Jan 14, 2004 (CIDRAP News) – One of the worst fears of infectious disease experts is that the H5N1 avian influenza virus now circulating in parts of Asia will combine with a human-adapted flu virus to create a deadly new flu virus that could spread around the world.
That could happen, scientists predict, if someone who is already infected with an ordinary flu virus contracts the avian virus at the same time. The avian virus has already caused at least 48 confirmed human illness cases in Asia, of which 35 have been fatal. The virus has shown little ability to spread from person to person, but the fear is that a hybrid could combine the killing power of the avian virus with the transmissibility of human flu viruses.
Now, rather than waiting to see if nature spawns such a hybrid, US scientists are planning to try to breed one themselves—in the name of preparedness.
The Centers for Disease Control and Prevention (CDC) will soon launch experiments designed to combine the H5N1 virus and human flu viruses and then see how the resulting hybrids affect animals. The goal is to assess the chances that such a "reassortant" virus will emerge and how dangerous it might be.
CDC officials confirmed the plans for the research as described recently in media reports, particularly in a Canadian Press (CP) story.
Two ways to make hybrids
The plans call for trying two methods to create hybrid viruses, CDC spokesman David Daigle told CIDRAP News via e-mail. One is to infect cells in a laboratory tissue culture with H5N1 and human flu viruses at the same time and then watch to see if they mix. For the human virus, investigators will use A (H3N2), the strain that has caused most human flu cases in recent years, according to the CP report.
The other method is reverse genetics—assembling a new virus with sets of genes from the H5N1 and H3N2 viruses. Reverse genetics has already been used to create H5N1 candidate vaccines in several laboratories, according to Daigle. The National Institutes of Health (NIH) said recently it would soon launch a clinical trial of one of those vaccines.
Of the two methods, the co-infection approach was described as slower and more laborious, though closer to what happens in nature.
Any viable viruses that emerge from these processes will be seeded into animals that are considered good models for testing how flu viruses behave in humans, according to Daigle. The aim will be to observe whether the animals get sick and whether infected animals can infect others.
The World Health Organization (WHO) has been "pleading" for laboratories to do this research, because it could provide some evidence to back up the agency's warnings about the risk of a flu pandemic, according to the CP report.
Klaus Stohr, head of the WHO's global influenza program, was quoted as saying that if none of the hybrids caused disease, the agency might be inclined to dial down its level of concern. But if the experiments produce highly transmissible and pathogenic viruses, the agency will be more worried, he said.
Safety precautions
Because of the obvious risks in creating viruses with the potential to spark a pandemic, the work will be done in a biosafety level 3 (BSL-3) laboratory at the CDC in Atlanta, Daigle told CIDRAP News.
http://www.cidrap.umn.edu/cidrap/content/influenza/panflu/news/jan1404hybrids.html
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