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Tuberculosis is an important infectious disease of humans and domesticated
animals caused by organisms called Mycobacteria. The development of
resistant strains presents problems for successful treatment.
Tuberculosis is the term given to one of 3 forms of disease that these
organisms can cause :
- Internal granuloma formation - tuberculosis
- Skin nodules - leprosy
- Skin inflammation - opportunistic infections
Causee cause of tuberculosis is a group of aerobic, non-motile,
non-spore-forming bacteria, called Mycobacteria. They are resistant to
heat , pH and routine disinfectants. However, they are susceptible to sunlight
and 5% phenol, and they are quite susceptible to 5% household bleach.
different Mycobacteria have been associated with infection in animals :
- Mycobacterium avium-intracellulare complex -
Dogs and cats are rarely infected with this organism because they are
resistant to it, but pigs and poultry are most often infected. When dogs
or cats have been reported to be infected it has been through eating
infected meat or direct or indirect contact with infected faeces from
birds. The organism causes granulomas in various body organs. This
organism is quite resistant and can survive for over 2 years in the
environment but there is no evidence of spread to other animals or to
- Mycobacterium bovis - The main host for
this organism is cattle, and the organism can be transmitted to humans
(rarely) and other animals, including cats and dogs. The route of
infection is by drinking infected, unpasteurised milk, or by eating
infected, uncooked meat. It causes disease mainly in the gastrointestinal
tract (cats) and respiratory tract (dogs and people). M.bovis
does not survive long in the environment (less than 28 days ). In some
countries wild life reservoirs of infection eg badgers in the UK, may have
a role in the transmission of this disease between animals.
- Mycobacterium tuberculosis - Humans are the
main reservoir host for this organism but dogs and cats are susceptible to
it as well. Cats and dogs contract the infection from humans, and there
has not been any reported cases of transmission from pets to people, so
this is an inverse zoonosis. Infected people and dogs have infected sputum
and spread of the disease is by aerosol or direct contact.
- A Variant of M.tuberculosis-bovis - This
organism occurs in the UK and it has been found in cats and is thought to
originate in rodents which are their natural prey.
The Bassett Hound , Miniature Schnauzer and Siamese cat may be over-represented
in reports of M avium-complex infections. Animals with impaired immune function
are at greater risk of developing the disease if they are exposed to it..
Infected cats and dogs may not show any clinical signs of the disease.
The most common signs are :
- Dogs - respiratory signs mainly
- Weight loss
- Increased salivation
- Cats - gastrointestinal signs mainly,
- Weight loss
- Swelling of lymph nodes throughout the body
- Ascites (dropsy) - fluid accumulation in the abdomen
In addition to these signs, as a granuloma (mass) gets bigger it involves
local organs, also the organisms can spread to other parts of the body and a
wide variety of non-specific signs may occur including :
- Heart failure
- Eye disease - uveitis
- Bone fractures
- Poor healing skin ulcers
- Neurological signs
- Sudden death can occur in some cases
ComplicationsNumerous complications can occur due to spread of the organism throughout
the body. Because humans are susceptible to tuberculosis pets and other
in-contact animals should be screened whenever there is an outbreak of human
Diagnosis is made from :
- Cytology - staining and identification of Mycobacterium organisms in
- Identifying the intracellular organisms in tissue biopsies
- Tuberculin skin testing - using BCG or PPD - ok for dogs, but cats do not
develop a strong enough reaction
- Serology (blood) tests - to detect antibodies - unreliable
- Isolation of the organism by culturing them from blood, CSF, urine or
A combination of drugs is often recommended to treat tuberculosis, including :
Sometimes surgery is advised to remove a localised tuberculous lesion.
Vaccinations have not proved to be totally successful in dogs.
Guarded but poor if the disease is widely spread.
Long term problems
Updated October 2013