Mar 18, 2009 (CIDRAP News) Salmonella infections have been killing more wild birds than usual in the US Southeast this winter, but the increase does not seem related to the nationwide human disease outbreak tied to tainted peanut products, according to federal wildlife scientists.
M. Kevin Keel, DVM, PhD, of the Southeastern Cooperative Wildlife Disease Study at the University of Georgia in Athens said testing so far has shown that the birds have been dying of a different Salmonella strain than the one in the human outbreak.
"It is Salmonella Typhimurium, and we see outbreaks of this type in birds every year, but usually not to this extent," Keel told CIDRAP News. Salmonella Typhimurium is also the serotype involved in the human outbreak, but the bird strain does not match genetically with the human cases, he said.
"We did do some strain typing, and our preliminary data indicate no relation" to the strain involved in the human outbreak, said Keel, who supervises the diagnostic service for the ongoing wildlife study.
Bird feed recall
Burkmann Feeds, a Kentucky company, recently recalled 150 bags of bird feed after the North Carolina Department of Agriculture found Salmonella in one sample. In a statement, Burkmann said one of its peanut suppliers had sold the company some peanuts that were subject to a recall and had not informed the company.
Burkmann makes bird feed for Wild Birds Unlimited (WBU) franchise stores in the Southeast. The recalled peanuts were used in certain lots of Burkmann's WBU Wildlife Blend and WBU Woodpecker Blend, the company said. The firm said it had recalled those lots and informed all the customers who bought the products.
In a Mar 11 press release about the recall, Wild Birds Unlimited said, "Initial tests have found no correlation between any bird deaths and the recalled food; a different strain of Salmonella was found in deceased birds in North Carolina than what we detected in the recalled food."
Western Trade Group Inc. of Port Angeles, Wash., recalled roasted peanuts in February because they contained peanuts from Peanut Corp. of America, the firm blamed for the nationwide outbreak. The firm's recall notice said the feed-grade peanuts had been sold to makers of livestock and bird feed in Iowa, Kentucky, Missouri, and North Dakota.
Pine siskins predominate
Keel said most of the Salmonella-infected dead birds have been pine siskins and goldfinches, though some cardinals and other birds have died of salmonellosis as well.
"We don't regularly get pine siskins; they're typically a more northerly bird. Periodically they come down here. They move down in extremely dense flocks. It's not uncommon to see Salmonella outbreaks among them," he said.
Keel said his lab tests birds that people find dead around their feeders and send in. The lab has tested "a couple hundred" since Januaryfar more than the four or five that are sent in for testing in a typical year.
Salmonella is not uncommon in birds found dead around feeders. But this year it's "really widespread," and it's not clear why, Keel said.
"We really don't know why this year has been much more extreme," he said. "If it hadn't occurred till the pine siskins arrived, we'd have thought it was them, but some cases occurred before they got here. They certainly are the dominant species affected now."
He said he has no suspicion that the rash of dead birds is related to the human outbreak.
A cyclical phenomenon?
Nathan Ramsay of the US Geological Survey's National Wildlife Health Center (NWHC) in Madison, Wis., said his center also has been seeing an increase in bird deaths related to Salmonella in the Southeast.
"It seems from probably around Maryland down through Appalachia we've been seeing an increase in Salmonella," he said.
Like Keel, Ramsay said the reasons are unclear. "It seems like it's a cyclical thing. Back in 1998 we had a large peak also, not only on the East Coast but also in the Midwest. It seems like every once in a while we get outbreaks that occur over a large area and in large numbers. We're not exactly sure what causes that as yet."
Ramsay, who is the lead necropsy technician at the NWHC, said the center has not run genetic tests on Salmonella isolates from birds this winter, but said "there doesn't seem to be any connection" with the human outbreak.
He said he was not aware of an unusual level of Salmonella-related bird deaths in regions other than the Southeast, with the possible exception of Washington state.
Salmonellosis is a common cause of death in birds at bird feeders, according to the NWHC. The pathogen can spread from bird to bird through direct contact or through food or water contaminated with feces from an infected bird or mammal. Infected birds may appear healthy but can shed the organism in their feces.
To reduce the spread of Salmonella, the NWHC recommends cleaning feeders with a 10% solution of bleach in water, changing feeder locations regularly, and adding more feeders to reduce crowding.
Burkmann Feeds recall news release
Mar 11 Wild Birds Unlimited recall news release
Western Trade Group Inc. recall notice
NWHC information on salmonellosis in birds