Identification of Primary Substrate in the Initiation of Avian Botulism Outbreaks

Abstract

Abstract The source of substrate for initial proliferation and toxigenesis of Clostridium botulinum prior to outbreaks of avian botulism is typically unknown. We investigated factors involved in the initiation of avian botulism outbreaks at Eyebrow Lake, Saskatchewan, Canada, and focused on the role of Franklin's gull ( Larus pipixcan ) mortality as a source of initial substrate for C. botulinum. From 1999 to 2001, hatch-year Franklin's gull carcasses were the predominant source of toxin-laden maggots found prior to outbreaks of avian botulism in waterfowl. Peak carcass density of gulls occurred 1–2 weeks prior to the onset of botulism outbreaks in waterfowl. Nest density at the beginning of the breeding season was a significant predictor of juvenile gull-carcass density. Both the proportion of gull carcasses developing maggots and the proportion of maggot samples containing toxin increased as the season progressed, and carcasses were 22.7 times more likely to develop toxin-laden maggots at mean daily wat...