2006年VOA标准英语-Scientists May Have Vaccine for Deadly Las（在线收听）

By Zulima Palacio
Washington, DC
03 February 2006
 
watch Lassa report

When it comes to dangerous jobs, we usually think of things like racing cars, testing explosives or exploring space.  Actually, one of the most dangerous jobs is in a type of laboratory known as "biosafety level four".  That is where scientists research unknown and deadly viruses, including Lassa fever. It can be fatal, is endemic in West Africa, and is on the U.S. list of potential bioterrorism weapons.  Amy Katz narrates the report.

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Researcher working in lab  
  

Researching and testing a virus that has no cure requires extreme precautions.  In San Antonio, Texas is one of the most secure laboratories in the U.S: a “safety level four” facility.   There are only a few of them and they are expensive and complex to operate. The most dangerous viruses associated with bio terrorism, such as Ebola, Anthrax, and Lassa fever, have been studied here.   Any animals used in tests must be euthanized and cremated to avoid accidental release of viruses. 

Dr. Jean Patterson is the Chair of the Department of Virology and Immunology here at the Southwest Foundation for Biomedical Research.

"Safety level four is a type of laboratory where you work with things for which there is no vaccine, no treatment, is potentially lethal and can be transmitted in the lab."

"The procedure for dressing up and going in takes about 30 minutes,” says Dr. Ricardo Carrion, a staff scientist at the Virology Department. “By the time you put your suit on, and check to make sure there are no holes in it, and enter, is a rather long period.  Once you get in there, it takes another 20-30 minutes to come out.  It takes about seven minutes to leave the laboratory but then you have to take a physical shower and get dressed.  So basically once you are in there you want to stay in there until you are done with your experiments."

Dr. Carrion explains that in order to avoid doing that constantly, they use surveillance cameras to watch what's going on in the lab.

"Instead of going in four times a day, we're able to look at the animals directly to see how they're doing."

These guinea pigs are being use to test a potential vaccine for Lassa fever, not a common illness in most places, but endemic in West Africa, where every year it affects between 300,000 and 500,000 people.  A rodent immune to the virus transmits it.  Lassa fever is often misdiagnosed and mistreated.  Most of the time the human immune system can deal with it.  But if it develops into hemorrhagic fever, it can be deadly.

"About 15 percent of those that get hemorrhagic fever end up dying, whereas with women, if they are infected and they are pregnant, it is about 60 percent," says Dr. Carrion.

So far, the test of the vaccines originally developed by the University of Maryland, but never before tested, is showing promising results. According to Dr. Carrion, animals are given the vaccine and then infected with the Lassa fever virus.

"We took this virus and we vaccinated guinea pigs and 30 days after we vaccinated them we challenge them with a lethal dose of Lassa virus, actually 1,000 times what would take to require to make an animal sick. And we found that these animals, not only didn't get sick, but in their tissue level there was no damage. We look at enzyme levels, that indicate liver damage, we didn't see any of those in the blood stream throughout the infection"

Once the studies with guinea pigs are finished, they will move on to monkeys.  If and when the vaccine proves to be safe and effective in monkeys, there will be human trials, says Dr. Patterson. 

"Assuming we can make it work in a primate, non-human model and we can get a license from a large pharmaceutical company, I would say in five years, when it could start being put into humans," she said.

West Africa could be the first beneficiary of the vaccine.  But the U.S. government, which is financing the research, also wants to maintain a reserve in case of a bio-terror attack using the Lassa virus.  If everything goes well, scientists at the Southwest Foundation eventually plan to produce a dual vaccine for yellow fever and Lassa fever.