correctly on the East Coast," she said.

"We were expecting last year to be a record year with respect to West Nile virus in Nevada. It was our second or third year after the virus was introduced and we had a lot of precipitation," she said. "It (2005) was an excellent mosquito year and we expected West Nile to be prevalent throughout the state, but it didn't happen."

Nevada had an abundance of mosquito breeding sites in 2006, together with warm temperatures. The disease was much more prevalent and hit us hard this year, Rink said.

"We had a second winter with a lot a precipitation," she said. "We're still seeing water in areas throughout the state that are normally dry by May."

According to statistics from the Centers for Disease Control and Prevention in Atlanta, neighboring Idaho had more human West Nile infections than any other state, a total of 824 confirmed cases. Colorado came in second with 310 cases, Texas had 290 and then California, with 257.

Rink believes surveillance and abatement practices played a key role in the difference between Nevada and Idaho.

"A significant number of cases were prevented in Nevada," she said. "It could have been a lot worse."

Mosquito Control Officer Ron Lynch said no larvae have been detected since the recent hard freezes.

"That stopped things pretty good for now," he said "I think we're OK."

Geography seems to have little to do with the frequency of cases. Through Oct. 24, Arizona confirmed 120 cases of West Nile while neighboring New Mexico confirmed just four.

In Nevada, Clark County only had 3 cases, while cow counties like Douglas, Humboldt and Elko, had significantly more cases per capita.

Rink said the amount of precipitation, and subsequently the number of mosquito breeding sites, played a key role.

"Southern Nevada didn't get the type of precipitation the rest of the state got," she said.

Like other arboviruses, West Nile is spread through a bird-mosquito cycle and transmitted to mammals, including humans, through the bite of an infected mosquito.

Mosquitoes are infected by taking a blood meal from infected birds.

West Nile virus primarily affects birds, humans and horses, and to a lesser extent other domestic animals such as sheep, goats, dogs and cats.

It was first detected in North America in 1999 in New York and since then, has steadily moved westward.

In Nevada, the Animal Disease Laboratory has been conducting surveillance testing for the disease on a variety of species since March 2001. West Nile was first detected in Nevada in a crow found in Carson City on July 15 2004, according to information from the Nevada Department of Agriculture.

Susie Vasquez can be reached at svasquez@recordcourier.com or 782-5121, ext. 211.