WILDLIFE DISEASES AND PARASITES 



Wild birds and mammals are subject to a wide 

 variety of diseases and parasites, many of which 

 show variations on hosts in different environ- 

 ments. Study of wildlife diseases, particularly 

 diseases of migratory birds, is an important Bu- 

 reau responsibility. In 1963, the Disease Labora- 

 tory at the Patuxent Center conducted research 

 on birds and mammals; the Denver Center's dis- 

 ease research concentrated on diseases and para- 

 sites of waterfowl and was carried on mainly at 

 the Bear River Substation in Utah. 



Widespread botulism losses reported. — It is dif- 

 ficult to estimate the mortality to waterfowl an- 

 nually attributable to botulism, because unob- 

 served, undiagnosed, and unreported outbreaks 

 undoubtedly occur each year. An apparent 

 change in mortality from year to year may ac- 

 tually be only a reflection of the effort, devoted to 

 field observations, laboratory diagnosis, and re- 

 porting. However, on the State and Federal ref- 

 uges in northern LTtah, where regular observations 

 have been made, estimated losses were higher in 

 1063 than in any of the 10 previous years. 



A die-off of diving ducks on Torrey Lake 

 (South Dakota) in April was shown by toxicity 

 tests in mice to have been caused by botulism. At 

 almost the same time, an outbreak on Big Grass 

 Marsh (Manitoba) was reported by the Canadian 

 Wildlife Service. During the summer and early 

 fall, the Lower Souris and Tide Lake National 

 Wildlife Refuges each suffered losses in the neigh- 

 borhood of 5,000 birds. On the Bear River Ref- 



uge, an estimated 30,000 aquatic birds perished 

 from the disease. Less severe outbreaks were re- 

 corded on Saginaw Hay, Mich., on a Richfield Oil 

 Co. marsh near Los Angeles, and on the Fish 

 Springs Refuge in Utah. At least 7,000 birds were 

 believed to have been lost on Utah State refuges. 

 Avian botulism-invertebrate relation investi- 

 gated. — For the ninth consecutive summer, aquatic 

 invertebrate studies were carried on by the Bear 

 River Research Station to explore further the 

 hypothesis that dead and decomposing carcasses 

 of small, water-living, bottom-inhabiting crea- 

 tures are used as media for growth and toxin pro- 

 duction by Clostridium botulinum type C. The 

 average number of the 2 predominant bottom- 

 fauna types, collected weekly at 80 stations in the 

 0.9-square-mile study plot, are shown in the tabu- 

 lation, along with the number of sick and dead 

 ducks picked up each week in the same area. 



On the basis of previously accumulated evidence 

 showing that certain invertebrate carcasses sup- 

 port toxin production, and that living vertebrates 

 can concentrate toxin by feeding on toxic bacterial 

 cells, a reasonable explanation of the tabulation 

 can be offered. Assuming that the decline in the 

 numbers of midge larvae in the first 11 weeks re- 

 presents a gradual die-off, it may be postulated 

 that a simultaneous gradual buildup of toxin oc- 

 curred. Because the oral lethal dose for a duck 

 is 100,000 or more times the intraperitoneal lethal 

 dose for a mouse, it would be expected that low- 

 level toxin production could occur for a consider- 

 able time before an appreciable number of birds 

 would acquire a lethal dose in feeding. The re- 

 latively stable oligochaete population, as well as 

 some of the free-swimming invertebrate species 

 (not tabulated here), may have served to concen- 

 trate and store the toxin produced in the midge 

 carcasses. 



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