I 



WORMS 183 



The superfamily Ascaroidea is also well represented both in chickens 

 and wild birds. The best known of all the worms of poultry is the caecal 

 worm Heterakis gallinae, notorious as the carrier of Blackhead disease 

 [Histomonas meleagridis) . This worm has a direct life-cycle and the 

 eggs, after a period of incubation on the ground, will hatch in the 

 intestine of susceptible birds if they are swallowed in food or water. 

 Within twenty-four hours the larva has reached the caeca and 

 penetrated the mucosa, where it remains for two to five days. It then 

 returns to the lumen of the caeca where it spends the rest of its adult life. 

 Various related species are recorded from British wild birds such as the 

 sheld-duck, tawny owl, curlew, various geese and game birds. Earth- 

 worms frequently ingest the eggs and may act as transport hosts. 



Heterakis is a relatively small worm, only a few millimetres in length. 

 Worms of the genus Ascaridia are, however, much longer, sometimes 

 four to five inches long. A. galli is one of the commonest worms in 

 poultry and there are many related species in wild birds, especially in 

 game birds such as the capercaillie [Tetrao urogallus) but also in some 

 passerines. Young birds are much more frequently attacked than older 

 ones and it has been shown that after goblet cells are developed in the 

 epithelial lining of the duodenum the birds seem to become relatively 

 resistant to infection. Diet also has a considerable influence on the rate 

 of infection and when deprived of vitamins or animal protein the birds 

 easily become parasitised by these worms. 



The food of the Ascaroidea, unlike the Strongylata, consists 

 principally of the intestinal contents rather than the blood or the mucous 

 membrane of the host. Several experiments have been planned to 

 prove this. Infected chickens have been fed on beef and charcoal and 

 both ingredients were subsequently recorded from the intestines of the 

 nematodes. On another occasion a certain number of chickens infected 

 with A. galli were fed by injections and only given water by mouth. In 

 these birds the worms failed to grow, while in the control chickens, 

 which were fed in the usual manner by mouth, the parasites grew 

 normally. 



There are, of course, numbers of related roundworms (Ascaroidea) 

 which are not found in poultry. The genus Contracaecum is characteristic 

 of fish-eating mammals, birds and predatory fish. C. spiculigerum is a 

 cosmopolitan species found in the proventriculus of cormorants and 

 other sea birds such as auks, guillemots and skuas. Fish serve as first and 

 second intermediate host. Another closely related genus, Porrocaecum, 



