30 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



mixture of castor oil and mineral oil, as given under the treatment for 

 large strongyles. 



Prevention. — Preventive measures with reference to the control of 

 pinworms are similar to those recommended for the large intestinal 

 roundworms and for blood strongyles. 



LUNGWORMS 



Lungworms, Dictyocaulus arnfieldi, are long, slender, whitish worms 

 and range from about 1 inch to a little over 2 inches in length. They 

 occur in the bronchi and in the bronchioles (branches of the bronchi). 



Life history. — The egg contains an embryo at the time it is depos- 

 ited by the female. The eggs hatch in the lungs, and presumably the 

 larvae are coughed up, swallowed, and eliminated from the body with 

 the manure. It is also likely that larvae are expelled with mucus during 

 coughing or sneezing. In either event, the larvae undergo their de- 

 velopment on the ground and attain the infective stage in a few days. 

 On the basis of what is known regarding the method of infestation with 

 closely related species of lungworms which occur in cattle and sheep, 

 one may assume that horses become 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 pro- 

 duce bronchitis, and the most outstanding symptom of this condition 

 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 recommended 

 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- 



