Published Date: 2007-07-14 01:00:03
Subject: PRO/AH/EDR> Botulism, avian - USA (NY)
Archive Number: 20070714.2259
BOTULISM, AVIAN - USA (NEW YORK)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 11 Jul 2007
Source: CBC News [edited]
Botulism causes waterfowl die-off in Lake Ontario
A recent die-off of hundreds of waterfowl in eastern Lake Ontario is
caused by type E avian botulism, the New York State Department of
Environmental Conservation has found. Particularly affected are gulls
and Caspian terns.
There have been no documented botulism deaths on the Canadian side of
the lake during this die-off, says Dr. Katherine Welch of the
Canadian Cooperative Wildlife Health Centre at the University of
Guelph. The situation is being monitored.
Health risks to humans are minimal, Welch said, because the toxin has
to be ingested. Anyone handling dead birds should use gloves or an
inverted shopping bag, and wash thoroughly afterwards. Welch told
CBC.ca that these waterfowl deaths occur sporadically in the Great
Lakes. In October , more than 500 loons were killed by botulism
after eating infected fish. The disease paralyzes the birds, causing
them to drown.
"The die-offs are becoming more common. We first saw them in the late
1990s. They're increasing in frequency and expanse over the last few
years," she said. They affect any fish-eating birds or scavenger
birds, including double-crested cormorants, ducks, loons, grebes and
birds from the gull family. The deaths are a concern because they can
affect the sustainability of the bird populations.
"It's a risk, especially with birds like the Caspian tern that aren't
large populations. If the adult dies, the nestlings die because
there's no one to feed them," Welch said. "If a large enough
population of adult birds die off, it could have a significant impact
on the population."
These large-scale bird deaths are due to invasive species such as
zebra mussels and round gobies. The zebra mussels create a low-oxygen
environment where the toxin can grow, then round gobies, a
bottom-dwelling fish, eat the zebra mussels and the disease works its
way up the food chain to birds. Fish with the disease swim
differently and make themselves more obvious targets to the birds,
meaning that birds are more likely to eat infected fish and thus
There's little that can be done to stop the deaths. "Until there's
some change in the ecosystem of the Great Lakes, it's going to be a
problem," Welch said. She says that anyone who finds more than 2 dead
or sick birds should notify Canadian Wildlife Services or the
Cooperative Wildlife Health Centre.
ProMED-mail Rapporteur Brent Barrett
[A photo of a zebra mussel may be seen at:
A photo of a round goby may seen at:
Botulism in avians is not usually type E, so this is an interesting case.
Though avian botulism is seen more often in other regions, it will
occur where the conditions are favorable.
The sporulating anaerobic gram-positive bacillus _C. botulinum_
elaborates 7 types of antigenically distinct neurotoxins, 4 of which
affect humans: type A, B, E, or rarely type F. Toxins types A and B
are highly poisonous proteins resistant to digestion by GI enzymes.
Approximately 50 percent of foodborne outbreaks in the USA are caused
by type A toxin, followed by types B and E.
Type C botulism occurs principally in waterfowl and other birds
living in an aquatic environment and causes tremendous losses, most
notably in waterfowl in the western US. In addition to North America,
it has been reported in birds in Europe, South Africa, Uruguay, and
Australia. In the Great Lakes region, it was first identified in 1936
in ducks on Green Bay of Lake Michigan and in 1941 in Monroe County
marshes along Lake Erie. Type C is most often associated with
limberneck paralysis in birds.
Type E botulism is connected with consumption of fish and occurs
mainly in gulls and loons, and to a lesser extent in mergansers, mute
swans, grebes, and shorebirds. It now appears that any birds or
mammals susceptible to botulinum toxin run a risk of becoming
poisoned if they scavenge dead fish. Evidence for this includes the
identification of type E toxin in a bald eagle, wood ducks, and
muskrats with fish remaining in their digestive tracts.
_C. botulinum_ spores are relatively heat-resistant, though high
temperatures and/or exposure to moist heat will kill the spores.
Toxins, on the other hand, are readily destroyed by heat and by
cooking food. Toxin production (especially type E) can occur at
temperatures as low as 3 DEG C (37.4 DEG F), i.e., inside a
refrigerator, and does not require strict anaerobic conditions.
Human illness from Type E is most often associated with improperly
smoked fish. Since the toxin is destroyed by heat, it appears that no
problem with botulism will result from eating cooked waterfowl.
(above information extracted from the Michigan Department of Natural
Resources website at
Although botulism can be difficult to manage in a scenario such as
this, it is still important to pick up the dead birds. Maggots that
grow in the carcass with harbor the botulinum toxin and when other
birds consume the maggots, a new toxicity results. So picking up the
dead birds can help control the outbreak. - Mod.TG]