This post was originally published at Mind the Science Gap on Nov. 8, 2012.
Less than a month ago, volunteers at Sleeping Bear Dunes started noticing a problem. Dozens of loons and other aquatic birds were washing up from the Great Lakes, dead from botulism poisoning. While botulism is present in the Great Lakes and birds do die from it, biologists are reporting that the ducks are dying in far higher numbers than usual. Botulism is usually associated with improperly prepared canned goods, so why is it swimming around the Great Lakes?
First off, What is botulism?
Botulism is an illness caused by the toxin produced by a specific type of bacteria – Clostridium botulinum. This toxin causes muscle paralysis, and if untreated can result in death. Treatment can include pumping the victim’s stomach, flushing the lower gastrointestinal tract with an enema, or administration of an antitoxin. (Not a pleasant experience, I am sure.)
- Vision problems, including double vision and blurred vision
- Drooping eyelids,
- Slurred speech,
- Difficulty swallowing and dry mouth
- Muscle weakness
- Symptoms in infants can also include lethargy (excessive tiredness), lack of appetite, constipation, a weak cry, and poor muscle tone
It’s most likely that these bird deaths are caused by Type E botulism. (There are seven types of Botulism, A through G. They are essentially different strains of the organism) Type E is usually found in fish, which are then consumed by waterfowl, who then get sick and die. It is hypothesized that birds are more likely to ingest poisoned fish because they swim slowly and are easier to see.
Can people get botulism from the birds?
Type E botulism is rare in humans, but it does happen. Generally, it is good practice to wash your hands after coming in contact with any dead animal, and don’t let your dogs eat them either.
To be safe, when hunting or fishing:
- Don’t take fish or birds that look sick.
- Wear protective gloves (rubber, latex, ect.) while preparing fish or wildfowl. (Yes, annoying in the field. But remember – enema.)
- When preparing fish or fowl, do not cut open or empty the contents of the gut. Remove the gut as soon as possible.
- Cook fish and game to recommended temperatures. Only eat healthy fish and birds, since cooking may not destroy the toxin.
If you find dead birds on the lakeshore, take precautions to dispose of bird carcasses properly. Either bury them above the shoreline or dispose of them in the garbage. Take care to handle them with gloves or garbage bags.
Why the Great Lakes?
There are a few hypothesis attempting to explain why botulism causes these bird die-offs in the Great Lakes. Many center around invasive species in the lakes, notably dreissenid mussels (Dreissena bugensis and Dreissena olymorpha) and round gobies (Neogobius melanostomus). The mussels encourage algae growth, and it is hypothesized that the breakdown of this algae promotes the growth of C. botulinum. Round gobies feed on a vector species of C. botulinum, and then lose their camouflage and become easier to catch once poisoned. Warm water temperatures have also been implicated in increased botulism poisoning, however it is likely that increased temperature amplifies the effects of invasive species.
Ongoing studies are trying to determine the exact factors that are associated with botulism illness and outbreaks.
Youtube clip: Canadian wildlife biologist explaining why botulism is in the Great Lakes.