NILE, Wash. -- In a lifetime of raising horses, 72-year-old Keith Morris had never seen anything like it.

Seemingly overnight, his 4-year-old quarter horse became paralyzed in the hind legs.

"It pretty much came on all at once," said Morris, a Nile rancher. "She was healthy the day before, but then she couldn't move."

Tests confirmed it was West Nile virus, which can cause encephalitis, or inflammation of the brain and spinal cord, destroying the central nervous system.

The horse didn't recover and was euthanized two weeks ago.

"She was kind of a special horse," Morris said.

The loss prompted him to vaccinate his other 22 horses, but he's still scratching his head over the odds that the virus found its way to this tiny valley above Naches.

The Nile, he thought, would be the last place to see West Nile virus.

"We just never had any of this before," Morris said.

But the mosquito that stuck its virus-laden proboscis into Morris' horse is just one of many that have found hospitable breeding grounds in Yakima County in recent years.

In fact, mosquitoes -- which get the virus from feeding on dead birds -- have made Yakima County a hot spot for West Nile virus.

Last year, the county led the state with 26 confirmed cases in horses. The year before, there were eight cases statewide -- all of them in Yakima County.

Officials aren't yet sure about this year's trend, but so far, the county has had six horse cases out of 21 statewide. Only Benton County has more, with nine cases. The other cases are scattered throughout Benton, Kittitas, Grant and Adams counties.

Last year at this time, there were eight horse cases statewide.

"I think we're going to get hit pretty hard this year," said Leonard Eldridge, state veterinarian. "Do the mosquito control, 'cause the dang things carry it."

Two suspected human cases of the virus have been reported this year, both residents of Prosser.

Health officials don't release the names of victims, but one of them, Paul Champoux, the owner of Champoux Vineyards, notified his fellow grape growers of his illness in an e-mail. Champoux was hospitalized in Richland and suffered partial paralysis for several days.

The state Department of Health is conducting its own laboratory testing and has not yet confirmed that either person became ill as a result of West Nile virus.

The virus was first identified in 1937 in a woman from the West Nile district of Uganda. It didn't appear in North America until 1999, when it was seen in both horses and humans in New York state.

The virus spread from east to west, finally hitting Washington in 2002, then skipping three years before it showed up in mosquitoes near Grandview and Prosser.

It has remained primarily a disease that attacks horses. While 30 percent of horses that become ill from the virus die, the vast majority of people who have it -- four out of five -- never get sick or show symptoms, according to the federal Centers for Disease Control and Prevention.

Experts aren't entirely certain why Central Washington in general and Yakima in particular seem to have the most cases. Mosquitoes aren't exactly the state insect in this arid climate.

But Tim Baszler, director of the Washington Animal Disease Diagnostic Laboratory at Washington State University in Pullman, said hot temperatures and standing water are ideal for breeding the bugs. Mosquito larvae don't easily hatch in running water.

Horses and pastures with troughs of standing water create a perfect environment for mosquitoes with the virus to replicate, he said.

"Animals tend to congregate around water," Baszler said. "The drier it is, the less water, but the more the animals concentrate around that water."

Baszler said normally, as the virus becomes endemic to an area, the numbers of reported cases go down. That's because people and animals develop an immunity.

"The last four years we've had increasing numbers of cases in horses. It seems like its not going down," Baszler said.

Baszler said most of the cases occur in horses that have not been vaccinated.

Some veterinarians say horse owners may think their animals are already immune or find the vaccine too costly. A single dose can cost up to $25 retail, and some require two doses and a booster every spring. Veterinarians may sell the vaccine without the retail markup.

Equine vets in the Yakima Valley differ on whether a veterinarian should administer the vaccine, which obviously adds to the cost.

Ernie Munck of Prosser said anyone comfortable vaccinating their horse should do so.

"If a person feels capable of giving an injection, I encourage that," he said.

But Lutz Harfst of Yakima said there are good reasons to let the vet do the job.

"We use a vaccine people can trust and we know how to do it right. Plus, I am computerized so when I do it, it's documented," Harfst said.

Above all, both vets encourage vaccination because a horse with full- blown West Nile will suffer. And they point out that it's not too late in the season to vaccinate. The virus will be around through September and even into October.

Harfst said it can be difficult to tell when a horse is suffering.

He recalls a client who detected a slight tremor in her horse's face that looked harmless enough. But sure enough, the horse had the virus.

"It comes in many different shapes," he said.

Munck has seen horses go down and never get up. Others seem to fight the virus.

"The first case I ever saw was a mare that acted like she didn't want to walk because she was afraid she was going to fall. She just stood there and eventually recovered," he said.

If a horse does fall sick and doesn't recover, euthanization can cost upwards of $3,000.

That's one of the reasons Keith Morris vaccinated his herd.

"I can't afford to lose any more horses," he said.

* Leah Beth Ward can be reached at 509-577-7626 or lward@yakimaherald.com.

Warning signs

Although most cases of West Nile virus in Yakima County involve horses, people can also get the infection from mosquito bites. Here are the facts about human West Nile virus:

* Mild symptoms are fever, headache, body aches.

* Serious cases involve encephalitis, infection and inflammation of the brain and spinal cord.

* There is no cure.

* There is no vaccine for people.

* It is not communicable human-to-human or horse-to-human or even between horses.

* Once you have had an infection, you are likely immune for years.

* Eighty percent of people who contract the virus don't have symptoms.