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TUESDAY, Aug. 12, 2003 (HealthDayNews) -- A close but relatively toothless Australian cousin of West Nile virus could potentially be a vaccine against the deadly mosquito-borne infection that has struck in 20 U.S. states so far this year.
Mice vaccinated with a weakened strain of the microbe, called the Kunjin virus, don't contract West Nile even when injected with lethal amounts of the pathogen, Australian researchers say. Kunjin is endemic to Northern Australia, and while it can also infect people, it rarely sickens them.
"The unique aspects of this West Nile vaccine are its relative safety -- we start with a well-characterized, naturally attenuated virus and further attenuate it -- and its stability," says Roy Hall, a microbiologist at the University of Queensland in Brisbane, and the leader of the research effort.
The DNA-based vaccine can be stored at room temperature without losing its protective powers, unlike live-virus inoculations that must be kept frozen to remain viable, he adds.
Widespread Kunjin activity in Northern Australia might help explain why that continent has seen no cases of transmitted West Nile so far, Hall says. An infected racehorse from North America was imported to the country, but it did not appear to serve as a reservoir for additional infections.
"Probably the next step will be to test it in horses, where there is also a demand for a safe, effective vaccine," says Hall, whose study appears this week in the Proceedings of the National Academy of Sciences. "Humans will be farther down [the] track."
As of Tuesday, the U.S. Centers for Disease Control and Prevention had received reports of 367 cases of West Nile in 20 states, including nine deaths in three states.
U.S. health officials reported last week that the number of human West Nile infections tripled in the preceding week, which they warn could mean more people stricken with the disease this year than ever before.
Last year, 4,156 people in the United States developed confirmed West Nile infections and 284 died of the disease, according to the CDC. Those figures were by far the highest annual caseloads since the virus appeared in this country in 1999. Experts believe only one in 100 infected people develop symptoms.
Most people who are infected with the virus will not develop any symptoms. The risk of severe illness and death is highest for people over 50 years old.
Scientists have been pushing hard for a West Nile vaccine, though none is commercially available yet. Researchers in Israel, which also has had a problem with the infection, have shown that geese can be protected from West Nile by injecting them with inactivated strains of the organism as well as a related flavivirus.
Dr. W. Ian Lipkin, a West Nile expert at Columbia University in New York City, calls the new results from Australia "significant. Although studies in mice do not always translate to humans, this advance is likely to add to the armamentarium of candidate vaccines for prevention of West Nile virus-associated disease."
Using one virus to build immunity against another has a strong pedigree. In 1796, the English country doctor Edward Jenner gave birth to modern immunology when he discovered that infecting people with cowpox protected them against its lethal cousin, smallpox. The word vaccination comes from the Latin for cow, vacca.
More information
For the latest on West Nile, check out the Centers for Disease Control and Prevention or the National Institutes of Health. For a history of Edward Jenner's pioneering work with smallpox, check out this site from the University of South Carolina.
