Pigs at the Granjas Carroll de Mexico pig farm in Perote, Veracruz, Mexico
Given the speed with which the H1N1 flu virus spread around the world — and the relentlessness with which it has been tracked by the media — it can be hard to believe that less than two weeks have passed since the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) first responded to reports of an unusual respiratory illness.
But even in Mexico City, the epicenter of the global H1N1 outbreak — as of May 4, the WHO had confirmed more than 1,000 cases in 21 countries — the disease seems to be slowing down. The government announced on Monday that restaurants in the capital city would reopen by May 6, with churches and museums following soon afterward. In the U.S., where the CDC has confirmed 286 cases of H1N1 in nearly every state, health officials noted that the illness remained mild. Still, officials point out the need to maintain strict surveillance for new cases, in the U.S. and especially in countries in the southern hemisphere, where flu season is about to begin. (See the top five swine flu don'ts.)
"While we're not out of the woods, we are seeing some encouraging signs," says CDC acting director Richard Besser.
As the global panic subsides, scientists will focus on figuring out how to ward off the next emerging disease before it lands on our doorstep. "Now is the time to take the actions needed to prevent this," says Nathan Wolfe, director of the Global Viral Forecasting Initiative, which looks for new pathogens emerging from wildlife. One way to start would be to trace how, when and where the H1N1 virus emerged from pigs into people (or vice versa — over the weekend, Canada confirmed reports that a swine worker in Alberta passed the H1N1 virus to pigs). The H1N1 virus contains human, avian and swine flu genes, and genetic analysis indicates that it reassorted years ago, meaning it could have been in pig populations for some time before the virus gained the ability to transmit easily from person to person. If we had had tight surveillance of flu infections among swine, we might have noticed that something bad was brewing. (See pictures of thermal scanners hunting for swine flu.)
But we don't — unlike diseases like foot and mouth, swine flu is not an infection that is automatically reported to national health authorities. Flu is common among pigs but not much more deadly than it usually is among people. (The H5N1 bird flu virus, by comparison, destroys poultry populations.) That means that flu infections in swine herds can easily fall under the radar, as seems to have been the case with the new H1N1. Though there were sporadic reports of flu infections passing from pigs to people over the past few years, "we hadn't seen anything that tipped us off that this was something different," says Tom Burkgren, executive director of the American Association of Swine Veterinarians.
A team of scientists from the Food and Agriculture Organization (FAO), the World Organization for Animal Health and the Mexican government is now beginning an investigation in Mexico, taking blood samples and swabbing the inside of pigs' nostrils, looking for H1N1 infection. The hope is to find out how prevalent the virus is among Mexican pigs — if at all — and begin to trace back the virus.
It won't be easy. It took years to find the original animal sources of SARS and HIV, among other new diseases. What makes tracking emerging viruses inside wildlife populations all the more difficult is that animals — even more than people — move around a lot, across borders. The U.S. imports live pigs from Europe, while Mexico takes in some 600,000 pigs a year from the U.S., so it's entirely possible that the virus began in Europe (the H1N1 virus has Eurasian genes), then moved to America and Mexico with pigs before infecting the first human. "It's going to take several weeks and maybe months to get a clearer picture," says Juan Lubroth, a senior officer at the FAO. "There's just a lot that we don't know." (Read "Swine Flu: Don't Blame the Pig.")
Although it is too late to put the H1N1 virus back in the bottle, there are lessons to be learned for containing future pandemics. One is the need to improve monitoring of the trade in live animals, which can spread new diseases across borders and even oceans. Peter Daszak, president of the Wildlife Trust, notes in a newly published paper in Science that the U.S. alone has imported more than 1.5 billion live animals since 2000, the majority of which undergo no testing for pathogens before or after shipment. At the height of the H1N1 scare last week, many Americans wanted stronger surveillance at the borders to prevent the spread of new diseases by foreign travelers — but there has been comparatively little attention paid to the live-wildlife trade. "There's a backdoor open just waiting for new pathogens to walk in," says Daszak.
In the U.S. and around the world, veterinary health care is the poor cousin to human health, chronically underfunded. But if we are serious about heading off new infections, we need to increase available resources and make sure that veterinarians are looking out for new diseases in livestock and wildlife in the same way that the WHO's global flu network is constantly monitoring the world's human population for new influenza strains. As we've seen with H1N1, once a new flu has emerged and begun spreading among people, it's likely too late to contain. "What we need to do is upstream surveillance in animals and wildlife," says William Karesh, vice president of the Wildlife Conservation Society's Global Health Program. "We've begun to do that with avian flu, but the funding isn't available for other species."
In case we had any doubts, the rapid spread of the H1N1 virus should convince us that biologically, we live in one world, sharing microbes between species and across borders. When it comes to crafting a global early-warning system equal to the challenges posed by new pathogens, we're only as strong as our weakest link, whether that's the lack of animal-disease surveillance in the U.S. or the less-than-ideal laboratory capacity in Mexico. "We have to break down the barriers between organizations and agencies," says Lubroth. "It's one world, one health."