News update, August 2008

Since we published this report in November/December 2005, avian flu has faded from newspapers, though the pandemic itself still threatens. The number of human cases of bird flu has dropped somewhat in the past two years, but the virus has spread among the poultry of countries like Indonesia, Bangladesh, Vietnam, and Egypt — which has dashed any hope we might have of eradicating the disease entirely. The H5N1 virus is here to stay.

Once the dangers of pandemic avian flu were recognized, medical researchers focused their attention on vaccines that could protect us from the infection. Of particular value would be a vaccine that could be produced in mass quantities ahead of time and stored in preparation for an outbreak. But bird flu, like many other viruses, presents a challenge in this regard. The problem is one of genetic variation. For the reasons described above — the virus’s high mutation rate and ability to trade DNA with other viruses — a huge number of genetically distinct variants of avian flu circulate at any given time. And this can thwart vaccine developers. To work most effectively, a vaccine must be closely matched to the viral strain it is meant to provide protection from. So which of the avian flu strains currently in circulation should be the basis for the vaccine? There’s no surefire way to know which strain will be the first to evolve the ability to jump from human to human — at least not until after the pandemic actually starts. And after that happens, it will likely take several months to produce and begin to distribute the vaccine. That’s the bad news.

The good news involves vaccine adjuvants — substances that can be added to a vaccine to make it more effective. Adjuvants can stretch our vaccine supply, since each person can be protected with a smaller amount of vaccine. And just as importantly, new research suggests that adjuvants may improve the effectiveness of imperfectly matched vaccines against a target virus. This makes stockpiling vaccine ahead of time more practical. Plans are in the works to produce and store 100 million doses of vaccine matched to earlier H5N1 strains — with the hope that this vaccine, perhaps along with an adjuvant, will offer some protection against any avian flu strain that does evolve into a global threat.

News update, July 2009

A few years ago, birds like chickens and ducks seemed poised to spark the next flu pandemic when a deadly strain of avian flu kept popping up in human populations in Asia. Though that killer virus keeps reemerging, in 2009 our fears settled on a different farmyard inhabitant: pigs. For folks in the US, this panic hit closer to home. Since it was first detected in March in Mexico, swine-origin influenza (often called S-OIV or H1N1) has spread to more than 70 countries. Unlike the avian flu, this virus can be passed from person to person, which makes its reach much greater. Fortunately, it is also a milder disease and rarely requires hospitalization.

Recent studies of S-OIV’s evolutionary history have revealed, in surprising detail, how this virus came to be. As described above, many viruses can readily pick-up genes from one another when they infect the same host. An international team of researchers studied the genetic material of virus samples from birds, pigs, and humans — some collected as far back as 1979 — and found that S-OIV is the product of a veritable viral swap-meet. These trades seem to have taken place in pigs, which can be infected by both avian and human flu strains. More than 30 years ago, a Eurasian swine flu virus picked up some genes from an avian virus. Then a different swine virus picked up genes from avian flu and from the usual seasonal flu that affects human populations each winter. Most recently, these two, already mixed-and-matched, swine flu strains joined forces — each contributing genes to the viral strain that would ultimately cause so much fear as it leapfrogged from Mexico to the rest of the world.

This final patchwork virus might have evolved recently — shortly before the Mexico outbreak — or might have been circulating in North American pigs for a decade or more. Since we don’t systematically monitor flu viruses infecting pigs, we simply don’t know.

One thing we can be sure of is that this virus, and others like it, will continue to evolve. By moving livestock (and ourselves!) around the world, we increase the opportunities for distantly related viruses to come into contact with one another and share genes. As they do, the medical and scientific communities will be trying to keep close watch, hoping to prevent the epidemics and pandemics that can be set in motion by such evolutionary leaps.

News update, June 2012

Bird flu is back in the news! But this time, the hullaballoo isn’t over a random outbreak of the deadly disease, but about intentional efforts to create a new strain of H5N1 in a lab. Last year, two groups of scientists announced that they’d produced strains of avian flu that can spread from mammal to mammal — or more specifically, from ferret to ferret, the test organism being used to study the virus. One group of scientists repeatedly passed the virus between ferrets and allowed natural selection to do its work, eventually yielding a virus that could move between animals on its own. When the scientists studied the viral genome, they discovered that just five mutations were responsible for the virus’s new ability! The other group of scientists intentionally combined viral RNA (the flu’s genetic material) from two strains to engineer a ferret-contagious strain of bird flu.

Why would anyone want to make a strain of avian flu that can be passed between ferrets? Obviously, scientists are most worried about human-to-human transmission — but no person would want to volunteer for the role of guinea pig in this experiment! So medical researchers study ferrets. Ferrets are mammals and are on the same branch of the tree of life that humans occupy. Furthermore, the flu causes similar symptoms in humans and ferrets and takes advantage of our cellular machinery in similar ways. Of course, ferrets aren’t humans and no one knows if these new strains of bird flu would be able to spread among humans. Nevertheless, knowing what makes the virus transmissible in ferrets could help us understand viruses in general and, on a more practical level, could help us monitor wild bird flu strains to determine when they are getting dangerously close to human-to-human transmissibility.

While there are many benefits to this knowledge, there is also an obvious risk: the existence of a lethal flu strain that could potentially pass between humans (or could evolve this capability in short order). When the discoveries were first announced, it set some scientists and scientific advisory boards on high alert. Should the scientists who performed the studies be allowed to release their methods and results to the scientific community? This is standard scientific practice and allows others to check the research and build upon it — but what if an aspiring bioterrorist gets a hold of the information? Could he or she use it to trigger a deadly flu pandemic? After many months of debate, watchdog organizations have decided that this is exceedingly unlikely and are allowing the results to be published in full. One study was published last month, and the other is set to appear soon.