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West Nile Warning: Mosquito Season Approaching

Late last summer, Randy Glover thought he was going to die; at times, he wanted to die. The resident of rural Billings, MT, was suffering from West Nile virus (WNV).

"There were times in the hospital I wanted to ask the nurse for a gun," says Glover, 46. "It's impossible to describe how hard this disease can put a person down."

While Glover still isn't fully recovered, he's gained back the 25 lbs. lost during the worst sickness of his life. Now, he's concerned about the coming summer and whether his family and neighbors will avoid exposure to the disease. He's hopeful the "numbers" work in their favor.

The U.S. Centers for Disease Control (CDC) says only about one in 150 people infected with WNV develop severe illness. The symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. The symptoms can last several weeks, and neurological effects may be permanent.

"About 80% of people bitten by an infected mosquito won't become sick, but others may experience a mild, flu-like illness," says Leslie Tengelsen, MD, Idaho deputy state epidemiologist. "Although rare, the virus can lead to serious illness, especially in people over 50."

Glover can attest that the mere presence of WNV in a community is a serious matter. As the summer season approaches, he sternly warns anyone who works or plays outdoors where the disease has been detected: "Do everything you can to avoid getting bitten by mosquitoes."

WNV was first isolated from an adult woman in the West Nile District of Uganda in 1937, and spread into Egypt in the 1950s. The virus was recognized as a cause of severe human meningitis or encephalitis in elderly patients during an outbreak in Israel in 1957. Equine WNV was first noted in Egypt and France in the early 1960s.

WNV caused a great deal of alarm when it first appeared in the U.S. the summer of 1999. It spread across the continent and is now permanently established in the Western Hemisphere. Since 1999, WNV human, bird, veterinary or mosquito activity have been reported from all states except Hawaii, Alaska and Oregon.

Of the 4,219 human cases in the U.S. last year, 2,616 (62%) were reported as West Nile fever; 1,433 (34%) as West Nile meningitis or encephalitis; and 170 (4%) as clinically unspecified. CDC says 161 human fatalities were attributed to WNV in the U.S. in 2006, with 29 deaths in Texas, 16 in Idaho, 14 in Mississippi, 11 in Arizona and nine in Illinois.

Statewide surveillance efforts and educational campaigns are being ramped up nationwide to raise awareness of WNV among healthcare professionals, local health officials and all citizens -- especially those in rural areas where the majority of WNV cases seem to appear.

Most health authorities suggest the mosquito-borne virus usually takes a heavier toll the year after it first shows up in a region. When the disease appeared in Colorado in 2002, for instance, only 14 human cases were reported there. But the next year, 2,947 human cases and 63 deaths were reported. In 2004, there were 288 cases and three deaths in Colorado.

Horses and humans are the most likely mammals to show signs of disease. For more on horses and WNV, read Pennsylvania State University Extension horse specialist Ann Swinker's article at

"The best way to protect a horse from WNV is vaccination," says Leonard Eldridge, Washington state veterinarian. The vaccine requires two doses, three to six weeks apart, with immunity achieved five weeks after the second vaccine. He recommends an annual booster prior to the start of mosquito season.

To date, the only sign of WNV in cattle is antibody titers specific to the virus, says Kent Anderson, DVM, Valleywide Veterinary Services, Cornwall, VT.

"This is indicative of an immune response. So far, no exposed cows have shown any evidence of illness or clinical disease," Anderson says. "It remains extremely unlikely this virus would be the cause of sickness in the bovine species."

However, WNV infections have been documented in other mammals -- cats, dogs, sheep, goats, bats, llamas, wolves and rodents.

"To the best of our knowledge, mammals are dead-end hosts, meaning that they don't transmit the virus to each other," Anderson explains. "Infection only occurs via the mosquito, which must gather the virus from a bird and inject it into a mammal."

Anderson says WNV fever should remain very low on the bovine veterinary diagnostic list.

"Be that as it may, any evidence of neurological disease in cattle should be seriously considered," he notes.

Because rabies, BSE, pregnancy toxemia, listeriosis, tetanus, poisoning, botulism, meningitis, grass tetany, encephalitis, etc. all share some symptoms, producers should isolate the animal, prevent exposure to body fluids and contact a veterinarian.

Because mosquitoes play such a dominant role in transmission, health officials stress elimination of standing, stagnant pools of water conducive to mosquito reproduction.

Marilyn Roossinck of the Plant Biology Division of the Noble Foundation, Ardmore, OK, suggests spraying exposed skin with a strong insecticide before going outside, especially early in the morning and later in the day. And wear long-sleeved shirts and pants to help protect skin from mosquito bites.

Stephanie Etter, Extension livestock education specialist, Wilder, ID, has seen the effect of WNV in her area. Idaho's Snake River Valley has been a recent hot spot for the disease. The area -- with vast amounts of irrigated farmland -- is typical of regions where WNV finds a home.

"Several of our 4-H and FFA members have come down with WNV -- in some cases, some very devastating sicknesses," she says. "One of our FFA members ended up in the hospital in a coma." The young man has since recovered.

She says these are otherwise healthy, active younger people who don't fit the demographic groups normally associated with WNV sicknesses.

Etter is adamant that agriculturists learn all they can about the disease and work to reduce mosquito populations and protect themselves from mosquito bites.

"This disease is nothing to fool around with," she adds. "It's one of those things where you don't know it's in your area until it's too late. And the impacts can be enormous."
-- Clint Peck

TAGS: Parasites