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 
larvee 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 lage ore 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 larve. 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 hgament without breaking them. 
Life history.—lt 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 larvee capable of infecting suscepti- 
ble horses. Presumably, horses become infested as a result of being 
bitten by midges harboring the infective larvee 
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 
