PARASITES AND PARASITIC DISEASES OF HORSES 5 



of the forms which have been reported from these animals normally 

 occur in other hosts and are only accidental parasites of the horse. 

 The only fluke likely to be encountered in horses in this country is 

 the common liver fluke of cattle and sheep, which is occasionally 

 found in the horse. Horses on the west coast, in the South, and in 

 the Southwest are likely to become infested with liver flukes, espe- 

 cially if they have access to pastures on which fluky sheep and cattle 

 have grazed. Liver flukes occur in the bile ducts of the liver and 

 produce a serious disease, especially in sheep. The larval forms of 

 flukes require snails as intermediate hosts and occur only on pastures 

 sufficiently wet to favor certain kinds of snails. 



Liver-fluke disease in horses has not been extensively studied, 

 because it is relatively rare in these animals. Prevention consists in 

 keeping horses off low and swampy pastures, and these precautions 

 should be especially observed in those parts of the United States where 

 liver flukes are known to occur. Such pastures favor parasites in 

 general. Farmers' Bulletin 1330 gives information on fluke control. 



Treatment. — There is no established treatment for liver-fluke in- 

 festation in the horse. However, carbon tetrachloride in small doses 

 has a specific action on the common liver fluke of sheep and is widely 

 used as a treatment for fluke infestation in these animals. Carbon 

 tetrachloride may be given with safety to adult horses in doses of 

 from 6 to 12 fluid drains (25 to 50 cubic centimeters) and in these 

 doses should be effective for the destruction of the flukes. 



TAPEWORMS 



A tapeworm is an elongated flattened worm consisting of a head 

 and a chain of segments. Each mature segment contains both male 

 and female organs. The head is provided with four suckers used to 

 attach itself to the wall of the gut. The segments of these tapeworms 

 are considerably wider than long and those which are farthest from the 

 head are the ones which contain eggs. These ripe or gravid segments 

 become detached from the rest of the chain and are expelled from the 

 body with the droppings. Beyond this point nothing is known as 

 regards the further development of horse tapeworms but in view of 

 recent information on related species in ruminants it seems possible 

 that pasture mites may serve as intermediate hosts. 



Horses are known to harbor three species of tapeworms, as follows : 



The large horse tapeworm, Anoplocephala magna (fig. 1), usually 

 is from Zy 2 to 10 inches long. The head is about two-fifths of an 

 inch in width and bears four prominent suckers. With the excep- 

 tion of those immediately adjoining the 1 head, the segments are con- 

 siderably wider than the head. This parasite occurs in the small 

 intestine and occasionally also in the stomach. 



The dwarf tapeworm of horses, Anoplocephala mamillana (fig. 2) , 

 is only from about one-fourth of an inch to 2 inches long and from 

 one-sixth to one-fourth of an inch wide; the head of this worm is 

 very minute and is barely visible to the naked eye. This tapeworm 

 occurs in the small intestine and is occasionally found in the stomach. 



A third species of tapeworm, intermediate in size between the 

 large tapeworm and the dwarf tapeworm, is known as the perfoliate 

 tapeworm, Anoplocephala perfoliata. It is usually from about 



