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 
these worms require snails as intermediate hosts and can maintain 
themselves only on pastures sufficiently wet to favor the occurrence 
of 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 drams (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 of a horse tapeworm is provided with 
four suckers by means of which the parasite attaches 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. The ripe or gravid segments which con- 
tain the eggs 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. 
Horses are known to harbor three species of tapeworms, as follows: 
The large horse tapeworm, Anoplocephala magna (fig. 1), usually 
is from 31% 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 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 
