Mycobacterium bovis Tuberculosis in Two Goat Farms in Multi-Host Ecosystems in Sicily (Italy): Epidemiological, Diagnostic, and Regulatory Considerations

Abstract

Mycobacterium bovis (M. bovis) is the causative agent of animal tuberculosis (bTB), infecting and causing disease in several animal species. In areas where there are complex interactions between reservoir hosts and susceptible species, the control of this pathogen is a challenge. The authors report two outbreaks of goat tuberculosis caused by M. bovis in multi-host ecosystems within two protected natural areas of Sicily, where TB is historically endemic. The first outbreak (Farm A) was identified after the incidental detection at the slaughterhouse of TB-like lesions in goat viscera ready to be disposed. Single intradermal cervical tuberculin test (SICT) was performed in Farm A on 205 goats, resulting positive in 10 (4.9%). After slaughtering, six out of ten animals showed TB-like lesions, from which M. bovis spoligotype SB0841 was isolated. The typing did not reveal any epidemiological connection with the neighboring cattle, suggesting that free-ranging type of management exposed the affected goat livestock or wildlife infected with other strains. The second outbreak (Farm B) was detected in a mixed farm (bovine, caprine, and ovine), where relapsing outbreaks of TB in cattle were registered in the previous years after performing the SICT in cohabiting goats. SICT resulted positive in 6/153 (3.9%), and two animals showed bTB-like lesions. No mycobacteria were cultured, and the final diagnosis of TB was achieved by histopathology and immunohistochemistry. The reported outbreaks highlight the importance of assessing the epidemiological, diagnostic, and regulatory critical issue, which is fundamental to optimizing the strategies of eradicating TB in the endemic multi-host ecosystem described.

Keywords: Mycobacterium bovis; goat; immunohistochemistry; multi-host ecosystem; pathology; tuberculosis.

Figure 1

Geolocation of the two Farms A and B in the Nebrodi and Madonie Parks, respectively.

Figure 2

Farm B—Typical mixed herd of goat and cattle in the Madonie Park.

Figure 3

Farm A Goat—Animal 1. Lungs and tributary lymph nodes (tracheo-bronchial and mediastinal). Lungs with multiple subpleural granulomas varying in size with a firm, elastic consistency and caseous necrosis (arrow). Mediastinal LN was enlarged and strident when cut, whitish in color, and cheesy and calcified in appearance (arrowhead).

Figure 4

Farm A Goat—Animal 1. Liver with multifocal granulomatous hepatitis. Multiple, irregularly shaped tuberculous foci, randomly distributed, on the external (a,b) and on the cut surfaces (c), with involvement of hepatic lymph-nodes (b).

Figure 5

Farm A Goat—Animal 1. Spleen displaying disseminated voluminous granulomas characterized by severe caseous necrosis.

Figure 6

Farm A Goat—Animal 2. Mammary lymph nodes with caseous tubercular lesions.

Figure 7

Farm A Goat—Animal 3. Parotid lymph nodes with caseous not calcified exudate (a). Mammary lymph node, with a caseous calcified granuloma (b). Detail from the mammary lymph node (c).

Figure 8

Farm B Goat—Animal 7. Left bronchial (a) and mediastinal (b) LNs with small, encapsulated granulomas (arrow). Impairment of hepatic parenchyma due to the presence of sub/capsular coalescing granulomatous lesions with a moderate degree of calcification (c).

Figure 9

Farm B Goat—Liver. Coalescing granulomas composed by a variable number of giant cells, epithelioid cells, macrophages, lymphocytes, and peripheral fibroplasia; hematoxilin and eosin (HE); 100* (a); B: higher magnification of the mononuclear HE, 200* (b).

Figure 10

Farm B Goat—Mediastinal lymph node. Voluminous granulomas with numerous giant cells surrounded by a variable number of epithelioid cells, macrophages, and lymphocytes; hematoxylin and eosin (HE); 200* (a); B: higher magnification of the granuloma: at the top the caseous necrotic center with calcifications surrounded by the mononuclear infiltrate with voluminous giant cells. HE, 400* (b).

Figure 11

Farm B Goat—Fine granular brown staining in the cytoplasm of epithelioid cells and multinucleated giant cells. Immunohistochemistry against M. bovis, HE counterstain, 400*.