A relationship between avian carcasses and living invertebrates in the epizootiology of avian botulism.

A survey of the sources of Clostridium botulinum type C toxin possibly utilized as food by aquatic birds in an epizootic area of avian botulism in northern Utah showed that living aquatic and terrestrial invertebrates normally found in close association with dead, decomposing birds commonly carried the toxin. Of 461 samples associated with 21 species of avian carcasses, 198 were toxin-positive. Invertebrate species not normally scavengers of vertebrate tissues were less commonly and less highly toxic, particularly when captured 30 cm or more from a carcass; six of 237 samples of such aquatic invertebrates low-level toxin. Of the species tested, blow fly larvae (Calliphoridae) were the most consistently and highly toxic, although others, particularly adult and larval stages of several species of beetles (Coleoptera), contained toxin at levels probably significant in the epizootiology of the disease. An estimated 0.05 to 0.25 g of the most toxic fly larvae or 15 g of the most toxic beetles tested carried a mediam lethal dose for an adult mallard duck. Examination of stomach contents of aquatic birds dead of botulism showed that some had consumed invertebrates.