Thousands of turkeys in Minnesota have been quarantined after a strain of avian flu (H7N9) was found at a poultry farm there. Experts say that the strain is markedly less virulent than H5N1, the Asian strain that has caused more than 250 human deaths and millions of poultry deaths.

"It would appear that it's a pretty mild form of the avian influenza virus on this premise," Dave Lauer, the Minnesota Board of Animal Health's assistant director told Minnesota Public Radio. The station reports, however, that it's not unusual for more than a dozen cases of the low-pathogenic virus to be reported on commercial poultry farms in any given year.

Workers at the farm are, however, being monitored, as the strain has been known to cause some symptoms in humans, including minor respiratory problems and eye irritation. All turkeys within three miles of those infected will continued to be tested for the next six weeks, according to an Associated Press report. And if they are well after that, they may still go on to become dinner. An analysis by the U.S. Department of Agriculture (USDA) last year found that the risk of people coming down with avian influenza from consuming poultry is slim, but cooking the meat to 165 degrees Fahrenheit is a sure way to kill the virus.

The virus was discovered as part of routine testing, which has increased since new recommendations were put into place this spring. The turkeys themselves weren't showing any symptoms. "This infection is causing no illness in turkeys, but it should serve as a reminder to all of us involved with animal agriculture," said Lauer. "We need to be vigilant in observing the strictest possible bio-security to protect our animals." Of more than 42,000 U.S. commercial chicken flocks tested for influenza this year, the USDA has reported no cases of either the H5 or H7 subtypes, according to its Web site.

The most common vector for avian influenza, notes Andre Ziegler, a poultry pathologist at the University of Minnesota Veterinary Diagnostic Laboratory in St. Paul, is migrating waterfowl. They, especially the juveniles, he notes are "absolute masters" of producing "copious quantities of influenza," which can be spread to poultry that are kept outdoors.

In January, Canada confirmed 28,000 turkeys that had avian flu at a British Columbia farm. Those birds had an H5N2 virus, which is more pathogenic than the H7N9 reported in Minnesota, the nation's largest turkey producer.

Ever since its first outbreak more than 10 years ago, the highly pathogenic H5N1 Asian strain of the avian flu has proven to be fairly limited in its ability to spread from human to human.

Image of turkeys (not those infected in Minnesota) courtesy of cyanocorax via Flickr