BLACKHEAD OF TURKEYS 



293 



Smith originally called Amoeba meleagris. Tyzzer and Fabyan (1920), 

 and Tyzzer, Fabyan, and Foot (1921) showed that the disease could be 

 produced in young turkeys by the subcutaneous inoculation of diseased 

 tissues. Local lesions followed by generalized infection in the form of 

 nodules occurred. The same result occasionally followed the inoculation 

 of pigeons, whereas chickens only developed a local skin lesion. It had 

 been pointed out by Smith and Graybill (1920) that blackhead could be 

 produced in turkeys by feeding them with ova of Heterakis jjapillosa. 

 Tyzzer, Fabyan, and Foot (1921) confirmed these observations, but 

 concluded that the helminth was not the actual cause of the disease, but 

 that it was merely one of the causes of the condition favourable to invasion 

 of the body by Histomonas 

 meleagris. In support of the 

 conclusion that this organism is 

 not simply the common Tricho- 

 monas of the intestine which has 

 invaded the tissues, Tyzzer and 

 Fabyan (1920) point out that 

 blackhead may occur in young 

 birds, which appear on examina- 

 tion of the intestine to be quite 

 free from flagellates, and that 

 feeding newly hatched turkeys 

 with infected tissues does not 

 lead to the appearance of flagel- 

 lates in the gut. 



Tyzzer (1924) and Drbohlav 

 (1924) have now found that 

 young chickens contract the 

 disease when fed upon liver tissue 

 of diseased turkeys. They are 

 less susceptible to the disease than turkeys, and usually recover from 

 the acute symptoms. When the acute symptoms abate, the intestine is 

 found to harbour an organism which in many respects resembles an amoeba, 

 except that it is provided with one to four short flagella, which impart to 

 the living organism a peculiar jerky movement, as noted by Tyzzer (1920) 

 in the case of the tissue forms (Fig. 138). This infection occurs in chickens 

 which have been carefully isolated and fed on sterile food, and the par- 

 ticular organism is the only one present apart from bacteria. Control 

 chickens not fed upon liver tissue have no such infection. The recovered 

 chickens with the intestinal infection are regarded as carriers. The 

 organism, which, it is believed, is the same as the one which occurs in the 



Fig. 138. — Flagellates from the F/eces 

 OF Young Chickens infected from 

 Turkeys suffering from Blackhead 

 ( X 2,000). (Original from Giemsa 

 Stained Film prepared by Drbohlav.) 



