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One of the first signs of trouble was a barking cough that resounded through a North Carolina farm in August 1998. Every pig in an operation of 2400 animals sickened, with symptoms similar to those caused by the human flu: high fever, poor appetite, and lethargy. Pregnant sows were hit hardest, and almost 10% aborted their litters, says veterinary virologist Gene Erickson of the Rollins Animal Disease Diagnostic Laboratory in Raleigh. Many piglets that survived in utero were later born small and weak, and some 50 sows died.
The culprit, a new strain of swine influenza to which the animals had little immunity, left veterinarians and virologists alike puzzled. Although related flu strains in birds, humans, and pigs outside North America constantly evolve, only one influenza subtype had sickened North American pigs since 1930. That spell was suddenly broken about 4 years ago, and a quick succession of new flu viruses has been sweeping through North America’s 100 million pigs ever since. This winter, for example, up to 15% of the 4- to 7-week-old piglets on a large Minnesota farm died, even though their mothers had been vaccinated against swine flu, says veterinary pathologist Kurt Rossow of the University of Minnesota, Twin Cities.
It seems that after years of stability, the North American swine flu virus has jumped onto an evolutionary fast track, churning out variants every year. Changes in animal husbandry, including increased vaccination, may be spurring this evolutionary surge. And researchers say that the resulting slew of dramatically different swine flu viruses could spell danger for humans, too. The evolving swine flu “increases the likelihood that a novel virus will arise that is transmissible among humans,” says Richard Webby, a molecular virologist at St. Jude Children’s Research Hospital in Memphis, Tennessee.
... http://birdflubook.com/resources/WUETHRICH1502.pdf |
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