DISEASE AND ITS CAUSES 



407 



Animal parasites may damage their hosts in a number of ways. Tapeworms absorb food 

 from the intestine which might otherwise be utihzed by the bird in which they live. Other 

 worms suck blood. Waste products of some parasites are poisonous. In the Investigation of 

 "grouse disease" in England it was observed that injuries produced by parasitic worms pro- 

 vided portals of entry for bacterial infection. 



I 



4 



/ Sowbug 

 y eaten 

 by gtouse 



Worm laivae 

 develop in 

 Sowbug 



Stomach 

 ■worm eg§s 

 passed in 

 droppings 

 of oiouse 



Adult Stomach Wojtti 



# 



\ Eggs hatch 

 \ in 



% Sowbug 



— r 



Egg eaten / 



Sowbug 



FIGURE 31. TYPICAL LIFE CYCLE OF PARASITE INVOLVING INDIRECT MODE OF TRANSMISSION 



— STOMACH WORM ( Displiaryiix spiralis) 



That the attachmcnl and jiresence of some parasites may cause extensive tissue destruction 

 and indammation has ]ic<-n repeatedly demonstrated during the Investigation by numerous 

 cases of infection by the stomach worm ( Dispharynx spiralis) of which the following is an 

 example. On December 12. 1940. a female grouse about six months old was found in the 

 field in Chenango County. This bird weighed only 292 grams (about 10' ^ ounces). Post- 

 mortem examination revealed that the saccular stomach or proventriculus was enlarged to 

 between three and four times its normal size. The cells lining the stomach were being sloughed 

 off and the tissues below the lining, where numerous stomach worms were found, had been sti- 

 mulated to excessive growth so that the stomach cavity was nearly filled with a plug of 

 mucus and destroyed stomach tissue. 



