10 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



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 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 

 stomach worm, because of the tumors which they produce. The 

 tumors interfere to a considerable extent with the proper functioning 

 of the stomach. When large tumors are situated near the junction 

 of the stomach and intestine they interfere mechanically with the 

 passage of food. The most evident injury occasioned by the large 

 stomach worms is produced by the larvae which get into the skin of 

 horses where they are commonly associated with a skin disease known 

 as summer sores. 



Treatment. — A high degree of efficacy for the destruction of H. 

 muscae and H. microstoma has been obtained by the use of the fol- 

 lowing method of treatment. The animal should be fasted for from 

 18 to 24 hours and the stomach washed out by injecting through a 

 stomach tube 8 to 10 quarts of a 2-percent solution of sodium bicar- 

 bonate (baking soda) heated to 105° F. The solution tends to remove 

 the thick layer of tenacious mucus which normally covers the lining 

 of the stomach and renders the stomach worms more accessible 

 to the action of drugs. It is advisable, though not necessary, to 

 siphon off the sodium bicarbonate solution. If the solution is not 

 siphoned off, an interval of 15 to 20 minutes should elapse before 

 further treatment. Carbon disulfide should then be administered 

 in capsule or by stomach tube in a dose of 6 fluid drams (24 cubic 

 centimeters) for a 1,000-pound animal, or at a dose rate of 1.5 fluid 

 drams (6 cubic centimeters) for each 250 pounds of weight. No 

 purgative should be used with this treatment. H. megastoma in 

 stomach tumors is not affected by this treatment and is inaccessible 

 to any method of treatment known at present. 



Prevention. — Prevention of stomach -worm infestation in horses 

 involves the storage of manure in closed containers, in order to de- 

 crease the number of flies which breed in manure, or the application 

 of other control measures designed to prevent flies from breeding. 

 The use of containers for storing manure with a view to destroying 

 eggs and larvae of parasites is discussed subsequently in this circular. 

 The United States Bureau of Entomology and Plant Quarantine has 

 devised a trap designed to destroy fly maggots which breed in manure. 

 The trap is based on the observation that maggots, when fully grown, 

 migrate out of moist manure and if they are permitted to escape 

 through spaces between the boards of an open manure platform raised 

 on posts and set in a concrete basin of water, they are caught in 

 the basin and drowned. 



The advent of DDT and some of the newer insecticides has provided 

 weapons of unusual value for combating flies. The spraying of stalls 



