PARASITES AND PARASITIC DISEASES OF HORSES 



29 



parasite. The midges take up the larval worms in the course of 

 piercing the skin of infested horses and, after a period of 24 to 25 

 days, the infested midges contain larvae capable of infecting suscepti- 

 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 locali- 

 ties where these pests occur, the avoidance of 

 swampy pastures and of pastures which contain 

 streams should prove beneficial in controlling 

 the neck threadworm. 



THREADWORMS OF THE ABDOMINAL CAVITY 



Threadworms, Setaria equina, of the body 

 cavity of the horse, also known as fllarids or 

 setarids, are relatively long and slender (fig. 

 21) and occur in various locations outside the 

 alimentary 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 abdominal 

 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 Fl |g^ r ^ 1, 

 filarid of cattle, sometimes occur in the eyes of abdominal cavity of the 

 horses as the so-called eye worm or "snake in maie e: xaturai^sizf' fe ~ 

 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 symp- 

 toms. 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 use of fly repellents are indicated 



-Threadworms, 



