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Ocean Watch
By Susan Scott
Monday, October 23, 2000
LAST week, I was surprised by a news story about some of Maui's shorebirds and wetland birds getting botulism. I didn't know birds could get botulism. Help clean ponds,
curb bird botulismBut get it they can. In 1998, 45,000 ducks died in Alberta, Canada, from avian botulism. That same year, thousands of wetland birds died in the United States, mostly in the western states.
Because of its prevalence in the American west, avian botulism was once called western duck sickness. Today, however, researchers have found botulism outbreaks in wetland areas throughout the world.
Avian botulism has been diagnosed in wild birds on every continent except Antarctica in at least 23 countries. It is also found throughout the United States, including Puerto Rico and Hawaii.
In the recent Maui case, the problem was in the Kealia Pond National Wildlife Refuge. More than 50 shorebirds and wetland birds died there and dozens of others were sick.
These seem like small numbers compared to North American outbreaks, but since many of Hawaii's species are endangered, even small losses are significant.
Avian botulism is bad at any time but right now our shorebirds are arriving from their arctic nesting grounds, making the outbreak even more worrisome.
The culprit in this often-fatal illness is a bacterium called Clostridium botulinum. Several strains of it can make humans deathly sick, usually after eating improperly canned foods. A different strain is killing our birds. The strain that affects birds is harmless to humans.
THE botulism germ is found naturally in the environment and is extremely widespread. You can find Clostridium botulinum in cultivated soil and pristine soil. It is common in the bottom sediments of streams, lakes, ponds and coastlines. It is also found in the intestines of fish and mammals, and in the gills and guts of crabs and other shellfish.
In spite of this pervasiveness, few people or animals get botulism. That's because the germ has two forms: rods and spores. In its active state, the bacterium looks like a tiny rod. When conditions get intolerable for the rod, it shuts down and becomes dormant. During this time, it is called a spore.
Botulinum spores can live for years and withstand boiling, freezing and drying. It is the spore form of botulinum that's common in the environment.
The conditions required for spores to become rods are precise. When oxygen is absent and temperature, alkalinity and salinity are just right, botulinum spores wake up and produce rods. During this time the bacterium releases a lethal protein called an exotoxin.
The Clostridium botulinum exotoxin is the most potent biological poison in the world. About 1/60th of an ounce can kill a human. It does this by blocking the communication between nerves and muscles, causing paralysis. The avian strain does the same in birds.
Shorebirds and wetland birds get botulism from eating worms, larvae and other invertebrates that have eaten the exotoxin. Invertebrate animals are immune to it.
The good news about avian botulism in Hawaii is that it's rare, and the recent outbreak is over. But because Kealia workers had to lower several pond levels to check the growth of exotoxin, lots of tilapia there died. If they aren't removed, the botulism cycle could begin again.
If you can lend a hand at ridding the ponds of these dead fish, call 808-875-1582. Our shorebirds, wetland birds and wildlife workers need help in fighting this nastiest of nature's toxins.
Marine science writer Susan Scott's Ocean Watch column
appears Mondays in the Star-Bulletin. Contact her at honu@aloha.net.
