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Parasites and Parasitosis of Sheep
1. Haemonchus contortus
Symptoms.—The location of the parasite is the abomasum where in the
beginning it buries itself under a blood-clot, sucks blood and causes a small
little ulcer at the place. When a large number of them is present, the amount
of blood lost by the animal is great and hence anaemia results. In addition
to heavy loss of blood, there is a varying amount of gastritis produced, though
the latter condition is not so severe as the loss of blood and the resultant
anaemia.
In lighter infestations, symptoms are often unnoticed, the host being able
to make up the blood lost. But when the worms are there in very large
numbers for a sufficient time and the animals continue to graze on the same
infested pasture leading to repeated infestations, the symptoms become more
pronounced. There is loss of colour, flesh and weight. The coat becomes
harsh, with the wool coming off in bunches. Usually constipation is present
but due to the invariable co-existence of the intestinal nodular worms a diarr-
hoea mixed with mucous and decomposed blood supervenes, which soils the
tail and the thighs of the lambs. They do not graze and lag behind in the
herd. When once such animals lie down they find it difficult to get up.
Oedema of the dependent parts develops and in well advanced cases, the
oedema extends forward resulting in a filled-in condition of the jowl commonly
spoken of as ' Bottle-jaw '. During this time, if the faeces is examined, ova in
very large numbers are seen. From this period, a continuous diarrhoea sets
in, with pallor of the visible mucous membrane, extreme debility and exhaus-
tion, resulting in death. Meanwhile, complications may develop due to
accumulation of dropsical effusions in the abdominal cavity and sometimes
in the thoracic cavity also. The heart is overtaxed with resultant palpitation
and effusion in the pericardial sac. Pneumonia and pleurisy with adhesions
are not uncommon sequelae.
Diagnosis.—It is easy when lambs are particularly thin and anaemic and
the dependent parts are swollen, particularly under the jaw. The blood is thin
and watery. The blood picture shows anaemia with anisocytosis, poikilo-
cytosis, punctate basophilia and an increased white-cell count at the advanced
stage, particularly the eosinophiles if the animal tides over the infestation.
Faecal examination reveals a high egg count which is characteristic of
Haemonchus.
Lesions.—Careful post-mortem examinations made on cases died of
haemonchosis, reveal a varying intensity of gastritis. In mild and early cases,
the mucous membrane is congested with haemorrhagic spots, strewn over the
surface. The worms are seen wobbling in the half digested stomach contents
mixed with mucous. The mucous membrane comes off in patches revealing
worms entangled in blood and mucous. In more longstanding cases, there is
thickening of the stomach wall and pallor of the mucous membrane, with
patches of ulceration and sometimes necrosis. In the early pre-adult stage,
the worms live in the sub-mucosa causing a varying amount of gastritis and
later return to the surface, having become adults to breed and discharge ova.
Pathology.—As a result of severe gastritis, the stomach is prevented from
functioning to some extent. In the beginning of the infestation, the irritation