But all this took years, many years. And now it could take days. Newly evolved mibrobes could infect hordes of people with no immunity.
The jackpot events in influenza evolution occur when two different types of flu viruses happen to get into an animal cell at the same time, swapping entire chromosomes to create "reassorted" viruses.
We have a new virus in the world. It is still evolving and its ultimate trajectory cannot be seen right now.
Around Thanksgiving 2005 a teenage boy helped his brother-in-law butcher 31 pigs at a local Wisconsin slaughterhouse, and a week later the 17-year-old pinned down another pig while it was gutted. In the lead-up to the holidays the boy's family bought a chicken and kept the animal in their home, out of the harsh Sheboygan autumn. On Dec. 7, the teenager came down with the flu, suffering an illness that lasted three days. He visited a local clinic, then fully recovered, and nobody else in his family took ill.
It was an H1N1 swine influenza. Largely ignored at the time, the Wisconsin virus was a step along the evolutionary tree, leading to a virus that four years later would stun the world.
Flash-forward to April 2009, and young Édgar Enrique Hernández in faraway La Gloria, Mexico, suffers a bout of flu, found to be caused by a similar mosaic of swine/bird/human flu, also H1N1. And thousands of miles away in Cairo, the Egyptian government decides pigs are the source of disease, and orders 300,000 animals in the predominantly Muslim (therefore not pork-consuming) society slaughtered.
Each of these three incidents is related to the unfolding influenza crisis. It is the manner of human beings to seek blame during times of fear. Fingers are now pointing, either at the entire pig species Sus domestica, or at the nation of Mexico. Such exercises in blame are not only scientifically ill founded, ut are likely to prompt government actions that, at the very least, are useless and, at worst, harmful for efforts to control a pandemic.
We live in a globalized world, filled with shared microbial threats that arise in one place, are amplified somewhere else through human activities that aid and abet the germs, and then traverse vast geographic terrains in days, even hours—again, thanks to human activities and movements. If there is blame to be meted out, it should be directed at the species Homo sapiens and the manifest ways in which we are reshaping the world ecology, offering germs like the influenza virus extraordinary new opportunities to evolve, mutate and spread.
Back in 2005, the Wisconsin Division of Public Health hunted for sick pigs in Sheboygan County, but the animals the teenager had helped slaughter came from multiple farms across the area, and every farmer claimed his herd was healthy. The Wisconsin authorities forwarded blood samples from the infected teenager and his family to the Centers for Disease Control and Prevention in Atlanta. The CDC scientists discovered that the H1N1 virus had pieces of its RNA genetic material that matched a human flu first seen in New Caledonia in 1999, two swine types that had been circulating in Asia and Wisconsin for several years and an unknown avian-flu virus.
In 2006 the American Association of Swine Veterinarians reported that humans were passing their H1N1 viruses to pigs, causing widespread illness in swine herds, especially in the American Midwest. A year later at a county fair in Ohio an outbreak occurred, sickening many of the pigs, but not their human handlers. The cause was a type of H1N1 that was a close match to the Wisconsin strain, and may have been spread from human to pig.
Last year researchers from Iowa State University in Ames warned that pigs located in industrial-scale farms were being subjected to influenza infections from farm poultry, wild birds and their human handlers. Writing in The Journal of Infectious Diseases, Eileen Thacker and Bruce Janke said, "As a result of the constantly changing genetic makeup of individual influenza viruses in pigs, the U.S. swine industry is continually scrambling to respond to the influenza viruses circulating within individual production systems."
Something was changing. Pigs notoriously eat just about anything thrown their way, and rub up against each other frequently, readily passing infections within herds. Their stomachs are remarkably tolerant environs for microbes, which since ancient times have caused illness in humans who dined on raw or undercooked pork. Investigation of the 1918 influenza pandemic, which is now estimated to have killed up to 100 million people worldwide in 18 months, revealed that the viral culprit was a type H1N1 human flu that had infected pigs, and then circulated back to humans.
At the viral level, influenza is an awfully sloppy microbe that is in a constant state of mutation and evolution. Its genetic material is in the form of RNA (not DNA, as in humans), loosely collected into chromosomes. When a virus infects a cell, its chromosomes essentially fall apart into a mess, which is copied to make more viruses that then enter the bloodstream to spread throughout the body. Along the way in this copying process any other genetic material that may be lying about the cell is also stuffed into the thousands of viral copies that are made. If the virus happens to be reproducing this way inside a human cell, it picks up Homo sapiensgenetic material; from a chicken cell it absorbs avian genes; and from a pig cell it garners swine RNA. The jackpot events in influenza evolution occur when two different types of flu viruses happen to get into an animal cell at the same time, swapping entire chromosomes to create "reassorted" viruses.
Scientists prepare for a more severe strain of influenza that spreads as easily as the swine flu but is as lethal as SARS.
© Janet Crain
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