Parasites and Parasitic Diseases of Dogs 



25 



double-pored tapeworm has a larval stage in fleas and the biting lice 

 of dogs. The fleas become infected while they are flea larvae feeding 

 on the organic matter in trash, the larval fleas swallowino- the tape- 

 worm eggs in this trash. Biting lice swallow the eggs while feeding 

 on the c'ontaminated skin of the dog. In these insects the tapeworm 

 eggs hatch and the escaping embryo develops to a larval tapeworm in 

 the body of the insect. When clogs, annoyed by the itching and irri- 

 tation due to these insects, hunt them out 

 and swallow them, the tapeworm larvse be- 

 come adult tapeworms in the intestine of the 

 dog. This tapeworm sometimes occurs in 

 man, especially in children, as a result of the 

 accidental swallowing of infested fleas or 

 lice by persons. 



A larger group of tapeworms is made up 

 of forms which have only two circlets of 

 hooks (fig. 26) and have a genital pore on 

 only one side of each segment (fig. 27). 

 -The thick-shelled e^^o^s do not occur in eo-o- 

 capsules but in a uterus from which some 

 intestinal contents and feces. The eggs (fig- 

 specimens in the feces. The segments, usually containing only a part 

 of the original egg content, escape in the feces and in time break up, 

 releasing the remaining eggs, which are washed about on the ground 

 and on vegetation by the rain, ^lien such eggs are swallowed by 

 a suitable host, such as sheep, cattle, swine, hares, rabbits, etc., the 



hosts varying with dif- 

 ferent species of tape- 



FiG. 25. — The common doul)le- 

 pored ts-peworm., D i p ijlid ill i)i 

 caninum. E2;g capsuie. En- 

 larged. From Stiles, 1903 



28) 



escape into the 

 occur as isolated 



worms, the 



eggs hatch 

 an 



and each releases 

 embryo which pene- 

 trates the walls of the 

 digestive tract and de- 

 velops in some tissue 

 (liver, lungs, muscles, 

 brain, intermuscular or 

 subcutaneous connec- 

 tive tissue, etc.) to 

 form a larval tape- 

 worm or bladderworm 

 (fig. 29). When these 

 bladclerworms are 

 eaten by dogs, the 

 tapeworm head in the 

 bladderworm resists 

 digestion and becomes 

 the head of a tapeworm in the intestine of the dog. 



Other dog tapeworms include such forms as the broad fish tape- 

 worm, DiphyUo'bothHuin latum^ which has two slitlike suckers in 

 place of the four rounded suckers of the preceding forms, and which 

 has its intermediate stages in fish. Dogs become infected by eating- 

 infested fish. The broad fish tapeworm also occurs in man. 



Symj)toms. — In general, tapeworms in the dog may cause dis- 

 turbances in appetite and digestion, a disposition to vomit, general 



Fig. 26. — The serrate dog tapeworm, 

 Head, viewed from the front. Euh 

 1919 



Tee Ilia pisiformis. 

 rged. From Ilall, 



