Sheep - AgRIS

17.2 Infectious Diseases
In our country, much eforts of the workers on the animal health are devoted to the control
of serious epizootic diseases like sheep pox, antharx, blackquarter, foot and mouth disease,
haemorrhgic ceptlicaemia. These diseases, apart from causing economic loss to the breeders,
have been largely responsible for poor health of livestock, which, in turn, effects the economy
and cause serious human food shortage. It is therefore, imperative that utmost efforts be made
for their prompts control and eradication from the country. It is important for any profitable
enterprise that chances of loss are eliminated or reduced to a minimum. In livestock farming
the major factors of loss are the diseases; infections, infestations and clinical ailments.
Whereas clinical ailments can be done to prevent them, the infections and infestation affect a
large number of stock, often fataly, and it would amount to reducing the chances of loss or
completely eliminating them if preventive measures are taken. These measures are
collectively known as prophylactic practices. As prophylaxis means preventing, the measures
should be taken prior to the probable time of occurence and therefore different meansures
have to be taken at different periods of time in the space of a year.
The term vaccination pertains to the introduction into the hosts body of an antigenic
substance from the parasite (the whole of a virulent parasite) which will enable the host to resist
subsequent infection by a virulent parasite, by means of humeral (antibodies) and cellular
agents of immunity.
The substance that is introduced into the host‘s body is called the vaccine. It may contain
a part or whole of the organism in either dead or alive state. Most of the viral vaccines contain
living organisms whose infective potential has been reduced and are called attenuated
organisms.
i) Blackleg
Blackleg is an acute, infectious disease caused by clostridium chauvoei a gram positive
spare farming rod shaped bacterium and characterised by inflammation of muscles, severe
toxaemia and high mortality (approaches 100 per cent). The spores are highly reresistant to
the enviorment. All age groups are susceptible in sheep. Increased protein feeding of sheep
increases their susceptibility to blackleg. It is a soil borne infection. The portal of entry is
through the alimentary mucosa after ingestion of contaminated feed. In sheep, the disease is
always a wound infection. Infection of skin wounds at shearing and docking and of the naval at
birth may cause the decelopment of local lesions, When the blackleg lesions occur in the limb
musculature in sheep, there is stiff gait and the sheep is dis-inclined to move due to severe
lameness. Discolouration of the skin may be evident. There is a high fever, anorexia,
depression and death occurs very quickly. Subctaneous oedema is marked around the head.
Gas is present in the affected region. In all the cases of suspected blackleg, smears of affected
tissue should be made and material collected for bacteriologocal examination. Treatment
with penicillin is logical. Blackleg antiserum is unlikely to be of much value in treatment
unless very large doses are given. Annual vaccination with blackquarter Vaccine (polyvalent)
should be done. The vaccine is to be inoculated subcutaneously 2ml and same dose may be
carried out after ten days.
ii) Enterotoxaemia (Pulpy kidney)
This is an acute disease of sheep of all ages but primanly of lambs. It affects animals in
high state of nutrition on a lush feed, grass or grain. It causes heavy losses particularly in flocks
managed for fat lamb mutton production. Morbidity rates vary a great deal but seldom exceed
10 per cent. The mortatily rate approximates 100 percent. It is caused by clostridium
perfrengens type D. It normally inhabits the alimentary tract of sheep. Under certain conditions
the organism proliferate rapidly in the intestines and produce lethal quantity of toxin. In
lambs, the course of illness is very short often less than 2 hours and never more than 12 hours
and many are found dead without manifesting early signs. Acute cases may show little more
than severe cloric convulsions with frothing at the mouth and sudden death. Cases which
survive for a few hours show a green, pasty diarrohoea, for staggering, recumbency,
opisthotonus and severe cloric convulsions. Adult sheep show staggering and knuckling,
chewing of Jaws, salivation and rapid shallow, irregular respiration, muscle tremors, grinding
of teeth and salivation. A history of sudden death of several big single lambs justifies a
tentative diagnosis of enterotoxaemia. The postmortem findings of a distended pericardium
and congested kidney may be confirmed by identifying type DCl perfringens in the intestinal
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