PARASITIC DISEASES OF CATTLE IN PUERTO RICO 17 
the same as for the copper sulphate alone. However, this combina- 
tion is more toxic and the amount given should be diminished if the 
full close produces unpleasant symptoms. It should not be given 
to very young animals nor to animals suffering from disease condi- 
tion other than those of parasitic origin. Calves which are in poor 
condition because of improper feeding and infestations with para- 
sites should be given small doses of this combination. The strength 
of these animals should be built up by supplying sufficient amounts 
of suitable concentrates. Animals frequently show symptoms of dis- 
tress after the first few dosings with this combination, but tolerate 
it better later. Alternating the use of this solution with the straight 
copper sulphate solution is a good practice. 
Prevention. — Same as for the stomach worms and nodular worms. 
THREAD LUNGWORM 
The lungworm (Dictyocaulus viviparus) (fig. 3, D) is found in 
the air passages, bronchi, and bronchioles of the lungs. They are 
rather large worms, ranging from 4 to 8 centimeters in length. 
Life history. — The eggs hatch in the lung and the larvae ascend 
the trachea and are expelled in coughing or swallowed and passed 
in the feces. The infective stage may be reached in 10 days or 
less. The infective larvae climb up the blades of grass when they 
are wet, as do the larvae of stomach worms and here they are taken 
in by grazing calves and make their way to the lungs. Infection 
may also be obtained from contaminated grass and from the larvae 
that have developed in damp and dirty pens. However, this is 
usually a pasture disease, and confined calves, regardless of the sys- 
tem of management, seem to be less subject to infestation with lung- 
worms than with some of the other roundworms. 
Importance. — Heavy infestations with this lungworm are not so 
common as with some of the intestinal worms. However, on many 
farms it is one of the most serious parasites of calves. Attempting 
to pasture young calves in the wet coastal areas usually results in 
massive infestations. In the dry' areas and mountain sections, calves 
having access to low, wet pastures may also become heavily infested. 
Symptoms and lesions. — The first symptom is a husky cough which 
may be followed by difficulty in breathing. The animal may die 
from suffocation, or a fatal pneumonia may develop. In the more 
common prolonged cases, the animal becomes emaciated, anemic, the 
eye sunken, and there is loss of appetite. Diarrhea is a common 
symptom. 
Treatment. — Nursing treatment appears to be the safest and most 
satisfactory in most cases. Infested calves should be confined and 
provided with a safe drinking water and a plentiful supply of dry 
hay or clean grass and concentrates. Sanitary measures should be 
taken to prevent fresh infestations in the pen. The animals should 
be treated with the copper sulphate-nicotine sulphate solution to 
remove the gastro-intestinal worms that are usually present with 
this worm. 
Prevention. — Medicinal treatment, if attempted, should be given 
by a veterinarian. In the wet coastal areas, calves up to 1 year 
of age should be confined. The confined calves should be fed on the 
