Scientists test bird flu's potency
Updated: 2004-02-25 11:25
Scientists are embarking on a series of experiments with the bird flu virus ravaging Asian poultry to see how dangerous it would be if it adapted to humans, the chief influenza expert at the U.N. health agency said Tuesday.
Researchers will mix the virus with a human flu variety to see how well they swap genes and test various combinations on ferrets and other animals to determine which would be the most hazardous, said Klaus Stohr, chief flu expert at the World Health Organization, which is coordinating the tests.
What we want to do is reduce surprises. Every surprise will cost lives," Stohr said in Geneva. "We still have the time here to do the research. We don't have much time, but the pandemic isn't there yet."
The avian influenza outbreak has forced the slaughter of more than 80 million chickens and other fowl in Asia, but human infections remain rare.
Experts agree it is only a matter of time before a deadly human flu pandemic develops, and most suspect the current bird flu strain is the most likely candidate to cause it.
"It's not a virus which we have been able to get rid of. It comes back, comes back and these outbreaks are getting bigger and bigger," Stohr said. "This is the virus which everyone would bet their money on."
There are two ways the bird flu virus sweeping Asia could become a serious danger to humans.
In one, it could accumulate enough genetic mutations on its own to become good at passing between humans. Experts are tracking the virus to detect any significant genetic changes, but so far none has been recorded.
The more scary possibility would be a sudden change in the virus, brought on by combining with a human flu strain in someone's body. The two viruses could swap genes and create a potent hybrid with the deadliness of the bird strain and the contagiousness of a regular human strain. It only takes one person with a double infection to set off such a chain of events, Stohr said.
Studies in monkeys using only pure bird flu virus will be conducted in Rotterdam, the Netherlands, at the same laboratory where key experiments involving the SARS virus were carried out, Stohr said. Results are expected by the end of March. The locations for laboratory studies and experiments on other animals have not yet been announced.
Studying how the pure bird flu virus behaves in monkeys is considered a good indicator of how a pandemic strain based on the virus could behave in humans.
The experiments in Rotterdam are expected to answer many mysteries about how the virus might behave in humans, such as the incubation period, how long people remain infectious, when antibodies are detectable, when fever starts and subsides, how likely survival would be and whether the virus could be spread through urine or feces as well as saliva. The tests will also help authorities determine whether it makes sense to close schools and restrict travel.
Autopsies will be conducted on the infected monkeys to try to determine the best treatment for the virus.
"We don't know whether this virus is spreading in the entire body or whether it's just in the lungs," Stohr said, noting that information is key to deciding which of two available drugs to use to treat it.
"Tamiflu reaches therapeutic levels in many tissues. Relenza does not. It is only in the lung," he said. "If this virus gets into the brain, the liver and other parts of the body, then Relenza would be out. We could only use Tamiflu."
"All these questions cannot be answered without doing the proper trials now," he added.
Laboratory studies, which are expected to start by the end of March, aim to understand how likely the bird flu virus is to mate with a human flu variety.
Some of the tests will involve placing the two strains together in bottles to see how easily they mix and to track which genetic reshuffles occur most frequently. Each virus has only eight genes, making the number of combinations manageable to study.
The tests will give clues to what kind of reshuffling is most likely to occur if a pandemic strain does emerge. Experts would then be able to distinguish between dangerous combinations and benign ones and respond accordingly.
The next step would be to inject the new hybrid into animals to see how it behaves. Ferrets would be used first, then perhaps monkeys.
"We are getting ammunition," Stohr said of the experiments. "We don't want to go into battle without having a reconnaissance mission. We don't want to go into a pandemic without knowing what the enemy is, and that's what this is all about."
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