The unpredictable occurrence of Type E botulism in the lower Great Lakes
Although Type E botulism was first recognized as a cause of mortality in fish-eating birds following significant die-offs of common loons and other fish-eating birds on Lake Michigan in the 1960’s, it was not seen in Canadian waters until the 1990’s. It was first observed at the Pinery Provincial Park in southeastern Lake Huron and subsequently moved southward and eastward, sequentially reaching the western and eastern basins of Lake Erie, then the Hamilton Harbour area on Lake Ontario and finally the Presqu’ile and Sandbanks areas at the eastern end of Lake Ontario. Since extending its range this far eastward, it has, in the past 2 years, also moved north and east, reaching Nottawasaga Bay in southeastern Georgian Bay last autumn.
The disease is an intoxication, caused by the ingestion of a biotoxin produced by the bacterium Clostridium botulinum, under conditions of complete absence of oxygen. Botulinum toxin is extremely potent, requiring only minute quantities to produce a condition of paralysis. Affected birds often die of drowning, due to paralysis of their respiratory muscles and an inability to hold their heads out of water. The exact circumstances under which toxin is produced and made available to the birds, is not completely known. Evidence from the stomach contents of some birds suggests that many have been eating either fish (often round gobies) or mussels (zebra or quagga mussels). However, there are many aspects of this complex chain of events that are poorly understood.
As a result, it is unpredictable where and when the disease may occur. Although 2010 was a quiet year for botulism, there were substantial mortality events in both 2009 (eastern Lake Ontario) and 2011 (Nottawasaga Bay). Typically, the greatest mortality occurs during the autumn months, as large numbers of fish-eating and mussel-eating birds – loons, mergansers, grebes, diving ducks – congregate on the Great Lakes during their southward migration.
At this time of year, there is some apprehension among wildlife biologists, park superintendents, and wildlife disease specialists as we wait to see whether or not a major event is going to occur. With luck, there won’t be, and significantly more birds will continue their migration to the south. However, our inability to predict when and where events may occur demonstrates the large gaps that exist in our knowledge and understanding of this important disease of wildlife. Filling these gaps would require a considerable effort of collaborative research among many disciplines – lake ecology, bird and fish behaviour, pathology, microbiology, epidemiology, etc. – and at the present time, resources and mechanisms to achieve this are not present.