28 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



which occur in cattle and sheep, one may assume that horses be- 

 come infested with lungworms as a result of swallowing the infective 

 larvae with feed or water. 



Symptoms. — When few lungworms are present in a horse, definite 

 symptoms are not produced. In heavy infestations the parasites 

 produce bronchitis, and the most 'outstanding symptom of this con- 

 dition is a cough. Excessive coughing weakens an animal, and in 

 severe cases it may result in death. 



Treatment. — Medicinal treatment for lungworm infestation is 

 unsatisfactory. 



Nursing treatment usually gives better results and is without harm 

 to the animal. Nursing treatment consists in providing nourishing 

 food, pure and uncontaminated drinking water, salt, clean, sanitary 

 quarters, and adequate shelter. The affected animals should be re- 

 moved from contaminated pastures and placed in lots or pastures 

 which are not infested with parasite eggs and larvae. This plan of 

 treatment is designed to remove the animal from areas in which it 

 is subject to gross reinfestation and improve its condition. 



Prevention. — Preventive measures are similar to those recom- 

 mended for the control of blood strongyles and the large intestinal 

 roundworm. The manure must be disposed of in a manner that 

 keeps the infective material away from the horse. 



THE NECK THREADWORM 



The large ligament of the horse's neck, known to veterinarians as 

 the ligamentum nuchae, is frequently parasitized by a long, slender 

 threadworm, Onchocerca cervicalis. The exact length of these worms 

 has not been determined owing to the difficulty of extracting them 

 from the ligament without breaking them. 



Life history. — It has been determined recently that certain biting 

 flies, commonly known as midges, are the intermediate hosts of this 

 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 dis- 

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

 velopment 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 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 filarids or setarids, are relatively long and slender (Fig. 21) 

 and occur in various locations outside the alimentary canal of the 



