In wildlife diseases research, gross autopsy is often 

 merely the first step in determining the cause of death. 

 Detailed preparations and analysej* of sample materials, 

 followed by careful microtechnique in the laboratory, 

 are often necessary to attain positive identification. 

 (Photos by Rex G. Schmidt) 



therefore, to measure the susceptibility of several 

 species of birds to type E toxin. 



Young California gulls, 2 to 6 weeks old, were 

 found to be resistant to oral doses of type E toxin 

 as large as 160,000 MLD. Since it has been shown 

 that young gulls are not obviously affected by 

 800,000 MLD of type C toxin (to which the species 

 is known to be susceptible), it cannot be concluded 

 that they are refractor}- to type E toxin until they 

 have been subjected to much larger doses. 



The fact that the California gull can withstand 

 doses of even 160,000 MLD of type E toxin indi- 

 cates that it has some kind of immune mechanism 

 not possessed by susceptible species, and the nature 

 of this immunity is under investigation. Biolog- 

 ically active type E toxin disappears from the 

 bloodstream much more quickly than type C. In 

 one experiment, each of two mallards was given 

 an oral dose of 50,000 and 400,000 MU) of types 

 C and E toxin, respectively. In spite of the much 

 larger dose of type E, it could not be detected in 

 the blood serum 8 hours later, wliile the type C 

 toxin was still present after 57 hours. 



Adult mallards were given oral doses of as much 

 as 3.8 million MLD of type E toxin over a period 

 of 3 days without apparent ill effects. It is of 

 interest, however, that one-tenth of this dose, or 

 less, when given simultaneously with type C toxin, 

 killed 70 percent of a group of 20 birds, while the 

 type C toxin alone killed only 28 percent of a 

 group of 18. The reason for these results is being 

 sought. 



Aviun hotulisin-hlowfly 7'el<ition confirmed. — 

 Almost ever}- sununer since 1955, botulism has ac- 

 counted for the loss of a varj-ing number of birds 

 from the Bear River Research Station mallard 

 flock. Each year circumstantial evidence has 

 pointed to the blowfly as the most important source 

 of botulism toxin, presumably from feeding on 

 decomposing birds or other carcasses. 



Approximately half of a flock of 87 mallards 

 died from botulism in 1964, and probably all were 

 affected to some degree. Samples of water, aquat- 

 ic invertebrates, maggots from a duck carcass, and 

 blowflies collected in the vicinity of the holding 

 pond were tested for toxicity to laboratorj- mice. 

 Both flies and their larvae consistently contained 

 Clostridium botulinum type C toxin. With the 

 exception of samples taken next to a duck carcass, 

 the water was nontoxic. 



In each of three experiments, four ducks (two 

 protected with antitoxin) were released into an 



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