It’s Back: Bird Flu Returns, and This Time It’s Mutated

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During the last couple of flu seasons, we were all worried about H1N1, a new and virulent strain of influenza, but this winter we may have to contend with a much deadlier foe: H5N1, or bird flu. Some Asian countries are reporting this week the first cases of a mutant strain of the virus spreading in poultry.

The U.N. Food and Agriculture Organization (FAO) reported on Monday that the H5N1 virus has mutated, something that public health officials had feared would happen and that could possibly make the virus more dangerous to people.

In its original form, H5N1 primarily infects wild birds and poultry, including geese, chickens, ducks and turkeys, but only rarely jumps into people. Still, the fact that some people have become infected with H5N1 by eating improperly prepared and contaminated poultry — the virus has killed 331 people and infected 565 since it first appeared in 2003 — led experts to warn that it was only a matter of time before it altered into a form that made it easier to spread to humans.

It’s not clear yet whether that has happened, but health authorities are concerned by the an new H5N1 variant spreading in poultry in both China and Vietnam; the new strain is resistant to current vaccines. In the years since H5N1 began spreading among bird and poultry flocks, millions of birds have been culled, and many countries have adopted vaccination programs to inoculate domestic fowl to prevent the spread of the virus. But six countries have continued to see H5N1 among their poultry population each year: Bangladesh, China, Egypt, India, Indonesia and Vietnam.

And after declining since a peak in cases in 2005-06, when some 4,000 cases were reported, the rate of H5N1 outbreaks among both animals and people has started to inch up this year. “When you look at 2011, there is a trend upward in cases,” says Juan Lubroth, FAO’s chief veterinary officer. “And in several countries that had experience with H5N1 already, they are seeing a new introduction of [the virus]. We want to alert the community that we are seeing an upswing of cases.”

Already, Cambodia, which shares a border with Vietnam, has reported eight cases of H5N1 infection this year, and all have been fatal. It’s not clear whether any of these involved the mutant strain, but experts say the more cases of infection among humans and birds there are, the more opportunities the virus has to recombine and mutate into a form that is more easily transmissible to people.

Containing the new H5N1 strain, known as H5N1, may be a challenge, since many of the infected fowl are wild species that migrate, and can easily spread the virus over thousands of miles. In the past two years, experts have tracked the original version of H5N1 to regions where it has never been reported before. It has also shown up again in places that had been virus-free for several years, including Israel, the Palestinian territories, Bulgaria, Romania, Nepal and Mongolia.

The same could happen with H5N1 “What has surprised us a bit is the geographical spread and also some concerns that the vaccine readily used in combating H5N1 is not as effective with this particular strain,” says Lubroth. “There is a concern there, so we wanted to alert the world community.”

But as alarming as the appearance of the mutant, vaccine-resistant strain is, some experts say that it’s not that surprising. Unlike the vaccines we use against human flu, influenza inoculations for poultry don’t change year to year, so it was just a matter of time before a resistant strain would emerge.

Most agriculture experts continue to use the same vaccine for 10 to 20 years with reasonable success in containing influenza in their flocks. “The reason the vaccine is now not working well is that the [Vietnamese] eventually pushed their luck too far,” says Ruben Donis, chief of the molecular virology and vaccines branch in the influenza division of the U.S. Centers for Disease Control and Prevention (CDC). “They have been using the same vaccine from 1996, so the virus in the vaccine is 15 years old.”

Lubroth says that Chinese health authorities are currently working on a new vaccine that could block the mutant influenza strain more effectively, and that FAO is discussing with Vietnamese authorities how best to proceed with their poultry vaccination in light of the appearance of the new virus. Continuing to inoculate poultry with an ineffective vaccine would only push the virus to mutate more rapidly toward a resistant and possibly more virulent strain.

Health authorities aren’t sure how the new strain will impact the upcoming human flu season, but they aren’t taking any chances. When the World Health Organization’s influenza experts met in February to decide which strains to include in the upcoming seasonal flu shot, they also selected certain virus strains to be stockpiled in case of an outbreak. One of those was a version of H5N1 of the same clade, or group, as the mutant strain now circulating among the birds in China and Vietnam. That means that the virus is ready to go for testing and development into a vaccine should it suddenly emerge as a problem among people.

And such preparedness is critical when it comes to the notoriously unpredictable flu. In an earlier statement on FAO’s website, Lubroth noted, “The general departure from the progressive decline [in H5N1 cases] observed in 2004-2008 could mean that there will be a flare up of H5N1 this fall and winter, with people unexpectedly finding the virus in their backyard. Preparedness and surveillance remain essential. This is no time for complacency. No one can let their guard down with H5N1.”