AVIAN BOTULISM—ANOTHER PERSPECTIVE
Waterfowl botulism is unique among intoxications because toxin produced within its victims leads to secondary poisoning of other birds. Because of this phenomenon, the epizootiology of the carcass-maggot cycle of botulism resembles that of an infectious disease and the reproductive rate (R) of the disease could be defined as the average number of secondary intoxications attributable to a single carcass introduced into a marsh. I propose that toxin production and botulism occur commonly at a low level in many marshes and that factors which influence R determine when the disease expands into a large epizootic. A model that incorporates the number of carcasses occurring in a marsh, the probability of a carcass containing spores, the probability of a carcass persisting until toxin-bearing maggots emerge, and the contact rate between live birds and toxin, may be useful for predicting the extent of secondary-poisoning, for identifying questions for research, and as a theoretical basis for management.
PERSISTENCE OF CLOSTRIDIUM BOTULINUM TYPE C TOXIN IN BLOW FLY (CALLIPHORIDAE) LARVAE AS A POSSIBLE CAUSE OF AVIAN BOTULISM IN SPRING
Diverse samples were examined at a site of water-bird mortality, caused by Clostridium botulinum type C toxin in southern Moravia (Czechoslovakia). The toxin was detected in high concentrations in mute swan (Cygnus olor) carcasses (≤1 × 106 LD50/g) as well as in necrophagous larvae and pupae of the blow flies Lucilia sericata and Calliphora vomitoria (≤1 × 105 LD50/g) collected from them. It was detected in lower concentrations (≤1 × 103 LD50/g) in other invertebrates (ptychopterid fly larvae, leeches, sow-bugs) associated with these carcasses, and occasionally in water samples (8 LD50/ml) close to the carrion. The toxin was not detected in the samples of water, mud or invertebrates collected at a distance ≥5 m from the carcasses. The toxin-bearing larvae of L. sericata and C. vomitoria, containing 80,000 LD50/g of type C toxin, were exposed in the mud at the study site for 131 days from November to March. Although the toxin activity decreased 25-fold and 40-fold in the two samples of maggots exposed during this period, it remained very high (≤3,200 LD50/g). Birds ingesting a relatively low number of these toxic larvae (or pupae) in the spring could receive a lethal dose of the toxin.
A Microenvironment Concept of the Epizoology of Avian Botulism
11 and 21 year groups and very weak 312 and 4' year classes. 11. The average age of the herd has been reduced by one-half of a year (3.3 to 2.8) and remained at that level for two years. 12. Seventy-three per cent of Minnesota's 87 counties are represented in the successful hunter group. Residents of Becker County and other counties in the refuge area kill about three-fourths of the deer each year. 13. If action had been taken in the fall of 1942 and about 35 per cent of the deer population had been removed annually, it seems probable that about 6,000 deer could have been harvested over the 9-year period (19421950). This would have meant orderly hunting seasons, about 4 times more deer for the hunters, but more important than these, the protection of the deer range from severe overbrowsing and lowered carrying capacity resulting from such overutilization.