Mycobacterium bovis in a European bison (Bison bonasus) raises concerns about tuberculosis in Brazilian captive wildlife populations: a case report

Abstract

Background: Tuberculosis caused by Mycobacterium bovis is an important worldwide zoonosis and has been reported to cause clinical disease in several animal species, including captive wildlife. This report describes a case of M. bovis infection in a European bison from a Brazilian zoo and compiles a number of literature reports that raise concern regarding tuberculosis among captive wildlife in Brazil.

Case presentation: A 13 year-old captive-born male bison (Bison bonasus) from a Brazilian zoo began presenting weight loss, diarrhea and respiratory symptoms, which inevitably led to his death. At the animal's necropsy, inspection of the thoracic and abdominal cavities revealed multiple enlarged lymph nodes, ranging from 4 to 10 cm, and pulmonary nodules containing caseous masses with firm white materials consistent with mineralization. Histopathology findings showed a significant amount of acid-alcohol resistant bacilli compatible with Mycobacterium spp. Specimens from lymph nodes and lungs were cultured on Petragnani and Stonebrink media, and specific PCR assays of the bacterial isolate identified it as M. bovis.

Conclusion: The European bison reported herein died from a severe form of disseminated tuberculosis caused by M. bovis. A review of the available literature indicates possible widespread occurrence of clinical disease caused by M. bovis or M. tuberculosis affecting multiple animal species in Brazilian wildlife-related institutions. These likely underestimated numbers raise concern regarding the control of the disease in captive animal populations from Brazil.

Keywords: Bison; Captive animals; Mycobacterium bovis; Tuberculosis; Zoo.

Fig. 1

Necropsy findings of Mycobacterium bovis infection in a captive European bison (Bison bonasus). A Abdominal cavity demonstrating mesenteric lymph nodes ranging from 4 to 8 cm (black arrowheads). B Thoracic cavity containing multifocal to confluent granulomas (black arrowheads)

Fig. 2

Histopathology of tissue samples collected from a captive European bison (Bison bonasus) infected with Mycobacterium bovis. A Mesenteric lymph node showing multiple and confluent granulomatous inflammation with caseous necrosis and central mineralization pushing the lymph node tissues against its capsule. Haematoxylin and eosin stain. B Lung tissue with foci of granulomatous inflammation characterized by central necrosis surrounded by epithelioid macrophages. Lymphocytes, plasmocytes and occasionally well-differentiated fibroblasts were observed delimiting the granuloma. Haematoxylin and eosin stain. C Histochemistry of a section from the lung granuloma showing a great number of acid-alcohol resistant -alcohol resistant bacilli (BAAR) consistent with Mycobacterium spp. Ziehl–Neelsen stain

Fig. 3

Gel electrophoresis of PCR products for identification of Mycobacterium bovis, using primers RD 4 [13]. Lanes 1 and 11: 100 bp ladder; 2: M. tuberculosis H37Rv, 172 bp; 3: M. bovis strain AN5, 278 bp; 4–7: DNA extracted from colonies isolated in Stonebrink media; 8 and 9: empty wells; 10: negative control (water)