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The mystery behind widespread avian flu infections in poultry flocks in Minnesota and elsewhere continues to deepen.

Minnesota officials on Wednesday announced eight additional avian flu outbreaks and three additional suspected cases that they have categorized as "presumptive positive." 

The latest report includes the first in Steele County and the state's second outbreak affecting chickens.

State Department of Natural Resources officials say more than 

 found in the wild in Minnesota yielded no findings of H5N2 influenza virus. But scientists say that is not necessarily a surprise.

 
Another 500 or so samples from ducks and geese await testing. 

DNR may test waterfowl blood for bird flu


 
"With our surveillance strategy of getting 3,000 samples from around the state, it looks like we're down to the last 250," said Lou Cornicelli, wildlife research manager with the DNR. "We should be done probably by the end of the week for sure."


Across Minnesota, DNR workers have been collecting samples of duck and goose droppings to test for the virus. Scientists suspect waterfowl have brought the H5N2 virus into the state. But Cornicelli said not one of 2,216 samples have tested positive for the virus that's so deadly to poultry.


"Not yet, no," he said. "We're still waiting on a bunch more pending samples. So we can't say for sure what might happen in the future."


Zero findings might come as a surprise because scientists say there's a high degree of certainty that waterfowl brought the disease into the state.


In Minnesota, 67 flocks are either confirmed or presumed infected. More than three million birds have been lost, costing farmers millions of dollars. But why the virus is so far not turning up in duck and geese samples is just one of the mysteries connected to the influenza outbreak. 


"I'm scratching my head about it a lot, actually," said David Stallknecht, a wildlife disease professor at the University of Georgia.


Stallknecht attributes most of the mystery about the avian flu outbreak to the newness of the disease and said this is the first time a Eurasian highly pathogenic avian flu virus has made it to North America. He said the virus may not exhibit the same types of behaviors associated with other flu bugs already in the United States.


Waterfowl can carry any of more than 100 different influenza viruses. As a general rule, scientists figure that 1 percent or less of all waterfowl carry one of those viruses.


But Stallknecht said they simply don't know enough about the deadly H5N2 virus to know the infection rate in waterfowl. The 1-percent rule may not apply.  


"It may be nowhere close to accurate," he said. "We just really don't know."


That puts the failure to find the virus in more than 2,000 Minnesota samples in a different light. If the 1-percent rule held, scientists might expect to find the current strain in about 20 samples. But if only a tenth of one percent of all waterfowl carry the disease, than the expected finding might be only two birds.


At that ratio it makes much more sense that the virus could so far escape detection, researchers say. With millions of ducks and geese passing through the state each spring, even a small infection rate would produce a lot of waterfowl carrying the disease.  


Stallknecht said the evidence is still very strong that waterfowl are spreading the disease, since scientists have found the virus in dozens of samples from other regions of the country. He said the scientific detective work is likely to find that the virus makes it into poultry barns in more than one way. He said ducks and geese may have directly caused infections in some cases.


For example, wind may pick up fecal material and carry it directly into barns. But in other cases, people likely are involved.  


"In the past, a lot of these outbreaks have spread from farm to farm with people, with equipment," Stallknecht said. There may be other routes of transmission that takes it directly from farm to farm that excludes wild birds."

Science

Health

Mark Steil

Author

Scientists believe ducks and geese carried the disease into the state. But state officials say the flu hasn't turned up in any of the 2,200 fecal samples they've examined.

Wild bird testing shows no signs yet of avian flu

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