Bovine tuberculosis in African buffalo (Syncerus caffer): Progression of pathology during infection

Bovine tuberculosis (BTB) is a zoonotic disease of global importance endemic in African buffalo (Syncerus caffer) in sub-Saharan Africa. Zoonotic tuberculosis is a disease of global importance, accounting for over 12,000 deaths annually. Cattle affected with BTB have been proposed as a model for the study of human tuberculosis, more closely resembling the localization and progression of lesions in controlled studies than murine models. If disease in African buffalo progresses similarly to experimentally infected cattle, they may serve as a model, both for human tuberculosis and cattle BTB, in a natural environment. We utilized a herd of African buffalo that were captured, fitted with radio collars, and tested for BTB twice annually during a 4-year-cohort study. At the end of the project, BTB positive buffalo were culled, and necropsies performed. Here we describe the pathologic progression of BTB over time in African buffalo, utilizing gross and histological methods. We found that BTB in buffalo follows a pattern of infection like that seen in experimental studies of cattle. BTB localizes to the lymph nodes of the respiratory tract first, beginning with the retropharyngeal and tracheobronchial lymph nodes, gradually increasing in lymph nodes affected over time. At 36 months, rate of spread to additional lymph nodes sharply increases. The lung lesions follow a similar pattern, progressing slowly, then accelerating their progression at 36 months post infection. Lastly, a genetic marker that correlated to risk of M. bovis infection in previous studies was marginally associated with BTB progression. Buffalo with at least one risk allele at this locus tended to progress faster, with more lung necrosis. The progression of disease in the African buffalo mirrors the progression found in experimental cattle models, offering insight into BTB and the interaction with its host in the context of naturally varying environments, host, and pathogen populations.

International audience

Sadly, despite a previous warning of a cattle tuberculosis (TB) crisis (Hancox 1998a,b), there has been a steady worsening of the situation with a very real risk to public health. Bovine TB is now back to 1960s levels in Britain, from a low point in the mid‐1970s of 89 herds and 600 cases to 872 new herds and 7000 cases in 1999. TB has spread from tiny south‐west ‘hot spots’ to an area from Cornwall up to Cheshire/Derbyshire (distribution maps in Krebs 1997). Irish incidence has gone back to 1970s levels with over 45 000 cases last year. Over the last 30 years attention has focused to such an extent on badgers (Meles meles L.) as the ‘main source’ of further herd outbreaks, that amidst the confused debate over this ‘highly complex and emotive issue’, it is quite extraordinary that the importance of cattle‐to‐cattle transmission is seriously questioned (Griffin and Dolan 1995; O'Reilly and Daborn 1995; Gardner 1999; Anonymous 2000; Bourne 2000; Morrison et al. 2000), and this despite a century's experience of cattle TB schemes in over a hundred countries to the contrary! Out of five main schemes the widespread success of ‘area eradication’ rests on a robust scientific base as the most cost‐effective and sustainable means of minimizing or preventing transmission within the cattle population. But whereas early on, most test reactors are lesioned and infectious, late on most ‘reactors’ do not have ‘tubercle’ lesions and are not infectious because they do not have TB, hence the confusion (Francis 1947).

Tuberculosis pathology was studied on 19 African buffalo (Syncerus caffer) from a herd in the Hluhluwe-iMfolozi Park in South Africa. The animals tested positive with the comparative intradermal tuberculin test and were euthanized during a test-and-cull operation to decrease prevalence of bovine tuberculosis (bTB) in the park. The lymph nodes and lungs were examined grossly for presence of tuberculous lesions, which were scored on a 0-5 scale for macroscopic changes. The gross lesions were examined histologically and classified into grade I, II, III, or IV according to a grading system used for bTB lesions in domestic cattle. Macroscopic lesions were limited to the retropharyngeal, bronchial, and mediastinal lymph nodes and the lungs. The most frequently affected lymph nodes were the bronchial (in 16 animals) and mediastinal (in 11 animals). All four grades of microscopic lesions were observed, grade II lesions were the most frequent. Mycobacterium bovis was detected by PCR in 8 out of 19 animals, and acid-fast bacilli were seen in 7 out of 19 animals, together both techniques identified mycobacteria in 5 out of 19 animals. Lesions were paucibacillary, as acid-fast bacilli were only rarely observed. The absence of lesions in the mesenteric lymph nodes and the high frequency of lesions in respiratory tract associated lymph nodes suggest that the main route of M. bovis infection in African buffalo is by inhalation.

Distribution of Lesions in Red and Fallow Deer Naturally Infected with Mycobacterium bovis

Risk factors of tuberculosis in human and its association with cattle TB in Nepal: A one health approach

Tuberculosis caused by Mycobacterium bovis is endemic in the African buffalo (Syncerus caffer) population in the Kruger National Park and other conservation areas in South Africa. The disease has been diagnosed in a total of 21 free ranging or semi-free ranging wildlife species in the country with highly variable presentations in terms of clinical signs as well as severity and distribution of tuberculous lesions. Most species are spillover or dead-end hosts without significant role in the epidemiology of the disease. White rhinoceroses (Ceratotherium simum) are translocated from the Kruger National Park in substantial numbers every year and a clear understanding of their risk to manifest overt tuberculosis disease and to serve as source of infection to other species is required. We report the findings of experimental infection of three white rhinoceroses with a moderately low dose of a virulent field isolate of Mycobacterium bovis. None of the animals developed clinical signs or disseminated disease. The susceptibility of the white rhinoceros to bovine tuberculosis was confirmed by successful experimental infection based on the ante mortem isolation of M. bovis from the respiratory tract of one rhinoceros, the presence of acid-fast organisms and necrotizing granulomatous lesions in the tracheobronchial lymph nodes and the detection of M. bovis genetic material by PCR in the lungs of two animals.

Associations between cytokine gene expression and pathology in Mycobacterium bovis infected cattle

Field application of immunoassays for the detection of Mycobacterium bovis infection in the African buffalo (Syncerus caffer)

Bovine tuberculosis (bTB) is a transmissible disease of livestock with high economic consequences. To estimate the prevalence and risk factors associated to bTB, a study was conducted in Algerian abattoirs involving detailed inspection, microscopic examination, culture of tissue samples and molecular investigation. Out of 3848 bovine carcasses examined, 184 (4.78%) exhibited visible lesions suggestive of tuberculosis (TB). Anatomically 84.8% of the lesions were found in thoracic cavity. Lesions were predominant in tracheobronchial lymph nodes (71.7%), lung tissue (4.9%) and retropharyngeal lymph nodes (4.9%), followed by hepatic tissue (3.8%) and retrohepatic lymph nodes (3.8%). Less frequently, lesions were observed in prescapular lymph nodes (1.6%), digestive tract (0.5%) and kidney (0.5%). The study revealed statistically high (p<0.0001) infection rate in males (78.8%) than females (21.2%). A Significant difference (p<0.05) in TB infection rate was recorded between the three age/animal categories: 2 to 6 years (42.9%), <2 years (39.1%) and 6 years (17.9%). Analysis of data recorded in the present study showed a high significant variation (p<0.0001) in seasonal prevalence of bTB with a higher frequency during dry season than in rainy season. Microscopic examination of 105 samples revealed that 60 (57.1%) harbored acid-fast-bacilli (AFB) and 45(42.9%) were negative (p0.05). Culture yielded 60 (57.1%) positive, 43(41%) negative and only 2(1.9%) samples were contaminated. In PCR RD9 analysis, all isolated strains were belong to the Mycobacterium tuberculosis complex (MTC). The present findings can serve as background information to elaborate an adequate eradication program for bTB in Algeria.

Human Mycobacterium bovis infection in the United Kingdom: Incidence, risks, control measures and review of the zoonotic aspects of bovine tuberculosis

The hallmark lesion of tuberculosis in humans and animals is the granuloma. The granuloma represents a distinct host cellular immune response composed of epithelioid macrophages, lymphocytes, and multinucleated giant cells, often surrounding a caseous necrotic core. Within the granuloma, host-pathogen interactions determine disease outcome. Factors within the granulomas such as cytokines and chemokines drive cell recruitment, activity, function and ultimately the success or failure of the host’s ability to control infection. Hence, an understanding of the granuloma-level cytokine response is necessary to understand tuberculosis pathogenesis. In-situ cytokine expression patterns were measured using a novel in situ hybridization assay, known as RNAScope® in granulomas of the lungs, tracheobronchial lymph nodes and caudal mediastinal lymph nodes of cattle experimentally infected with Mycobacterium bovis via aerosol exposure. In spite of microscopic morphological similarities, significant differences were seen between late stage granulomas of the lung compared to those of the tracheobronchial lymph nodes for IL-17A, IFN-γ, TGF-β, IL10 and IL-22 but not for TNF-α. Additionally, significant differences were noted between granulomas from two different thoracic lymph nodes that both receive afferent lymphatics from the lungs (i.e., tracheobronchial and caudal mediastinal lymph nodes) for TNF-α, IL-17A, IFN-γ, TGF-β and IL-10 but not for IL-22. These findings show that granuloma morphology alone is not a reliable indicator of granuloma function as granulomas of similar morphologies can have disparate cytokine expression patterns. Moreover, anatomically distinct lymph nodes (tracheobronchial vs caudal mediastinal) differ in cytokine expression patterns even when both receive afferent lymphatics from a lung containing tuberculoid granulomas. These findings show that selection of tissue and anatomic location are critical factors in assessing host immune response to M. bovis and should be considered carefully.

Detection of Mycobacterium bovis infection in African buffaloes (Syncerus caffer) using QuantiFERON®-TB Gold (QFT) tubes and the Qiagen cattletype® IFN-gamma ELISA

Objective To examine the temporal development of tuberculous lesions in cattle inoculated with Mycobacterium bovis. Animals 15 mature crossbred cows obtained from a herd with no history of M bovis infection. Procedure Inoculation of cattle was done by intratonsilar instillation of 1.48 × 105 to 5.4 × 107 colony-forming units of M bovis strain 2045T. At 3 to 4 hours, 4 weeks, 6 weeks, and 8 weeks after inoculation, tissues were examined for gross and microscopic lesions and processed for isolation of M bovis. Results Retropharyngeal lymph nodes from cattle examined 4 weeks after inoculation contained microgranulomas consisting of aggregates of macrophages with few neutrophils. Retropharyngeal lymph nodes from all cattle examined 6 and 8 weeks after inoculation contained multiple, large, coalescing granulomas consisting of central areas of necrosis with mild fibrosis, numerous macrophages, lymphocytes, plasma cells, multinucleated giant cells, and neutrophils. Three of 8 cattle examined 6 or 8 weeks after inoculation had lesions in nonretropharyngeal sites with morphologic characteristics similar to that seen in retropharyngeal lymph node granulomas from cattle examined 4 weeks after inoculation. Conclusion Granulomas can develop in draining lymph nodes of cattle in as little as 4 weeks after inoculation via intratonsilar instillation of M bovis. Intralesional morphologic changes between 4 and 6 weeks after inoculation indicate an increase in cellular chemotaxis and differentiation. Dissemination of bacteria to distant sites most likely was by lymphatic and hematogenous routes after establishment of the primary infection in retropharyngeal lymph nodes. (Am J Vet Res 1999;60:310–315)

Incidence and patterns of retropharyngeal lymph node involvement in oropharyngeal carcinoma