Sick? Don’t blame the pig
It looked like an open-and-shut case.
More than half the genes in the H1N1 virus behind the current flu outbreaks were traced to pigs. The first person known to be sickened with swine flu in Mexico, the outbreak’s epicenter, lived near an industrial farm that produces almost a million hogs a year.
The virus was quickly dubbed “swine flu.”
Officials in Egypt ordered destruction of all 300,000 of the country’s pigs. Afghanistan’s one known pig was quarantined. Pork imports were banned by some nations due to unfounded fears that the virus might linger in cooked meat.
But don’t turn the pig into a scapegoat.
“The easy way out is to blame the pig,” said Robert Webster, a virologist at St. Jude Children’s Research Hospital in Memphis, Tenn., and a preeminent expert on influenza.
Though pigs provided a share of the raw material, he and others said, the viral bomb probably couldn’t have been assembled without a small cadre of jet-setting humans carrying flu viruses across oceans, unwittingly mixing and matching them -- perhaps inside their own bodies.
“This is a human virus,” Webster said.
Indeed, the flu strain, which has killed dozens of people and sickened thousands more since March, has yet to be found in a single pig outside Alberta, Canada, where an infected farmworker -- yes, a person -- transmitted it to a herd.
Pigs do harbor flu viruses, and sometimes we catch them. But next to regular flu, which infects as many as a fifth of the people in the U.S. each winter, swine flu in people is rare. Virologists have documented about 50 cases in the last 35 years.
It is also true that swine influenzas can contribute portions of their genomes to the starkly new flus that rise up at times to plague us. An unusual class of flu that combines pig, avian and human viruses jumped to people 12 times between December 2005 and February 2009, according to a report released Wednesday.
One of those strains is an ancestor of the new H1N1 flu, though there are significant differences in a key gene, H1.
“Do pigs contribute to the flu gene pool? Yeah, and so do people and so do wild birds,” said Dr. Kurt Rossow of the University of Minnesota, who studies diseases in people who handle pigs. “I just don’t agree that pigs are an evil mixing vessel just boiling over with flu that’s pumping out to people on a regular basis.”
If accusing fingers have pointed at pigs, they have also pointed at modern-day pig-farming practices.
Such operations are part of a global industry that bears little resemblance to the “Charlotte’s Web"-style sties of yesteryear. Most pigs are raised indoors, thousands under one roof. The ground is concrete or a synthetic material; urine and excrement fall through slats.
It’s a crowded, unnatural environment that can spur creation of new viruses, critics say.
“When you concentrate animals, you both stress their immune systems and create conditions where microbes can become more virulent more quickly, which is exactly what you don’t want leaking into the human population,” said Dr. David Wallinga, director of the Food and Health Program at the nonprofit Institute for Agriculture and Trade Policy.
He said he didn’t know of any studies that prove this, “but when I talk to farmers, they will say that when pigs are raised on pastures or in barns, they just don’t get sick.”
Animal scientists say that is not so. The biologically secure facilities, they say, protect pigs from germs like flu. The air is filtered, and bacteria-rich animal waste is kept out of pens. There is virtually no exposure to wild birds or other animals.
The number of humans who come into contact with the animals is far lower than on traditional farms, reducing risk of infection either way. People entering the facilities must shower and change into special clothes. “You don’t even wear your own underwear in these facilities,” said Dr. Liz Wagstrom, a veterinarian and officer of the National Pork Board.
The new H1N1 is a transcontinental combination of flu segments from North America, Europe and Asia. Virologist Jan de Jong of the Netherlands’ National Influenza Center said that based on genetic analysis, the last step in the mix-and-match process probably occurred late last year.
He said he was surprised, in these days of people and cargo crisscrossing the planet, that the Eurasian genes didn’t show up sooner in North America.
Everett Forkner, a pig breeder and exporter in Richards, Mo., and a member of the National Pork Board, said he couldn’t see how two pigs infected with the different strains could wind up in close quarters. More than 20 million pigs a year are shipped internationally, but few cross an ocean.
And when Forker does sell live pigs to Asia, they are quarantined for at least 30 days before being trucked to Chicago, then isolated one or two days before being loaded onto cargo planes. They are quarantined again upon arrival in Asia for as long as 60 days, he said.
The pork industry, reeling from the bad publicity the outbreaks have wrought, has reason to downplay its part, of course. But even researchers with no connection to the industry say the flu strains from North America and Eurasia probably got together courtesy of humans.
“I don’t think it would make one squiddly bit of difference” if pig travel were banned, said Webster, the St. Jude virologist.
Scientists see two possible ways in which people may have helped assemble the building blocks of the new flu. In the first, a pig transmitted one virus to a person. That person crossed an ocean and gave it to a pig that was already infected with another one. The pig became a “mixing vessel” in which the two strains re- assorted to form the new virus.
Alternatively, a person who’d had contact with pigs on two continents picked up a virus in each place. That person, not a pig, was a mixing vessel.
As for the H1N1-infected Alberta pigs, a farmworker got the virus in Mexico, probably from a person, and brought it back. About 200 pigs, a tenth of the herd, became ill.
Animal breeder Ronald Bates of Michigan State University said that should be a warning: “If you have flu-like symptoms, don’t go near pigs.”