ASPERGILLOSIS, AVIAN DIE-OFF - USA: (SOUTH DAKOTA) DUCKS
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A ProMED-mail post
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International Society for Infectious Diseases
Date: Tue 15 Mar 2011
Source: Rapid City Journal [edited]
Moldy corn suspected in duck die-off near Pierre
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Thousands of mallard ducks found dead in small warm-water ponds near
Pierre are believed to have died from a respiratory disease tied to
exposure to moldy corn, state and federal wildlife specialist said
Tuesday [15 MAR 2011].
More than 8000 mallards and a few pintail ducks were collected by
personnel from the state Game, Fish & Parks (GF&P) Department and the
US Fish and Wildlife Service in late January [2011] about 16 miles [26
km] northwest of Pierre. After examining some of the birds, federal
wildlife disease specialists concluded that some died from
aspergillosis, a respiratory infection caused by inhaling spores of
the aspergillus fungi.
Other ducks seem to have died from respiratory infections caused by
similar types of fungi, biologists said. Human are not considered
susceptible to the disease unless they have immune system disorders.
Exposure also may cause allergic reactions in some.
The ducks are believed to have been exposed to the fungi while
feeding on moldy corn in a silage pile at a livestock feedlot near the
small ponds they were using after nearby Lake Oahe froze up, said Andy
Lindbloom, GF&P regional game manager in Pierre.
The biggest pond, which is fed by an artesian well, is on private
land. Birds also were found on small open-water beaver dams on public
land in the area. Lindbloom believes the birds were exposed to
infectious spores from a certain area in the silage pile, then
concentrated on the ponds where they died.
"Our belief is that there was probably a hot spot in that grain,"
Lindbloom said Tuesday [15 Mar 2011]. "We believe most of that grain
is gone."
Ice fishermen on the Okobojo Creek arm of Lake Oahe notified GF&P
after finding more than 350 dead ducks on the ice, Lindbloom said. The
following day a landowner reported finding dead ducks on an open
artesian pond on his property about 3 miles [5 km] away.
"We picked up 7000 plus ducks at the well and pond," Lindbloom said.
"And we picked up another 500 or 600 at the smaller ponds that also
seemed to have the warmer water."
There was an aspergillosis-related die-off of mallards near Oahe Dam
in 1985, but it only involved a "couple hundred" ducks, Lindbloom
said. The recent die-off was unusually large but it isn't likely to
have any effect on duck hunting or the overall mallard population.
Duck hunters in South Dakota typically kill 250 000 or more ducks a
year, many of them mallards. And hundreds of thousands of mallards
gather on the Missouri River during the fall migration, with many
moving back and forth from Lake Oahe to private grain fields nearby.
Typically, that doesn't cause a problem. But this winter [2010-2011]
wasn't typical. Once Lake Oahe froze up and deep snow covered grain
fields, ducks concentrated on the smaller open ponds and fed at the
silage pile. Scott Larson, a field supervisor with the wildlife
service in Pierre, said most of the ducks that died were probably
migrating mallards that would have kept moving south if the open-water
ponds hadn't been available. "There was a little open water there, and
when they couldn't use the river they concentrated there," he said.
And because heavy snow covered grain fields, the silage pile was an
enticing food supply, he said.
"We think part of it was the snow cover. That didn't allow the
mallards to feed anywhere else but that one grain pile," he said.
After cleaning up the duck carcasses, which were later buried,
wildlife crews tried to scare ducks away from the area by using
propane cannons and other hazing devices. Despite that, at least 1000
ducks have continued to use the area.
But the die-off seems to be over, based on surveys of the area,
Larson said. "We've been up there a few more times and haven't found
anything else," he said.
Warmer weather has melted snow and opened up grain fields. And birds
also will be moving with the spring migration.
The extent of the recent die-off was unusual, Lindbloom said. "It was
pretty unique," he said. "Waterfowl has been using that area for a
long time and this is the 1st large die-off we know about. We don't
have any reason to believe it could become an annual occurrence or
anything." Even so, wildlife specialists will work with the private
landowners to monitor the area of the die-off this spring, and again
when the birds return next fall [2011].
[Byline: Kevin Woster]
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Communicated by:
ProMED-mail
[Aspergillosis is a disease produced by the mold _Aspergillus_ spp.
The mold is often found in grain substrates. Any of the molds that
produce toxic products may be found in "hot spots" within the grain.
The mold may or may not be evenly distributed in the grain, but the
presence of mold does not indicate there is a toxin being produced.
Neither does the absence of mold indicate that there is an absence of
toxin. Consequently, the grain located in the grain pile may have had
a micro environment in only one location within the grain pile that
was favorable for the production of the toxin.
Of interest is that ducks are highly susceptible to these toxins with
very small amounts causing high mortality. The growth of this mold is
encouraged when harvest of the grain is under wet conditions. This
grain pile was left outside and had been wet by the snow and rain so
it was a perfect media for the mold.
Aspergillosis is a common fungal infection in birds producing a
respiratory illness. Birds are commonly exposed to the spores of this
fungus but only develop the respiratory disease when the correct
conditions are present. Aspergillosis may be stress induced from a
variety of stresses, including such things as pre-existing illness or
malnutrition, environmental changes, shipping, reproduction, a change
in food sources, and a host of other situations. In the case of the
ducks, migration is clearly a stressful situation, draining the birds
of energy due to long flights, and the weather may have played a role
as well.
Aspergillosis may be suspected based on clinical signs, which likely
were not observed in the wild birds. However, a necropsy is the most
definitive diagnosis and is the best given the case of the wild birds.
- Mod.TG]
[The area mentioned can be seen via the HealthMap/ProMED-mail
interactive map of South Dakota at
Sr.Tech.Ed.MJ]
[see also:
2009
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Aspergillosis, avian - USA: (WA) 20091108.3864
2006
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Undiagnosed die-off, mallard ducks - USA (ID)(03): aspergillosis
20061220.3573
Undiagnosed die-off, poultry - Trinidad (02): Aspergillosis
20060112.0109]
.................................................sb/tg/mj/dk
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