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West Nile Virus Vaccines Are Relative Success

What protects against a related virus may protect against West Nile, says new research

WEDNESDAY, Nov. 14, 2001 (HealthDayNews) -- Existing vaccines for a related disease could lend some protection against the rapidly spreading West Nile virus infection, Texas researchers say.

The two vaccines, already approved by the Food and Drug Administration, are for Japanese encephalitis (JE). This disease is caused by a flavivirus, a member of the same family as the West Nile virus. In tests, the JE vaccines protected hamsters against the encephalitis associated with West Nile virus infection, Dr. Robert Tesh, a professor of pathology at the University of Texas Medical Branch at Galveston, reported today at the annual meeting of the American Society of Microbiology in Atlanta.

This finding comes just as Massachusetts announced that it has had its first fatality ever from the disease, and New Jersey officials confirmed that one of two West Nile patients there has died. The Massachusetts and New Jersey victims died in the first half of October. The remaining 89-year-old New Jersey patient is in the hospital in stable condition, according to the Associated Press.

West Nile virus, native to Africa, made its first North American appearance in the New York City area in 1999 and hit the elderly particularly hard. About 60 people, whose median age was 71, were diagnosed with it that year; seven of them died. Generally, healthy adults have either no or mild flu-like symptoms. Caused by the bite of a mosquito, it has been spreading south and west ever since. A total of 42 human cases have been reported in seven eastern and southern states this year, with two deaths, the Centers for Disease Control and Prevention (CDC) reports. Infected birds and animals have been reported in 26 states and the District of Columbia this year as well.

There is no available treatment for the infection, whose symptoms include fever, headache, a rash and general malaise. Several laboratories are working on a vaccine. Tesh says he tried two JE vaccines and one for yellow fever against West Nile infections in hamsters because it's known that in some cases, human infection with one virus can help protect against a close relative.

"We wondered what would happen if we used the yellow fever and Japanese encephalitis vaccines," which are flaviviruses, Tesh says. "The yellow fever vaccine didn't work well, but the Japanese encephalitis vaccines protected all the animals. There was less viremia [virus in the blood] and the animals did not get sick clinically."

The hamsters were protected against encephalitis, a brain inflammation that can be fatal, because the antibodies stimulated by the JE vaccines also attacked the West Nile virus, Tesh explains.

"Our thought was that this might be considered as an interim vaccine for high-risk people until a West Nile virus vaccine is developed," he says. "Even when such a [vaccine] is developed, the regulatory process for approval might take several years or even longer."

The JE vaccines probably would be reserved for people at the highest risk of encountering the West Nile virus, such as "workers in diagnostic laboratories, also veterinarians and vector control people," Tesh says. And while most cases of West Nile virus have been reported in older people, "I'm not sure you want to give [the vaccines] to elderly persons, because the risk [of serious illness] isn't that high," he says. "Do you really want to immunize everyone over the age of 55?"

The next step will be to try the vaccines in animals more closely related to humans, such as monkeys, Tesh says. His laboratory is not equipped for such trials, he says, but "the CDC might do it."

The JE vaccine approach is "important and interesting," says Dr. David B. Weiner, associate professor of pathology at the University of Pennsylvania, who is himself working on a West Nile virus vaccine. That work is in its early stages, he says.

"We are using DNA vaccines to provide direct protection," Weiner says. "We reported several months ago that this could provide immunological protection."

The vaccine, which uses "naked DNA" -- the genetic material of a virus -- has yielded promising results in small animals, Weiner says. "As we get additional study data, we will probably think about trials in larger animals," he says. Human trials are nowhere in sight as yet.

What To Do

Prevention of West Nile virus infection focuses on avoiding the mosquito bites that spread the virus by wearing protective clothing and by eliminating pools of water where mosquitoes can breed.

The CDC has more information on the West Nile virus disease and Japanese encephalitis.

For more information, check out Cornell University.

SOURCES: Interviews with Robert Tesh, M.D., professor of pathology, University of Texas Medical Branch at Galveston; David B. Weiner, Ph.D., associate professor of pathology, University of Pennsylvania, Philadelphia; Nov. 14, 2001 meeting, American Society of Microbiology, Atlanta
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