8. Clinical signs

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

discharge. Affected animals generally remain bright and alert and maintain a good appetite despite weakness and sluggishness [57]. Acute or subacute death may result from military tuberculosis, caused by rapid widespread dissemination, from primary or secondary lesions through the hematogenous route.

10.1 Diagnosis by clinical signs

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

nary area.

Figure 4.

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and PPD-B at site B. ©2018. JKN Kuria.

10.2 Tuberculin skin test

Clinical diagnosis may be difficult due to the chronic nature of the disease and the wide variety of symptoms, resembling other chronic debilitating conditions. The disease should be suspected on the basis of history coupled with signs of progressive emaciation, in spite of good appetite, fluctuating temperature, chronic, and moist cough dysphagia and noisy breathing. Enlargement of supramammary lymph nodes may be observed. Differential diagnosis includes contagious bovine pleuropneumonia, pasteurellosis Trueperella pyogenes pneumonia, bovine lymphosarcoma, traumatic pericarditis, and fascioliasis [63]. Animals suspected of tuberculosis infection should be thoroughly examined by palpation of all superficial lymph nodes, the udder in females and percussion and auscultation of the pulmo-

Tuberculin skin test is the standard procedure recommended by the World Organization for Animal Health (OIE) for the diagnosis of bovine TB in live animals. This test measures the delayed type hypersensitivity response to tuberculin, referred to as purified protein derivative (PPD), injected intradermally. There are two variations of the test. The single intradermal test (SITT), which uses PPD from M. bovis only (PPD-B), and the comparative intradermal test (CITT), which uses PPD-B and PPD from Mycobacteria avium, (PPD-A). In the SITT, PPD-B is injected intradermally in the neck region. A positive test is indicated by a delayed hypersensitivity reaction (Figure 4). The skin thickness at injection site is measured with a pair of calipers before and 72 hours after injection. A relative change greater than 4 mm in skin thickness at the site is considered positive for M. bovis infection [28]. The CITT is designed to address the cross-reaction between M. bovis and the M. avium. PPD-B and PPD-A are injected side by side, around 12 cm apart, and skin swelling is measured after 72 hours. The test result is considered positive, if the relative difference in the increase of skin thickness at the site of PPD-B injection is 4 mm greater than that at the site of PPD-A injection [28]. The sensitivity and specificity of the CITT has been estimated at 81–85 and 80.0, and 99.9%,

A comparative intradermal tuberculin test in a cow showing a positive reaction. PPD-A was injected at site A
