Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/1998
Publication Date: N/A
Interpretive Summary: Mycobacterium bovis causes tuberculosis in cattle as well as humans. In addition to the associated health risks, tuberculosis in cattle represents a serious obstacle to free trade and movement of cattle throughout the world. Although tuberculosis in cattle has been known for many years, the development of tuberculosis in cattle is poorly understood. To determine how and where infection and tissue damage occur in infected cattle, cattle were infected with Mycobacterium bovis and examined at various time points. The results indicate that infection and tissue damage can occur in as little as 4 weeks after infection, and that spread of infection throughout the body occurs between 4 and 6 weeks after infection. During this 2 week time, an increase in both severity and the number organs involved was observed. This information will be important to other researchers in cattle tuberculosis, and those involved in diagnosis of bovine tuberculosis. Animal health and regulatory officials will find these results useful in designing bovine tuberculosis control measures.
Technical Abstract: To examine the temporal development of tuberculous lesions in cattle, hereford cows were inoculated by intratonsilar instillation of 1.48x10*5 to 5.4x10*7 CFU of virulent Mycobacterium bovis. Tissues were collected 3 to 4 hrs, 4 wks, 6 wks,and 8 wks after inoculation. Lesions were not seen in cattle examined 3 to 4 hrs after inoculation. Medial retropharyngeal lymph nodes examined 4 wks after inoculation had cortical aggregates of macrophages without multinucleated giant cells or fibrosis. Medial or lateral retropharyngeal lymph nodes from all cattle examined 6 or 8 wks after inoculation had large coalescing granulomas with central areas of necrosis. These granulomas contained numerous macrophages, lymphocytes, plasma cells, and multinucleated giant cells. Fibrosis was revealed by Masson's trichrome staining around the granuloma periphery and around caseonecrotic debris. Cattle examined 6 or 8 wks after inoculation, had lesions in nonretropharyngeal sites including; mandibular, superficial cervical, prefemoral,tracheobronchial, mediastinal, and hepatic lymph nodes and lung. Granulomas can develop in draining lymph nodes in as little as 4 wks after intratonsilar inoculation. Morphologic changes in granulomas indicate increased cellular chemotaxis and differentiation. Spread of infection occurred by lymphatic and hematogenous routes to distant sites after establishment of primary infection in retropharyngeal lymph nodes.