The H1N1 flu pandemic last year came out of nowhere. Well, not exactly — H1N1 first emerged in human beings in Mexico. But that wasn’t where most influenza experts were looking. The focus had been on southeast Asia, where the H5N1 avian flu had been infecting — and killing — human beings for the past few years. Most flu pandemics begin in that part of the world, where dense populations of people and animals commingle. H1N1 was different, however, and the world paid the price.
But we may not have learned our lesson. A new study in the June 17 edition of Science makes the case that there has been too little follow-up genetic surveillance of the H1N1 virus — and that we could be vulnerable to new strains. A team of researchers from Hong Kong sequenced viruses found in pigs in the city’s largest slaughterhouse over the past year and a half. They found that the H1N1 virus that had caused a human pandemic last year — and which is still infecting people — had passed back into swine, and was mutating and reassorting with other viruses the pigs had been infected by. (Pigs can be infected by multiple strains of flu viruses, making them living viral mixing bowls.) The researchers worry that H1N1′s mutations could change the virulence of the virus. Although there’s no evidence that has happened, there have always been concerns that H1N1 might mix with H5N1 to produce a new virus that has the transmissability of the former — H1N1 has reached 200 counties and is still infecting people — and the severity of the latter, which has an observed mortality rate of nearly 60%.
We can’t stop flu viruses from intermingling — that’s just what they do. But we can try to keep close track of new viruses through genetic surveillance — just like the kind practiced by the researchers in Hong Kong, who’ve been testing the city’s pigs for viruses as part of a 12-year-old U.S.-funded program. While major hog producers in the U.S. and Europe frequently test their pigs for flu viruses — which helps scientists keep track of what’s going on among swine — that’s rare among smaller producers in Asia, even though that’s exactly where pandemics often begin. The Science study underscores the need for better surveillance in the developing world:
“The message from our paper is not an inevitable disaster around the corner, but the need for continued vigilance,” Malik Peiris, a flu expert at the University of Hong Kong and one of the study’s authors, said in an e-mail message.
We were lucky with the H1N1 pandemic, which turned out to be relatively mild. So mild, in fact, that some have accused the World Health Organization of overhyping the virus. A damning recent report in British Medical Journal found that World Health Organization (WHO) advisors who called for the stockpiling of H1N1 vaccine had been previously on the payroll of the drug companies that made the vaccines. (The WHO has said that there is no evidence to show that it engaged in scaremongering during the pandemic.) But that’s the thing about the flu — you never know when your luck will run out.