Pandemic H1N1 has been identified in pigs, ferrets, turkeys and one cat so far. While the positive test results in animals are not unexpected, the occurrence is worrisome all the same.

“It’s actually quite disturbing,” said Dr. Jeff Bender, co-director of the Center for Animal Health and Food Safety at the University of Minnesota. “With pigs, we’re always worried about reassortment.”

The concern is that the flu virus, which mutates easily, could pick up more virulent characteristics by swapping genes with other flu viruses present in swine or other animals. That could result in a novel pathogen that spreads easily — as H1N1 already does — and is deadlier still.

H1N1 originally was named the swine flu because six of its eight genes are similar to genes in existing swine flu viruses known to be transmissible from pigs to people. However, the strain was seen in people long before it surfaced in pigs.

So far, authorities have reported no changes in the genetic makeup of the virus since it emerged from North America last spring.

There’s also been no evidence that animals infected with H1N1 are passing it to humans. To date, transmission appears to be a one-way street from people to their pets or livestock.

“These isolated events have had no impact on the dynamics of the pandemic, which is spreading readily via human-to-human transmission,” according to the World Health Organization (WHO). 

As human infections become increasingly widespread, transmission of the virus from humans to other animals is likely to occur with greater frequency. Unless the epidemiology of the pandemic changes, these will continue to pose no special risks to human health,” the WHO states.

In the United States, the U.S. Department of Agriculture (USDA) National Veterinary Services Laboratories has confirmed the H1N1 virus in swine, a ferret and a cat.

The positive test results in swine came about through a research project by investigators at the University of Minnesota and University of Iowa, funded by the U.S. Centers for Disease Control and Prevention.

Bender, the investigator from Minnesota, said the project started in 2008 with 48 samples taken from healthy swine at the Minnesota State Fair. None of those tests came back positive.

This August and September, the researchers returned to the Minnesota State Fair and also visited the state fair in South Dakota, collecting 102 samples. Again, all the swine apparently were healthy. But this time, six from Minnesota were confirmed to be positive for H1N1. Another five from Minnesota and one from South

Dakota tested positive in preliminary analyses; results of confirmatory tests are pending, according to a USDA spokeswoman.

Bender said he was surprised by the number of positives. He had expected perhaps one or two. The results tell him that “There is a lot of circulating H1N1 in people,” he said.

Whether any of the pigs became symptomatic is unknown. “No pigs were actually asked to leave early, so they remained healthy while they were at the fair,” said Bender, a DVM. The researchers did not try to track the animals on their return home.

In late October, the USDA announced it had confirmed H1N1 in a commercial swine herd in Indiana, as well.

An agency spokeswoman said reports of flu-like symptoms among the livestock caretakers prompted the producer to send in samples for analysis.

“The symptomatic pigs as well as caretakers all have fully recovered,” the spokeswoman said by e-mail. “Currently, none of the swine at the facility are showing clinical signs of the virus. Because swine that are recovered from influenza viruses are safe to move to slaughter, the Indiana facility has continued its routine processing practices.”

The USDA has reiterated time and again that it is not possible to contract the flu by eating pork.

Beyond swine, the agency’s National Veterinary Services Laboratories last month confirmed the presence of H1N1 in a pet ferret from Oregon and a house cat from Iowa. Both had symptoms of respiratory illness.

In a separate case, the Veterinary Diagnostic Center at the University of Lincoln-Nebraska identified H1N1 in another pet ferret. As with the ferret in Oregon, the people in the household had been ill, probably with the flu. Unlike the Oregon ferret, the Nebraska ferret died, according to local news reports.

The cases of H1N1 in turkeys were reported in August, involving two farms near Valparaiso, Chile. The occurrence suggests that “backyard poultry could potentially be at risk of H1N1 transmission from humans,” according to a summary of veterinary pandemic flu cases by the Oregon Veterinary Medical Association.