7. Pathology

Pathology of tuberculosis is characterized by the formation of granulomatous lesions mainly in the respiratory and alimentary tracts and associated lymph nodes.

> The lesions may be localized to few organs or tissues or disseminated to multiple sites. In the respiratory system, lesions are observed in bronchial lymph nodes, in lungs (Figure 1A) and in mediastinal lymph nodes (Figure 2). The alimentary system lesions involve the retropharyngeal, parotid, sub-maxillary, and mesenteric lymph nodes (Figure 1C), as well as the liver and portal lymph nodes, the spleen and other internal organs such as the kidneys [28]. Lesions may also be found on surfaces of body cavities such as the pleura (Figure 1B), diaphragm (Figure 1D), and peritoneum. In most cases, lesions are confined to the lymph nodes of the head region and respiratory tract [47]. The size, color, and consistency of the lesions vary widely according to the stage of infection. Lesion sizes are microscopic or large enough to involve the greater part of or the whole organ or tissue. The consistency ranges from caseopurulent, fibro-caseous fibro-calcified to calcified, but may also be thin-walled purulent cavities [4, 5, 53]. Histopathological features of a granuloma show a central area of caseous necrosis with or without calcification, surrounded by macrophages, lymphocytes, plasma cells, neutrophils, epithelioid cells, and Langhan's giant cells and

Tuberculous lesions in the mediastinal lymph nodes of a goat meat carcass. ©2018. JKN Kuria.

Diseases Caused by Bacteria in Cattle: Tuberculosis DOI: http://dx.doi.org/10.5772/intechopen.82051

The signs of tuberculosis in cattle usually vary depending on the organ systems affected. In the early stages, clinical signs are not visible and many animals with tuberculosis are clinically normal. The signs have a gradual onset characterized by progressive weakness, debility, and mild fluctuating fever. Advanced lung involvement is characterized by dyspnea, chronic moist cough, more marked in the morning and during cold weather, and reduced exercise tolerance [14]. Swollen lymph nodes of the head may be observed and involvement of internal lymph nodes may result in obstruction signs of the system or organ affected. There may be diarrhea or constipation due gastrointestinal tract involvement. Mammary tuberculosis has been found in varying proportions of animals, from 1 to 2%, up to 5.4% and is characterized by persistent mastitis and hypertrophy [40]. Infertility or abortion may result from tuberculous metritis, accompanied by chronic purulent vaginal

enclosed partially or completely by a fibrous capsule [53].

8. Clinical signs

71

Figure 2.

Figure 1.

Multiple tuberculosis lesions observed in lungs (A), pleura (B), mesentery (C) and diaphragm (D) in cattle during postmortem meat inspection.

in many organs, as in acute miliary TB, which is rapidly fatal [47, 53]. Innate non-

Pathology of tuberculosis is characterized by the formation of granulomatous lesions mainly in the respiratory and alimentary tracts and associated lymph nodes.

Multiple tuberculosis lesions observed in lungs (A), pleura (B), mesentery (C) and diaphragm (D) in cattle

specific and specific cell-mediated immunities are the main host defense mechanisms. The innate resistance may clear the initial infection and prevent mycobacteria to proliferate. Specific resistance is mediated by T-lymphocytes. They destroy infected macrophages or activate them to destroy extracellular bacilli through soluble mediators such as gamma interferon [56]. Where the host has been able to contain spread of infection, lesions consistency progress from caseous, fibro-caseous, fibro-calcified to calcified and are surrounded by a fibrous capsule. Calcified granulomas generally indicate a successful suppression of the infection by the immune response and the lesions may regress completely [53]. During pathological processes, mycobacteria are present in tuberculous tissue and in various body fluids, secretions and excretions such as milk, blood, sputum, bronchoalveolar

lavages, cerebrospinal fluid, and semen [36].

7. Pathology

Bacterial Cattle Diseases

Figure 1.

70

during postmortem meat inspection.

Figure 2. Tuberculous lesions in the mediastinal lymph nodes of a goat meat carcass. ©2018. JKN Kuria.

The lesions may be localized to few organs or tissues or disseminated to multiple sites. In the respiratory system, lesions are observed in bronchial lymph nodes, in lungs (Figure 1A) and in mediastinal lymph nodes (Figure 2). The alimentary system lesions involve the retropharyngeal, parotid, sub-maxillary, and mesenteric lymph nodes (Figure 1C), as well as the liver and portal lymph nodes, the spleen and other internal organs such as the kidneys [28]. Lesions may also be found on surfaces of body cavities such as the pleura (Figure 1B), diaphragm (Figure 1D), and peritoneum. In most cases, lesions are confined to the lymph nodes of the head region and respiratory tract [47]. The size, color, and consistency of the lesions vary widely according to the stage of infection. Lesion sizes are microscopic or large enough to involve the greater part of or the whole organ or tissue. The consistency ranges from caseopurulent, fibro-caseous fibro-calcified to calcified, but may also be thin-walled purulent cavities [4, 5, 53]. Histopathological features of a granuloma show a central area of caseous necrosis with or without calcification, surrounded by macrophages, lymphocytes, plasma cells, neutrophils, epithelioid cells, and Langhan's giant cells and enclosed partially or completely by a fibrous capsule [53].
