Swine flus were first detected in the 1930s, but pigs have probably had their own strains for hundreds of years, said Greg Gray, director of the Center for Emerging Infectious Diseases at the University of Iowa College of Public Health.For a long time, swine flu was the suspected culprit in the 1918 Spanish flu pandemic that killed about 50 million people.
Scientists now blame a bird flu strain, which probably infected pigs and humans simultaneously, Gray said. The pandemics of 1957 and 1968 involved strains that contained a mixture of human and avian flu viruses. Experts theorize that pigs were the mixing vessel in those cases, "but there's no smoking gun to indicate that," Olsen said. Swine flu infected 200 people in 1976, including four soldiers at Ft. Dix, N.J., one of whom died.
The virus circulated for about a month, then vanished as mysteriously as it came, according to the U.S. Centers for Disease Control and Prevention in Atlanta. In 1988, a healthy 32-year-old women who visited a pig exhibit at a county fair came down with pneumonia and died eight days later. Epidemiologists tested the exhibitors and found that 76% of them had swine flu antibodies, a sign that their immune systems had tangled with the virus, according to the CDC.
The agency typically reports a case of swine flu in humans once every year or two. But from December 2005 to February 2009, it documented 12 U.S. cases. In the current outbreak, 20 people in the U.S. have contracted swine flu, along with six in Canada. Suspected cases have been reported in France, Spain, Israel and New Zealand. Mexico is hardest hit: The government there has confirmed 22 deaths in patients with the virus, and a total of 103 deaths and 1,614 infections may be linked to swine flu.
Experts don't know why the flu is more virulent south of the border. Perhaps the genetic code of the Mexican version is slightly different, Olsen said. "It can take as little as a single amino acid change to have a substantial difference in pathogenicity," he said. Mexicans may have had longer exposure to the virus, and patients there may also be more vulnerable to secondary infections, such as pneumonia.
Compared with the control group, the farmers were 55 times more likely to have swine flu antibodies, and the spouses were 28 times more likely. "There are probably a lot of infections that are totally missed from the medical system," said Gray, who led the study. Scientists are using samples of the new swine flu strain to infect laboratory animals, including mice, guinea pigs, ferrets and primates. Researchers will test whether direct contact is necessary for transmission and whether small flu droplets can spread easily from cage to cage.
Those tests will provide clues about how easily the virus spreads and how deadly it is, Gray said. "We don't know what this virus will do," Osterholm said. "It could burn itself out in the next four to six weeks and we never see it again. It could burn itself out over a more extended period of time."But he said health officials can't ignore the chance that it could sputter out in the spring and reappear in late summer with a vengeance, as happened in 1918.
karen.kaplan@latimes.com
Scientists now blame a bird flu strain, which probably infected pigs and humans simultaneously, Gray said. The pandemics of 1957 and 1968 involved strains that contained a mixture of human and avian flu viruses. Experts theorize that pigs were the mixing vessel in those cases, "but there's no smoking gun to indicate that," Olsen said. Swine flu infected 200 people in 1976, including four soldiers at Ft. Dix, N.J., one of whom died.
The virus circulated for about a month, then vanished as mysteriously as it came, according to the U.S. Centers for Disease Control and Prevention in Atlanta. In 1988, a healthy 32-year-old women who visited a pig exhibit at a county fair came down with pneumonia and died eight days later. Epidemiologists tested the exhibitors and found that 76% of them had swine flu antibodies, a sign that their immune systems had tangled with the virus, according to the CDC.
The agency typically reports a case of swine flu in humans once every year or two. But from December 2005 to February 2009, it documented 12 U.S. cases. In the current outbreak, 20 people in the U.S. have contracted swine flu, along with six in Canada. Suspected cases have been reported in France, Spain, Israel and New Zealand. Mexico is hardest hit: The government there has confirmed 22 deaths in patients with the virus, and a total of 103 deaths and 1,614 infections may be linked to swine flu.
Experts don't know why the flu is more virulent south of the border. Perhaps the genetic code of the Mexican version is slightly different, Olsen said. "It can take as little as a single amino acid change to have a substantial difference in pathogenicity," he said. Mexicans may have had longer exposure to the virus, and patients there may also be more vulnerable to secondary infections, such as pneumonia.
- Cases go unreported
Compared with the control group, the farmers were 55 times more likely to have swine flu antibodies, and the spouses were 28 times more likely. "There are probably a lot of infections that are totally missed from the medical system," said Gray, who led the study. Scientists are using samples of the new swine flu strain to infect laboratory animals, including mice, guinea pigs, ferrets and primates. Researchers will test whether direct contact is necessary for transmission and whether small flu droplets can spread easily from cage to cage.
Those tests will provide clues about how easily the virus spreads and how deadly it is, Gray said. "We don't know what this virus will do," Osterholm said. "It could burn itself out in the next four to six weeks and we never see it again. It could burn itself out over a more extended period of time."But he said health officials can't ignore the chance that it could sputter out in the spring and reappear in late summer with a vengeance, as happened in 1918.
karen.kaplan@latimes.com
No comments:
Post a Comment