Atypical granuloma formation in Mycobacterium bovis-infected calves

Abstract

Bovine tuberculosis is a chronic inflammatory disease that causes granuloma formation. Characterization of granulomatous lesions of Mycobacterium bovis ( M . bovis) experimentally infected cattle has helped to better understand the pathogenesis of this disease. However, few studies have described granulomas found in M . bovis naturally infected cattle. The aim of this work was to examine granulomas from Holstein-Friesian cattle naturally infected with M . bovis from a dairy basin located in the central region of Mexico. Tissue samples from thirty-two cattle with lesions suggestive of tuberculosis were collected post-mortem. Fifteen of the 32 sampled animals (46.8%) were 4 months of age or younger (calves), whereas the rest (53.2%, 17/32) were over one year old (adults). Macroscopic lesions suggestive of tuberculosis were found in the mediastinal lymph node chain of all animals (32/32). From the 1,143 granulomatous lesions that were microscopically analyzed, 34.6% (396/1143) were collected from adult animals and subsequently classified according to the nomenclature suggested by Wangoo et al ., 2005. Surprisingly, lesions from calf tissues showed an atypical pattern which could not be fitted into the established developmental stages of this classification. Granulomatous lesions found in calves covered most of the affected organ, histologically showed large necrotic areas with central calcification, absence of a connective tissue capsule, and few giant cells. Also, there was a higher percentage of lesions with acid-fast bacilli (AFB) when compared to studied granulomas in adults. Growth of Mycobacterium spp was detected in 11 bacteriological tissue cultures. Genotypic identification of M . bovis was performed by DNA extraction from bacterial isolates, formalin-fixed and paraffin-embedded (FFPE) tissues and samples without bacterial isolation. M . bovis was detected by PCR in 84.3% (27/32) of the studied cases; whereas other AFB were observed in tissues of the remaining sampled animals (5/32). Our results describe atypical granuloma formation in calves 4 months of age or younger, naturally infected with M . bovis . These findings contribute to better understanding the physiopathology of M . bovis infection in cattle.

Animal tuberculosis: impact of disease heterogeneity in transmission, diagnosis, and control

“…The cellular immune response impacts granuloma's development and evolution to disease confinement or dissemination. Observation of granulomas in different developed stages within the same organ of M. bovis naturally infected cattle has been reported (Carrisoza‐Urbina et al, 2019), which reveals the presence of different immune microenvironments.…”

“…In an initial phase (stage I), granulomas are formed by irregular unencapsulated clusters of epithelioid macrophages and lymphocytes of the B and T type; then, evolving to clusters with a thin capsule and necrotic areas (stage II); further to encapsulated granulomas with central necrosis and mineralized areas (stage III); and finally, to thickly encapsulated multicentric granulomas, with prominent caseous necrosis and extensive islands of mineralization (stage IV; Wangoo et al, 2005). However, in a work performed by Carrisoza‐Urbina, Morales‐Salinas, Bedolla‐Alva, Hernández‐Pando, and Gutiérrez‐Pabello (2019) with M. bovis naturally infected cattle, the granulomatous lesions of calves revealed an atypical pattern, not fitting into the previously established classification defined by Wangoo et al (2005). These granulomas lacked a fibrous capsule, and the classification of their formation was adapted to stages I, II, II–III and III–IV (Carrisoza‐Urbina et al, 2019).…”

“…However, in a work performed by Carrisoza‐Urbina, Morales‐Salinas, Bedolla‐Alva, Hernández‐Pando, and Gutiérrez‐Pabello (2019) with M. bovis naturally infected cattle, the granulomatous lesions of calves revealed an atypical pattern, not fitting into the previously established classification defined by Wangoo et al (2005). These granulomas lacked a fibrous capsule, and the classification of their formation was adapted to stages I, II, II–III and III–IV (Carrisoza‐Urbina et al, 2019).…”

Cell-Mediated Immunological Biomarkers and Their Diagnostic Application in Livestock and Wildlife Infected With Mycobacterium bovis

“…The hallmark lesion of bTB in cattle is the granuloma that can be found in the lung, lymph nodes and potentially other organs ( 62 ). Granuloma stages have been well-described in cattle and are based on morphological characteristics, i.e., degree of necrosis and mineralization, and presence of a connective tissue capsule ( 63 ). However, M. bovis disease development and pathological lesions can vary widely between species, with cavitary pulmonary lesions instead of granulomas in goats and gastrointestinal infection observed in predators, for example lions ( 64 – 66 ).…”

“…However, correlations between IFN - γ and M. bovis pathology have been preliminarily detected in badgers and buffaloes ( 72 , 74 ). Moreover, investigating the associations between cytokine responses at both a gene and protein level, alongside host-specific pathological changes, can provide more insight on the diagnostic potential of IFN - γ and additional biomarkers ( 5 , 63 , 75 , 94 , 123 , 124 ).…”