PARASITES AXD PARASITIC DISEASES OF HORSES 



9 



pupae. Horses may become infested with stomach worms as a 

 result of swallowing live, infected flies or infected flies which have 

 been dead a short time and still contain the live larval worms. 

 Another and possibly more common way in which horses become 

 infected with these parasites is as follows: As the flies suck the 

 moisture of the lips and nose, the larvae, which are present in the 

 mouth parts of the insects, escape, the heat and moisture of the 

 horse's body stimulating the larvae to wriggle out of the flies. Once 



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Figure 4. — Life cycle of one of the large stomach worms, Habronema muscae, of the 

 horse. The illustrations of the adult worms are enlarged about 2 times ; those of 

 the eggs are enlarged about 150 times. 



the larvae are on the lips they are readily swallowed. Those larvae 

 which get into the nasal' cavities probably wriggle into the pharynx 

 and are also swallowed. When the larvae reach the stomach they 

 are in their normal location where they settle down and develop to 

 maturity. It is possible that the small-mouthed stomach worm is 

 transmitted by the bite of the stable fly. 



Symptoms and lesions. — No definite symptoms which indicate the 

 presence of these parasites in the stomach are known. The worms 

 are injurious because of their tendency to attach themselves to and to 

 penetrate into the stomach wall and, in the case of the large-mouthed 



15390°— 30 2 



