The barns at the Pullet Connection chicken farm are nearly full of young birds again, a big change from last June. That's when avian flu struck the operation near Redwood Falls. The family farm saw more than 400,000 birds destroyed and the barns — normally teeming with cheeping, fuzzy chicks — fell silent.
"The process was so difficult to go through that you never want to do it again," said Barb Frank, Pullet Connection co-owner.
Frank says that emotional toll put her and the farm's employees on edge this spring as the one-year anniversary of the outbreak approached. Infected migrating waterfowl have been leading suspects in the outbreaks. But the fall and spring waterfowl migrations came and went with no new infections.
"We're grateful to be this far down the line, and hope to move on and get rid of some of that fear that's been our underlying emotion," said Frank.
The Pullet Connection and the other infected Minnesota turkey and chicken farms are mostly back to full production. But no one could blame them if they're still worried about bird flu.
• In depth: Bird flu in Minnesota
Lou Cornicelli, wildlife research manager at the Minnesota Department of Natural Resources, says animal health researchers still don't know how the disease that struck more than one hundred Minnesota farms spread so quickly. "There's lots of gaps in knowledge regarding modes of transmission and maintenance that we just don't know," said Cornicelli.
Cornicelli says there's no doubt migrating ducks and geese played a role, but he's always been a little skeptical if they deserve all the blame.
Cornicelli says there were few waterfowl in the state when the first outbreak ocurred a year ago March. More than 6,000 field tests of ducks and geese were all negative. The virus was detected in the wild only in one hawk and one chickadee.
Some animal health researchers suspected other species were spreading the virus from the start. Maybe even small mammals. A study published last month offers some evidence to back that up. Tom DeLiberto says his team of researchers at Colorado's National Wildlife Research Center found that skunks and rabbits can spread the avian influenza virus.
"I think it's incredibly important, these findings," said DeLiberto. "It shows that there's a transmission mechanism between mammals and birds for influenza that could occur in nature."
In laboratory experiments, infected striped skunks and cottontail rabbits passed a bird flu virus to mallard ducks. DeLiberto says although this method of transmission has not been confirmed in the wild, the experiments open up a new theory to explore.
Most farmers have already taken steps to keep wild animals out of their barns, but the new findings suggest poultry producers may want to increase their vigilance, says University of Minnesota avian health professor Carol Cardona.
"I'm not sure that I'm ready to say this is the way that the virus got around, but it certainly a good thing to take a look at and understand better," said Cardona. "Is it possible that these small mammals played a role? It looks like it is a possibility and something that we should consider."
There haven't been any new bird flu cases in Minnesota and only one in the U.S. since the nation's worst outbreak of deadly avian influenza ended a year ago. But that doesn't mean it can't return. The virus has been active in other parts of the world, and there are known pathways for migrating birds to bring it to the U.S. again.