PARASITES AND PARASITIC DISEASES OF HORSES 



31 



ble horses. Presumably, horses become infested as a result of being 

 bitten by midges harboring the infective larvae. 



Symptoms and lesions. — These worms apparently act as irritants 

 to the tissues and thus weaken their resistance to the attacks of disease 

 germs. There is reason to believe that this may lead to the develop- 

 ment of poll evil and fistulous withers. 



Treatment. — Surgical and medicinal treatment may be employed 

 where poll evil or fistulous withers is present, but there is no treat- 

 ment for the destruction of the worms. 



Prevention. — While it is difficult to prevent horses from being 

 attacked by midges in localities where these pests occur, the avoidance 

 of swampy pastures and of pastures which con- 

 tain streams should prove beneficial in con- 

 trolling the neck threadworm. 



THREADWORMS OF THE ABDOMINAL CAVITY 



Threadworms, Setaria equina, of the body 

 cavity of the horse, also known as filarids or 

 setarids, are relatively long and slender (fig. 21) 

 and occur in various locations outside the ali- 

 mentary canal of the horse. The filar id of the 

 body cavity of the horse is from a little over 

 2 to about 5 inches in length and whitish in 

 appearance and usually occurs in the abdom- 

 inal cavity, but it has also been reported from 

 other parts of the horse's body. Immature 

 forms of this filarid, as well as of the closely 

 related filarid of cattle, sometimes occur in the 

 eyes of horses as the so-called eye worm or 

 "snake in the eye." 



Life history. — The life history of this worm 

 has not been definitely ascertained. From what 

 is known of the life histories of related forms, 

 occurring in other animals, it is probable that 

 horse filarids are transmitted by blood-sucking 

 insects. 



Symptoms and lesions. — The adult worms do 

 not appear to do much damage and are not 



known to be responsible for any definite symptoms. When the 

 immature worms get into the eye, which apparently occurs only rarely 

 in the United States, they produce considerable irritation and in time 

 may produce blindness. 



Treatment. — The presence of this parasite in the abdominal cavity 

 is seldom diagnosed during life and no treatment for it is known. 

 When the worm is present in the eye, it may be removed surgically 

 under local anesthesia. 



Prevention. — In the absence of definite knowledge concerning the 

 mode of transmission of these parasites, no definite control measures 

 can be recommended. Measures to prevent attacks by biting flies, 

 the prevention of fly breeding, and the reduction of flies by spraying 

 barns and stables with suitable preparations of DDT or other insecti- 

 cides may be of value. 



Figure 21. — Thread- 

 worms, Setaria equi- 

 na, of the abdominal 

 cavity of the horse: 

 A, male; B, female. 

 Natural size. 



