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Avian botulism is a paralytic, often fatal disease of birds resulting from ingestion of toxin produced by the bacterium Clostridium botulinum. Waterfowl die-offs from the botulism are usually caused by type C toxin; sporadic die-offs among fish-eating birds, such as common loons (Gavia immer) and gulls, have been caused by type E toxin.
Not enough is known about avian botulism to precisely identify the factors leading to an outbreak. When an outbreak does occur, it is usually perpetuated by a well-understood bird-maggot cycle (Figure 1).