Experts Anticipate Bad Year for W. Nile Virus

March 28, 2004
Kerry Fehr-Snyder
The Arizona Republic

The unseasonably warm spring weather isn't just causing humans to sweat; it's jump-starting mosquitoes that can infect humans and animals with the West Nile virus.

Health officials are bracing for more cases of the flulike illness, which can be deadly and is expected to make its second appearance in as many years in Arizona. And based on other states that have been dealing with the virus, the second year is the killer - figuratively and literally.

"It's the second year that seems to blossom as a real awful time," said Michael Fink, epidemiologist for the vector-borne and zoonotic disease division of the Arizona Department of Health Services.

For example, in Colorado only 14 people contracted the virus the first year. In the second year, the number grew to 2,945, and 55 people died. While the bulk of the infections in 2003 were among middle-age adults, 67 cases occurred in children younger than 15.

In Arizona, 13 individuals were infected last year and one died, according to the state health department.

West Nile virus typically gives people flulike symptoms, but sometimes individuals can develop an infection of the central nervous system, such as meningitis or encephalitis, affecting the spinal cord and brain. That occurs in about 20 percent of the cases. Elderly individuals are most susceptible.

In an effort to lessen the second-year impact here, Arizona has doubled its surveillance and testing budget for West Nile. It spent about $150,000 last year on the program, which includes tests on human blood to confirm the virus, as well as testing chicken flocks, mosquitoes, horses and dead birds for signs of the virus.

Besides increasing its capacity for surveillance and testing, the state also is spending about $20,000 on radio ads to convince residents that it's up to them to keep the virus at bay by eliminating all sources of standing water around their homes and neighborhoods.

"Pretty much every neighborhood has breeding sites for mosquitoes," said Will Humble, chief of the state health department's bureau of epidemiology and disease control services. "Absolutely the most important thing for people to do is not just go around their house but around their whole neighborhood to eliminate water sources."

Catherine Eden, director of the state health department, said residents also should take precautions when outdoors by wearing insect repellant, especially at dawn and dusk, when the West Nile virus-carrying mosquito is active.

"We're really pushing people to wear repellant," she said. "We can't predict with certainty (the upcoming season), but if we just observe from other states, we can only prepare. Most people infected with the virus won't be sick. But we want people to take this seriously because it will probably be worse than last year."

The virus also affects animals, especially farm animals that spend time outdoors near sources of water that breed mosquitoes. The virus originates in birds, which are fed on by mosquitoes. An infected bird passes the virus to the mosquito, which then passes the virus to healthy birds, animals and humans after a blood meal.


TESTING CHICKENS

Chickens, which have developed antibodies to the virus, are used as sentinels. Health officials take blood samples from chicken flocks throughout the season to get an early warning the virus is present.

Horses also become sentinels but can be vaccinated against the virus and other related viruses, including St. Louis encephalitis and western equine encephalitis. About 30 percent of all horses that become infected die. Those that survive can develop so-called "sleeping sickness" and can suffer mental deficits, making them unusable as working horses or studs.

Dr. Richard Rezzonico, a veterinarian in Phoenix, said he has been working furiously to vaccinate horses against West Nile virus. The vaccine is a series of two shots, several weeks apart. There is no vaccine for humans.

"People are starting to get excited with the warm weather," he said. "They're starting to see mosquitoes, which we usually don't see until June, May at the earliest."

Whether the season will turn out to be bad for horses will depend, Rezzonico said.

"Our incidence here (in Maricopa County) is going to be dependent on rain. If we get rain now, it'll be bad," he added.

West Nile was first detected in North America in 1999. It has made a steady march westward and was detected in 44 states and the District of Columbia last year.

In general, the second year after the virus was first detected in each of those areas turned out to have more cases.

Health officials aren't sure why, but the third year of the virus has turned out to be less severe. They hypothesize it may have something to do with birds developing some sort of immunity.

Yuma County health officials have had a false alarm this year after receiving a report of a case. Tests at the state lab later showed the report was due to a false positive.

"That was a sigh of relief," said the state health department's Fink.

Yuma has a nearly year-round mosquito problem because of its location at the confluence of the Gila and Colorado rivers. Sinkholes that fill with water overnight become major breeding grounds for mosquitoes.

The state health department expects to begin accepting mosquito samples for testing April 15.

That's 15 days earlier than last year.

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