Bovine tuberculosis (TB) is a chronic disease of animals caused by a bacteria called
Mycobacterium bovis(M.bovis)
which is closely related to the bacteria that cause human
and avian tuberculosis.
This disease can affect practically all mammals, causing a general
state of illness, coughing and eventual death.
The name Tuberculosis comes from the nodules, called‘tubercles’, which is in the form
lymph nodes of affected animals.
Until the 19th centuary when control measures began in developed countries, it was one of the
major diseases of domestic animals throughout the world. Today TB remains an important
disease of cattle, wild animals, and is a significant zoonosis (a disease of animals which
can also infect humans).
Where is the disease found?
more prevalent in most of Africa, parts of Asia and
of the Americas.
Many developed countries have reduced or
eliminated bovine TB from their cattle population;
however significant pockets of infection remain
in wildlife in Canada, the United Kingdom, the
United States and New Zealand.
Although cattle are considered to be the true hosts
of M. bovis, the disease has been reported in
many other domesticated and non-domesticated
animals.
Isolations have been made from buffaloes, sheep, goats, equines, camels, pigs, wild boars
The disease is contagious and spread by contact
with infected domestic and wild animals.
The usual route of infection is by inhaling infected
droplets which are expelled from the lungs by
coughing.
Calves and humans can also become
Calves and humans can also become
infected by ingesting raw milk from infected cows.
Because the course of disease is slow, taking
months or years to kill an infected animal, an
animal can spread the disease to many other herd
mates before it begins to manifest clinical signs.
Therefore, movement of undetected infected
domestic animals and contact with infected wild
animals are the major ways of spreading the
disease
What is the public health risk?
Mycobacterium bovis
is not the major cause of human
tuberculosis, which is caused by
M. tuberculosis
,
but humans are susceptible to bovine TB. Humans
can be infected both by drinking raw milk from
infected cattle, or by inhaling infective droplets. It is
estimated in some countries that up to ten percent of
human tuberculosis is due to Bovine TB.
What are the clinical signs?
TB usually has a prolonged course, and symptoms
take months or years to appear. The usual clinical
signs include:
- weakness,
- loss of appetite,
- weight-loss,
- fluctuating fever,
- intermittent hacking cough,
- diarrhea,
- large prominent lymph nodes.
However, the bacteria can also lie dormant in the
host without causing disease.
How is the Disease Diagnosed?
The standard method for detection of TB is the
tuberculin test, where a small amount of antigen is
injected into the skin, and the immune reaction is
measured. Defi nitive diagnosis is made by growing
the bacteria in the laboratory, a process that takes
at least eight weeks
What is being done to prevent
or control this disease?
The standard control measure applied to TB is test
and slaughter.
Disease eradication programs consisting of post
mortem meat inspection, intensive surveillance
including on-farm visits, systematic individual
testing of cattle and removal of infected and in-
contact animals as well as movement controls have
been very successful in reducing or eliminating the
disease.
Post mortem meat inspection of animals looks
for the tubercles in the lungs and lymph nodes
(OIE
Terrestrial Animal Health Code
). Detecting
these infected animals prevents unsafe meat
from entering the food chain and allows veterinary
services to trace-back to the herd of origin of the
infected animal which can then be tested and
eliminated if needed
Pasteurisation of milk of infected animals to a
temperature suffi cient to kill the bacteria has
prevented the spread of disease in humans.
Treatment of infected animals is rarely attempted
because of the high cost, lengthy time and the
larger goal of eliminating the disease.
Vaccination is practiced in human medicine, but
it is not widely used as a preventive measure in
animals: the effi cacy of existing animal vaccines is
variable and it interferes with testing to eliminate
the disease. A number of new candidate vaccines
are currently being tested..............................................................................................
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