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Genes Found That Make Hepatitis A Virulent

Scientists also discover weakened virus can revert to its infectious form

TUESDAY, Aug. 13, 2002 (HealthDayNews) -- The genes that make hepatitis A (HAV) virulent have been located by researchers at the National Institute of Allergy and Infectious Diseases (NIAID).

The scientists also discovered that HAV that's deliberately weakened is able to quickly revert to its natural infectious form. That means it could be difficult to create an improved type of vaccine against HAV.

The findings will be published in the Sept. 1 issue of the Journal of Virology.

"As sanitation improves in developing countries, there will be an increased need for inexpensive and easy-to-administer vaccines to prevent hepatitis A, which is transmitted through contaminated food and water," says lead researcher Suzanne Emerson.

Almost all people in developing countries become infected with HAV during childhood and thereafter are immune to HAV. But improvements to water quality and sanitation mean that naturally acquired immunity may not occur as often.

People who become infected with HAV for the first time later in life are more likely to suffer serious illness and severe liver damage.

While there is a vaccine made from killed HAV, it has to be administered in multiple booster shots. The expense and inconvenience of that vaccine restricts its use in developing countries.

The NIAID researchers want to develop a single-dose, oral vaccine made with a weakened form of the HAV virus.

The first step was identifying the genes that make HAV virulent. The researchers did that. The two genes are called 2C and VP1/2A.

The NIAID researchers then altered those two genes to weaken HAV. They believed that would be the way to produce a vaccine. But when they injected the weakened HAV into monkeys, the virus mutated in the monkeys.

The monkeys didn't actually develop any disease, but their feces had infectious particles that could cause HAV in other monkeys.

"Although these results suggest that a live, attenuated HAV vaccine may be difficult to develop, they do help us better understand what controls HAV growth. Ultimately, this knowledge may provide us with a roadmap to a less expensive and more potent killed vaccine that could be used worldwide," Emerson says.

More information

The Centers for Disease Control and Prevention offers this fact sheet on hepatitis A.

SOURCE: National Institute of Allergy and Infectious Diseases, news release, Aug. 8, 2002
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