CHAPTER V. 



INFECTIOUS DISEASES PRODUCED BY 

 PROTOZOA. 



SPIROCHETOSIS OF FOWLS. 



Spirochcetosis Avium. Spirillosis of Chickens. 



Definition.— A fatal septicemia of chickens, ducks, geese, 

 and pigeons. 



Occurrence.— This disease has made its appearance in 

 several countries in enzootic form. A few outbreaks have 

 been observed in the southern part of the United States. 

 Up to the present time the disease has not attained economic 

 importance in this country. It occurs most commonly in 

 chickens where it seriously interferes with breeding. 



Etiology. —The Spirochete gallinarum (Spirillum anserum) 

 is now recognized as the causative agent. This is a blood 

 parasite, probably a flagellated protozoon. It appears as 

 fine threads, 10 to 20 microns long, spirally formed, and 

 provided with one or more cilia which show active move- 

 ments. These parasites leave the blood rapidly after the 

 fowl's death. 



Pathogenesis.— The disease is easily produced by injections 

 of virulent blood from one fowl to another of the same 

 species. Older fowls are less susceptible than younger ones. 

 The disease develops rapidly following inoculation. After 

 the second day larger numbers of the spirilla? are found in the 

 blood. 



Natural Infection.— The disease is transmitted by ticks; 

 mainly by the Argas miniatus, in some cases by the Argas 

 persicus and Argas reflexus, and in others by the Ornitho- 

 dorus moubata. The ticks exist in waste places or in wooded 

 districts. Fowls become infested by roosting where the ticks 

 occur. The ticks attach themselves to the body, and suck 

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