Outbreaks of a Rare Botulism Strain Stymie Scientists
The New York Times
TURKEY POINT, Ontario - When a botulism outbreak hit
this provincial park on Lake Erie in early September,
it closed the beach. Thousands of dead fish, their white
bellies glinting in the sun, washed up on the sandy shore.
Hundreds of cormorants, gulls and terns fed on the dead
sheephead, burbot and perch and quickly keeled over.
It was one of about two dozen sudden, random outbreaks
this summer and fall on the shores of Lake Erie. Over
the past four years dozens of similar outbreaks have occurred,
all involving type E botulism, a rare strain of the potent
nerve toxin. Experts say they still do not know what to
make of the outbreaks.
Biologists are holding their breath, for over the next
six weeks or so, migratory loons and the diving ducks
called mergansers will make their way from Canada to the
gulf coast for the winter. More than 8,000 common loons
have been killed by the botulism, and the species is already
in peril from overdevelopment. "This is just another hit,"
said Dr. Grace McLaughlin, a wildlife disease specialist
at the National Wildlife Health Center in Madison, Wis.
"It's pretty scary."
The botulism causing the fish and bird kills is a rare
type of the bacteria clostridium botulinum. Type C botulism,
which also kills birds, is common throughout the country,
notably in the Salton Sea in California; it occurs when
drought dries up lakes, exposing invertebrates that harbor
the toxin and are eaten by ducks and geese. Types A and
B are the kind generally found found in poorly canned
"I've seen botulism my whole career, but it's always
been C," said Dr. Ward Stone, director of the New York
State Department of Environmental Conservation's pathology
laboratory in Delmar. "When we found E, I was very surprised."
Type E is unusual because it concentrates in fish, affecting
a wider spectrum of wildlife than type C. It has been
found in very small amounts in the Great Lakes for decades,
but never for this long or in such large quantities. Something
has happened recently to increase the abundance greatly,
and biologists are trying to figure out what.
The prime suspects are three interlopers: the round
goby, a small bottom-feeding fish; hard-shelled zebra
mussels; and quagga mussels. All three species hitchhiked
to the Great Lakes from the Black and Caspian Seas in
the ballast water of international freighters - the mussels
in the past decade or so, the goby in just the past four
years. The outbreak of botulism coincides with their widespread
colonization of the lake.
Zebra and quagga mussels are thumbnail-size filter feeders
that live on the bottom and filter phytoplankton, a one-celled
alga, from the water. Paradoxically, they have made Lake
Erie's water very clear, and that may be a cause of the
Clear water allows sunlight to penetrate to greater
depths, hastening the growth of aquatic plants. Botulism
flourishes in the sort of oxygen-deprived environment
provided by decaying plant matter.
Scientists theorize that mussels may also be biological
magnifiers, concentrating the toxin as they filter water
to get nutrients or excreting the toxin into the mud around
them. When the mussels are eaten by gobies, a species
of bottom-feeding scavenger, the botulism is concentrated
further. Crippled by the toxin, the gobies thrash about
in the water and attract predatory fish, mud puppies (a
kind of salamander), mergansers, loons and other birds.
Dead or dying fish on the lakeshore are an ideal environment
for botulism. They attract scavengers like gulls and terns
- and, in one case, a bald eagle - that die when they
eat the contaminated fish. Maggots from eggs laid on the
fish become contaminated and pass the toxin along to birds
that eat them. Mergansers and loons ingest the toxin by
eating live fish.
Another contributor to the botulism outbreak may be
warming temperatures in the relatively shallow lake, whose
average depth is 60 feet. Last year was one of the rare
winters when Lake Erie did not freeze over.