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1 January 2006 Identification of Primary Substrate in the Initiation of Avian Botulism Outbreaks
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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 water temperatures ≥20°C than at temperatures <20°C. This was primarily a result of carcasses being 22.2 times more likely to become maggot-laden at temperatures ≥20°C, whereas there was no difference in the occurrence of toxin within maggots developing below or above 20°C. With increasing water temperature, carcasses developed maggots significantly more rapidly and were available for a shorter time period. High density of toxic material from hatch-year Franklin's gull carcasses prior to the onset of botulism coincided with high densities of susceptible birds; hence, gull mortality had the potential to be a major initiating factor for botulism outbreaks at Eyebrow Lake. If management is deemed necessary on lakes enzootic for botulism, intensive surveillance should begin well before the anticipated onset of outbreaks to identify and remove sources of primary substrate. Managers might also consider developing and evaluating strategies to prevent the occurrence of high carcass density, particularly in areas of high nest density of species that may generate high juvenile carcass densities.

CATHERINE SOOS and GARY WOBESER "Identification of Primary Substrate in the Initiation of Avian Botulism Outbreaks," Journal of Wildlife Management 70(1), 43-53, (1 January 2006).[43:IOPSIT]2.0.CO;2
Published: 1 January 2006

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avian botulism
carcass density
Clostridium botulinum type C
Franklin's gulls
Larus pipixcan
line transect method
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