An avid outdoorsman, Mark Davis knew he would one day be bitten by a mosquito carrying the West Nile virus. He also knew he would probably come down sick from it to some degree.

What the Saratoga resident didn't realize was how long the nagging flu-like symptoms would last.

It's been almost three years since he and his wife, Janice, became sick from the mosquito-borne West Nile virus. They are both still battling the sickness, although Mark Davis has much worse symptoms than his wife.

At first, doctors told him he probably would recover in three or four months, the usual recovery time for West Nile fever.

"When I did get it I thought, 'OK fine, good. Let's get it over with,'" he said.

"Now they tell me I may never get over it."

There is no vaccine or cure for the two illnesses that can stem from the West Nile virus: West Nile fever or the life-threatening West Nile neuroinvasive disease. At this point, Mark Davis says, doctors don't know which form he has.

Those who come down with the milder, more common West Nile fever usually suffer from flu-like symptoms and fatigue for three to four months. West Nile neuroinvasive disease is an infection of the nervous system that some people develop from the virus. It is a much more serious illness than West Nile fever and can lead to paralysis and death.

For most West Nile fever patients the only way to recover is to rest and wait it out. Almost three years later, the Davises are still waiting.

Mark Davis is thin as a rail and can't put on weight. He worries he may die from the disease.

Dr. Tracy Murphy, state epidemiologist for the Wyoming Department of Health, said the virus affects different people in different ways.

"A significant number of people who had the severe (neruroinvasive) disease, a significant proportion of them can have long term or even permanent disabilities or effects. That number may be up to even 50 percent."

Mark and Janice Davis, who each show varying symptoms of West Nile fever, are unusual in that their illnesses have lasted so long.

"Usually that is seen in the more severe disease (the neuroinvasive form). But even with the less severe West Nile fever illness, people will report lingering fatigue and weakness for several months."

Only one in 150 people infected with West Nile virus ever develop a severe illness. Only about 20 percent of the people infected ever develop mild symptoms.

The rest never become sick at all. The virus cannot be passed from person to person but it is possible to contract it through a blood transfusion.

Mark and Janice Davis contracted the virus while on a fishing trip in northern Colorado in August 2004.

His wife's illness began with a terrible headache about a week after they returned home from the trip. A few days later he woke up in the middle of the night with chills and a fever, and felt so weak he couldn't walk.

"I crawled in and out of the doctor's office," he says. "Literally I was on my hands and knees… We spent the next 10 months so tired you're just sitting there trying to get enough energy to walk 30 feet to go to the bathroom."

The painful headaches still come and go for Janice Davis but for the most part she says she's feeling better. Mark Davis, however, still battles chronic fatigue, muscle weakness, head and body aches, stiffness, irritability and other nagging symptoms that come and go from day to day and week to week.

It's like having the flu and never getting over it.

Some days he feels well enough to go to work down the street at the local fly shop or to take a short fishing or hunting trip. But other days he feels so sick he can't get out of bed.

Doctors seem powerless to help and can't explain why he isn't getting over the illness, he says.

"I feel like it's aged me 10 years."