Tuberculosis is a infectious bacterial disease of both domestic animals
and man caused by Mycobacterium. This disease can occur all over the world.
Before control measures were adopted, tuberculosis is one of the most serious
diseases of man and domestic animals. Any healthy animals can be infected
with the disease by inhalation the organism in various discharges excreted
from the sick animals. The discharges include exhaled air, saliva, nasal
discharges, faeces, urine and milk. The organism can usually survive outside
the host for several weeks if not exposed to direct sunlight or desiccation.
In cattle industry, the infection is the commonest in housed cattle where
healthy animals can be in close contact with the infected ones. In grazing
cattle, the disease can be spread by contaminated feed and water supplies
with infected discharges. Calves can be infected by drinking infected milk.
Because of the risk of passing the disease to humans from the infected
milk, and the economic cost to cattle industries, control and eradication
of this disease has been the aim of many countries. The most commonly used
control method is a skin test to detect the infected animals. Any infected
animals should be removed and premises cleaned and disinfected. However,
this control method is very costly and requires financial backing and a
sound organisational infrastructure.
Clinical signs:
Tuberculosis can cause abscess in the lung. Initially, the affected
animals may appear to be healthy. However, as the infection progresses,
lesions in the lung can cause a persistent but infrequent cough. In the
next stage, lymph nodes may become enlarged in the head, neck and forequarters.
Breathing may become laboured and yellowish white nasal discharge may be
observed on the affected animals. There may be a persistent gluctuating
low fever throughout the disease. In many cases, the infection can spread
to many other organs which tend to cause a general loss of condition. The
infection is always chronic and can usually last for several months. The
sick animals may gradually lose condition and eventually die.
Treatment:
There were no practical therapeutic agents for the treatment of bovine
tuberculosis until the discovery of the antituberculosis drug Isonicotinic
acid hydrazide (INH). However, the disadvantages of this drug are so great
that it is difficult to use in practice. It was shown that there were 25%
refractory cases after the use of the drug. Drug resistant strains have
been emerged in many places. Further, eliminating INH in the milk after
the treatment has been found to be difficult and there is danger of relapses
when the drug is withdrawn. Because of all these difficulties and the severe
consequences, the treatment of bovine tuberculosis is not allowed in many
countries. Emphasis should be on prevention and control.
Control measures:
There are four main approaches to the control of tuberculosis. These
are (1) test and slaughter, (2) test and segregation, (3) immunisation
and (4) chemotherapy. In test and slaughter method, tuberculin test is
used to detect the infected animals and the reacted animals are slaughtered.
This method is widely used in many western countries. In places where test
and slaughter method is impractical, test and segregation method is used,
with test and slaughter in the final stages of disease. Bacillus of Calmette
and Guerin vaccine (BCG) has been a very successful immunisation agent
in humans and it also reduces the severity of the initial disease in cattle.
However, it does not completely prevent the disease and some immunised
cattle react to the tuberculin test. Therefore, many countries have abandoned
the immunisation control option in favour of the test and slaughter method.
The chemotherapy control method is not practical due to the many drawbacks
of the antituberculosis drug INH.
WWW Sites of Relevance
World Organisation for Animal Health