US sees 2 new human infections with swine influenza viruses, CDC reports
By: Helen Branswell, The Canadian Press
The geographic spread of human infections with a new swine influenza virus has widened, the U.S. Centers for Disease Control revealed Friday as it announced a new case, this time in West Virginia.
The agency actually announced two human cases with swine-origin flu viruses on Friday. One was an infection with the H3N2 virus that has been popping up over the past few months, and a second was with a new virus, a swine-origin H1N2. That case was spotted in Minnesota.
Both cases were in children under five years old, and neither child had known contact with swine, Lyn Finelli of the CDC's influenza division said in an interview.
The widening geographic spread of the H3N2 cases has the CDC thinking these swine origin viruses may be transmitting at low levels among people, suggested Finelli, who is chief of surveillance and outbreak response in the influenza division.
"It does make us take it pretty seriously," she said of the evidence of infections in five different states — Maine, Pennsylvania, Indiana, Iowa and now West Virginia.
The virus is an influenza A virus of the H3N2 subtype. It's a distant cousin of the human H3N2 viruses that circulate every year. But it is sufficiently different, genetically, from the human virus that experts say the H3N2 component of the seasonal flu shot is unlikely to offer any protection against it.
That said, it is believed most people over the age of 20 or so would have been exposed to similar viruses in the past and would probably have some protection against this virus were it to continue to spread in people. All but one of the 11 cases spotted so far have been children under 10; the exception was a 58-year-old.
Most of the cases have experienced only mild infection though three were hospitalized. The three all had other health problems which may have contributed to the severity of their symptoms.
The swine H3N2 virus has picked up a gene from the H1N1 virus that caused the 2009 pandemic. That gene — the M gene — has been shown in animal studies to make flu viruses more transmissible.
The virus was first spotted in July and initial cases occurred in people who had contact with pigs or contact with people who had contact with pigs.
The most recent cases — the West Virginia case and a cluster of three children in Iowa a few weeks back — seem almost certainly to have been the result of viruses passing from person to person, not from pigs to people.
"We're not exactly sure how many generations these viruses are away from pigs. But it looks at least like those transmissions are person to person," Finelli said....
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