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See Inside July 2009

Could Animal Surveillance Have Seen Swine Flu Coming?

The surveillance of animals for new flu viruses has lagged behind preparations for the human pandemics that can be caused by the bugs
pig in peru



Credit: Geraint Rowland via Flickr

Less than 24 hours after a commercial jet took a sudden detour into the Hudson River this past January, security camera video of the event from multiple vantage points began surfacing. In an age of ubiquitous surveillance, the public has come to assume that someone or something is always watching, ready to spot trouble as it is happening. Yet a novel strain of the influenza A (H1N1) virus jumped species and burst into the human population in March and April, and by late May health and agriculture officials were still trying to figure out where it came from.

The emergence of the new H1N1 flu strain has demonstrated the effectiveness of existing systems to watch for human flu outbreaks while also proving a long-standing theory that pigs could serve as mixing vessels for a pandemic virus. But it has also highlighted how disappointing progress has been in detecting where and how such viruses evolve in animals and in predicting their transmission to people—abilities that might have helped avert a pandemic or at least provide an early warning.

Despite years of attention and funding for flu research, however, health officials are no closer to having an efficient way to flag new animal pathogens that could harm people. For example, in 2007, when Jürgen A. Richt and his colleagues at the U.S. Department of Agriculture’s National Animal Disease Center in Ames, Iowa, identified a new influenza A (H2N3) strain in pigs that they thought had pandemic potential, “there was no one to tell,” he recalls. “So we asked ourselves, ‘What do we do with it?’ Nobody was interested—there was no rule or regulation in place.” Richt and a group of collaborators published their assessment of the new strain in a scientific journal article that concluded that “it would be prudent to establish vigilant surveillance in pigs and in workers who have occupational exposure.”

In the context of disease, surveillance means at a minimum that doctors and diagnostic laboratories report every instance of certain pathogens they detect. All human flu cases are “reportable” to the Centers for Disease Control and Prevention, for example, which tracks the incidence and movement of the illness. But for both people and animals, voluntary lab testing to diagnose flu captures only the small fraction of cases that ever involve a doctor visit. Systematic sampling and mandatory reporting of disease in swine herds are limited to a handful of commercially devastating illnesses, including classical swine fever and nipah virus.

Richt, now at Kansas State University, thinks veterinary diagnostic labs could play an important role in more active animal screening by testing every sample submitted for any reason for a full spectrum of pathogens. “We need a better network to look in animal populations for emerging infectious agents, with 21st-century technology,” he says. Big state laboratories, including the ones in Iowa and North Carolina, home to the largest U.S. swine populations, already have the technical ability to screen for a range of pig diseases, Richt explains. Microarray chips able to test for pathogens specific to pigs, cattle or poultry could give smaller labs the same capacity and provide a more comprehensive, real-time picture of microbial threats to people, such as a new flu variant, brewing in livestock.

Identifying novel flu strains in animals is one thing; determining whether they pose a human danger is another. “I’m a lot more pessimistic about being able to predict these things,” says Jeffery K. Taubenberger of the National Institute of Allergy and Infectious Diseases. In March he published an analysis of two swine branches of the H1N1 family tree—one of them a Eurasian strain that contributed segments of the novel H1N1 now infecting humans. The two strains had a common H1N1-type ancestor, but both have been evolving independently in pig populations, and the minute changes to viral genes that allowed the virus to adapt to a new host were different in each strain. Many other scientists looking for consistent signals that a virus is changing hosts or is becoming more transmissible or more virulent have also failed to find clear patterns.

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