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TUBERCULOSIS
Tuberculosis is an infectious disease of most animals and humans,
characterized by the development of tubercles in any organ in the
body.
Routine, traditional examination of the bovine carcase in meat
inspection with its emphasis on lymph node inspection is based on
the pathogenesis of tuberculosis although where the disease has
been controlled the routine is justifiably modified.
Causatives in humans and animals:
 Mycobacterium tuberculosis
 Mycobacterium bovis
 Mycobacterium avium
(In cold blooded animals: M. marinum, etc. are harmless in warmblooded animals)
It may be found in rabbits and rats and are excreted by faeces. Dogs
and cats are important in transmission (M. tuberculosis and bovis) or
deers and boars in reinfection (M. bovis).
Atypical tuberculosis (facultative pathogens) in pigs (discussed
separately): Mycobacterium avium, M. smegmatis, M. phlei, M.
ulcerans, M. intracellulare, M. poikilothermorum, M. lacticola, M.
fortuitum, M butyricum (in soil, waters, plants, saw dust, bedding,
faeces, milk). These causatives are responsible for the parallergic
reactions of tuberculin test.
M. leprae, M. paratuberculosis and M. pseudotuberculosis are also
included the obligate pathogen group.
Mycobacteria are so called acid-fast (once stained, even strong acids
are not able to discolorate).
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The infection rate is increasing in humans and also in cattle (deers,
wild boar, etc.).
 Social background resulting in immunosuppressed conditions
(sexual, alcohol, drog addicts)
 The microorganisms (M. tuberculosis and M. avium, M bovis)
are also changing and drug-resistant new strains are emerging
(only surgical approach might be successful)
In 90% of AIDS patients, M. avium is present.
In non-resistant human cases, the medical treatment is by
administering:
ciprofloxacin, amikacin, kanamycin and pyrazinamide, paromomycin,
etc.
Resistance of the causative to the environment is high:
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In moisture for months
In faces at pastures for 14 days
Direct sunshine kills within 5 hours
Hidden-captured in dried excreta for up to 150 days
In manure and bedding for 3 weeks
At 10 °C for 2 years
In milk 15 days but heat treatment kills (80 °C for 20 min)
In pickled meat: 18 days, months
Decomposition is without effect: 167 days
In putrid carcase: 27 months
Deep buried carcase: years
Freezing, smoking, curing are without effect
In soft cheese for 1-2 months
It can be disinfected by applying 3% NaOH, 5% chloramines,
formalin, iodide-containing disinfecting agents.
The bacteria are excreted in sputum, faeces, milk, urine, uterine and
vaginal material and from open lymph nodes.
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PATHOGENESIS
Entering the body, primary complex develops (perfect or imperfect)
In production animals the respiratory or digestive routes of infection
are the most important. In the affected organs and associated lymph
nodes bacilli-tissue-one cell constituents’ interaction is initiated:
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Histiocytes (macrophages)
Lymphocytes
Giant cells
Fibroblasts (capsule formation thereby demarcating but antigen
can communicate)
The size of tubercule is growing by destruction/necrosis/caseation
(cheesy material) up to calcification (still live bacilli are present).
Type of reaction may be exsudative or proliferative (cellular) and it
depends on the resistance of host and virulence of microorganism
species.
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CATTLE
M. bovis- if extended, it will develop in serous surfaces of body
cavities, udder, lung, liver, spleen.
The incidence is higher in dairy herds (moisture cough, condition
loss, death). M. bovis is usually virulent and induces exsudative type
reactions.
M. tuberculosis (from sanatorium sewage, tuberculous persons). It is
non-progressive, confined to the bronchial, mediastinal lymph nodes.
M. avium- non-progressive, confined less frequently to the
retropharyngeal and more frequently to the mesenterial lymph nodes
(encapsulated, calcified).
Mode of infection in general may be
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Alimentary
Respiratory
Genital
Cutaneous
Congenital
In cattle and older calves the route of infection is mainly by
inhalation, less frequently by ingestion.
SHEEP&GOATS
M. bovis
M. tuberculosis (goat): progressive, generalized, ftal
M. avium: it is frequent in the USA where M. avium otherwise is
prevalent.
The incidence is low at open-air life and increases at housing. The
site of primary infection is the lung.
Clinically,
The pulmonary affection is accompanied by intermittent moist cough,
loss of condition, fast-difficult breathing, rough coat.
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The intestinal form is manifested in diarrhoea
CNS symptoms might develop.
PIGS
Site of infection is usually in the digestive tract.
M. bovis: traditionally the most prelevant and is closely related to
cattle if dairy products (milk, whey) is fed to pigs. Primary entry in the
tonsils followed by lymphohaematogenous generalization
Tubercules
Caseation
Calcification
If extremely virulent, stelate caseation
M. avium: Recently increasing incidence. It is localized but in USA
mostly generalized. Usually low pathogenicity and appear in form of
yellow foci in submandibular lymph nodes. No tubercle formation, in
organs tumor-like appearance.
It is also age-dependent: pig < bacon pig < boar and sows
BIRDS
M. avium, only cockatoo and parrots are susceptible to other type of
Mycobacteria (M. bovis and tuberculosis). M. avium is resistant to
environmental effects (survive for 3 years in soil and in faces or
bedding+feaces for 1 year). It is important in zoo and water birds but
not in modern, intensive farms. The bird is orally infected and
multiplicating in the digestive system and generalized process will
take place, consequently the bacterium can be found anywhere in
the organism including eggs.
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HUMANS
M. tuberculosis (also in wild and domestic animals)
M. bovis (eradication in cattle resulted in reduced incidence but gutcleaners, etc. might be affected).
M. avium- recently increasing also in humans
Depending on the resistance of host and virulence of causative, the
tuberculous process can be confined or spread. Spreading is within
organ, and through natural ducts, tubes, channels or by contiguity
e.g. from lung to pleura.
By caughing up from respiratory tract, it can be engulfed to digestive
system.
Post primary dissemination is possible from lymphatics to venousarterial circulatory system.
By breakdown, chronic lesions in lungs, udder, uterus, etc., develop
into rapidly caseating, exsudative lesions.
 Acute miliary tuberculosis
 Caseous (dry cheesy, in lymph nodes additional haemorrhages
with radiating appearance: stellate caseation indicting low
resistance)
Character of lesions
 Local circumscribed
 Exsudative (bovine, avian, human)
 Cellular reaction (pig, horse/avian), tumor-like nodules
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AFFECTION OF SELECTED SPECIFIC PARTS OF THE BODY
LUNG
Pulmonary tuberculosis is spread mainly by bronchial passages
causing gradual destruction of lung tissue by caseation and
liquefaction.
These areas are demarcated by infiltration of serous exsudate which
tend to localize the bronchial spread.
PLEURA
Way of infection is by the lymphatic route from lung manifested in
characteristic grapes-pearl appearance.
SPLEEN
It is always of haematogenous origin.
BONES/JOINTS
Cattle: Ribs, vertebrae, sternum are affected in form of spongy bones
with yellow granulation tissue.
Pigs: lumbar vertebrae (check other bones !)
PERITONEUM
Bovine
 Congenital (extension from primary lesion of liver)
 Lung (ingestion mesenteric lymph nodes or from uterus, liver)
 Pericardium (from peritoneum)
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LIVER
 Congenital (umbilical vein)
 From intestinal primary lesions by afferent lymphatics and
portal lymph nodes
 From lung affection by cough&swallow way of spread
ALIMENTARY TRACT
 Tongue, tonsils (tuberculous ulcers surrounded by hard
indurated tissue). Parotid and retropharyngeal lymph nodes
might also be affected
FEMALE SEX ORGANS
 Bilateral-symmetrical arrangement
MALE SEX ORGANS
 Haematogenous infection
UDDER
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Haematogenous spread
Lymphatic extension from an abdominal lesion
Via teat, infected syringes
Supramammary lymph nodes are not affected in chronic cases
(acute +)
MUSCLE
 Rarely involved but may occur: caseous foci in tongue,
myocardium
SKIN
 Hard painless nodules
 Single or multiple chain that follows the run of subcutaneous
lymphatic vessels. It is removed by skin at dehiding/skinning.
Prescapular, popliteal, submandibular lymph nodes, shoulder
muscles and connective tissue around the metatarsus may be
extensions of typical skin lesions. Judgement: partial
condemnations.
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DIFFERENTIAL DIAGNOSIS
 Tuberculosis like foci in submandibular lymph nodes of pigs
(yellow foci with capsule), Corynebacterium equi. It is similar
to the atypical tuberculosis cases
 Actinobacillosis
 Coccidiomycosis
 Corynebacterium pyogenes induced infections
 Various abscesses (in pigs greyish-pearl-white in sarcolumbar vertebral region, sometimes Brucella suis)
 Granulomatosis
 Mucormycosis
 Lymphomatosis
 Horse, pig- certain tumors
 Mesothelioma in bovine pleura (grape-like)
 Ziehl-Neelsen
staining,
cell-membrane
antigens
(electrophoresis, immunoblot, etc), DNS hybridization, PCR.
 Tuberculin test, gamma-interferon determination
PARASITIC INFESTATIONS
 Cheesy, calcareous, necrotic foci
 Ascaris, fasciola
 Cysticercus tenuicollis (white, spherical, capsulated nodules
with brownish, yellowish semi-solid content)
 Degenerated hydatid cysts in liver, lung (microscopically can be
distinguished)
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CONGENITAL TUBERCULOSIS IN CALVES
Characteristics
Abdominal localization and lymph nodes are affaected
In general, three forms of infection in calves
1. Tuberculosis in lungs and lymph nodes are indicating
respiratory infection
2. Tuberculosis in mesenterial lymph nodes indicate alimentary
origin of infection
3. Congenital tuberculosis: Primary infection leads to
haematogenous dissemination from the umbilical vein (from
tuberculous lesion in the placenta) to fetal liver and further to
heart and lymph nodes (rarely into lungs directly if by-passes
the liver and reach the heart and lymph nodes)
Confined to the liver and portal lymph nodes in calf: congental.