At an informal meeting Dr. Bernard Vallat presented an overview on current and future activities of the organisation while addressing the need for global animal health strategies to control emerging and re-emerging infectious animal diseases worldwide.

In this context, the issue of highly pathogenic avian influenza and the current situation with H5N1 was raised by some of the reporters.

Dr Vallat said – as he has said in the past – that although the H5N1 virus is extremely virulent, it has shown to be quite stable over the last few years and its epidemiological behaviour remained the same from the beginning of the crisis in 2003. He added that this observed stable behaviour of the H5N1 strain of the virus does not allow ruling out the risk of a mutation into a new dangerous form for humans, thus becoming a potential candidate for an avian influenza pandemic.

Dr Vallat also said that while no one can predict when and how a human influenza pandemic will occur, this may not originate from the highly pathogenic avian influenza H5N1 South East Asian strain which is only one of many other influenza virus strains that can eventually be responsible for a pandemic.

“Bird flu will always remain a risk, be it H5N1 or another and for that reason pandemic preparedness as well as permanent control of the pathogen at the animal source are important”, he said.

In other interviews, experts such as Dr. Kathy Neuzil, MD, chair of the Infectious Diseases Society of America's (IDSA's) Pandemic Influenza Task Force, countered that the virus has been known to mutate many times already and that both science and history suggest it still represents a very real threat. According to CIDRAP, accounts from the Associated Press (AP), Agence France-Presse (AFP), and Reuters offered somewhat different versions of Vallat's comments, with the AP making him sound the most reassuring—or complacent.

According to the AP, Vallat said, "The risk [of a pandemic] was overestimated." Concern a few years ago about a possibly imminent pandemic represented "just nonscientific supposition," he said.

An AFP account focused on Vallat's statements about the stability of the H5N1 virus. "We have never seen a virus which has been so stable for so long," Vallat was quoted as saying. "Compared to other viruses, it is extremely stable, which minimizes the risk of mutation" into a pandemic strain.

He also said the virus is endemic in Indonesia, Egypt, and to a lesser extent Nigeria, according to AFP. "If we could eradicate the virus in those countries, the problem of a pandemic from Asian H5N1 would be resolved," he asserted.

But the Reuters report depicted Vallat as more cautious. "We notice that the virus is now extremely stable but there is no base to say that the H5N1 will not mutate," he said. "Bird flu will always remain a risk, be it H5N1 or another."

Despite the somewhat conflicting accounts, the other experts asserted that Vallat was sending the wrong signal.

"The main message that should be out there is that the threat is real," said Neuzil, senior clinical advisor with the nonprofit organization PATH in Seattle.

She and others pointed to the recent history of pandemics.

"The 1918 pandemic occurred from a mutation of a bird virus, to the best of our knowledge," she said. "The 1957 and 1968 pandemics occurred through viral reassortment, sudden events where human and animal viruses combined genes and came out with a new virus. So a pandemic can occur either way. You can have a very stable virus that reassorts with another virus."

"H5N1 has a demonstrated ability to mutate and change," she added. "We've seen it change in Vietnam, where in the course of a week or two in patients on [antiviral] therapy it has developed resistance." Mutations also have been seen in Indonesia, she noted.

"If you just stick to the science, science tell us pandemic threats are real, and there's nothing to say that H5N1 couldn't cause a pandemic by either of those routes [mutation or reassortment]," she concluded.

David Halvorson, DVM, a veterinary pathologist and avian flu expert at the University of Minnesota in St. Paul, said he was hesitant to respond to Vallat's comments, given the differing accounts of what he said. However, Halvorson allowed, "People have noted that the Asian lineage highly pathogenic H5N1 has been around since 1997 and nothing has happened yet to cause it to spread from human to human. Does that mean it couldn't happen tomorrow? No."

David Fedson, MD, a retired professor of medicine from the University of Virginia and former researcher with Aventis Pasteur who has spent his career working on vaccination issues, agreed with Neuzil that Vallat's assessment doesn't fit with history.

"The statement [suggesting the risk of a pandemic is minimal] ignores history," said Fedson, who also is on the IDSA's Pandemic Influenza Task Force. "The history is a pandemic coming out of nowhere in 1918 and causing great global disruption. . . . A statement like this, if people pay attention, has the practical effect of telling people they don't need to worry, they don't need to be prepared."

Fedson said infectious diseases have caused major die-offs in several mammalian species in recent years, and humans are subject to the same threats. For example, about a third of the lions on Africa's Serengeti Plain died of distemper virus in the early 1990s, and more than 50% of gorillas and chimpanzees have died of Ebola virus infection in this decade, he said.

"Given what we know of the capability of flu viruses in general and this virus in particular, we have to take it seriously and . . . prepare for a pandemic that could cause a very high mortality," Fedson said. "We have to recognize that we're as vulnerable as the gorillas and chimps."

Infectious disease expert Michael T. Osterholm, PhD, MPH, a leading pandemic preparedness proponent, recommended viewing the reports of Vallat's comments with caution because of their differences. Nonetheless, he took strong exception to the idea that the virus is stable and doesn't represent much of a threat.

"Regardless of what Dr. Vallat said, this virus is hardly stable," said Osterholm, director of the University of Minnesota Center for Infectious Disease Research and Policy, publisher of CIDRAP News. With multiple clades and subclades of the virus identified, he said, "This virus has demonstrated an unprecedented ability to change through mutation."

He said the virus is stable only in the sense that it seems to have found a permanent home in poultry and wild birds. "There is nothing in the foreseeable future to suggest that this virus is going to die out or somehow disappear through competition or attrition in the bird reservoir," he added.

As for history lessons, Osterholm cited the flu virus subtype H3N8. Originally an avian virus, it jumped in 1960 to horses and circulated in them for decades, he said. About 5 years ago it jumped from horses to dogs, and it continues to circulate in dogs in a number of areas worldwide.

"Why did it take nearly 40 years of nearly constant contact between horses and dogs before it finally made the jump to dogs?" Osterholm asked. "No one can answer that question. That should provide a rather sobering context to understanding H5N1. Three or 5 or 7 years of hypertransmission in the bird population doesn't really tell us anything about whether this could one day become a pandemic strain."

Osterholm concluded, "Unfortunately, some have read this [Vallat's comments] to mean that the final chapter has been written on our concern about pandemic flu. There's nothing that could be further from the truth. We're closer today to the onset of the next pandemic than we were yesterday, but not as close as we'll be tomorrow."

Further Reading

- You can visit the Avian Flu page by clicking here.