Video Endoscopy-Guided Intrabronchial Spray Inoculation of Mycobacterium bovis in Goats and Comparative Assessment of Lung Lesions With Various Imaging Methods

Abstract

Bovine tuberculosis (bTB) not only poses a zoonotic threat to humans but also has a significant economic impact on livestock production in many areas of the world. Effective vaccines for humans, livestock, and wildlife are highly desirable to control tuberculosis. Suitable large animal models are indispensable for meaningful assessment of vaccine candidates. Here, we describe the refinement of an animal model for bTB in goats. Intrabronchial inoculation procedure via video-guided endoscopy in anesthetized animals, collection of lungs after intratracheal fixation in situ, and imaging of lungs by computed tomography (CT) were established in three goats using barium sulfate as surrogate inoculum. For subsequent infection experiments, four goats were infected with 4.7 × 102 colony-forming units of M. bovis by intrabronchial inoculation using video-guided endoscopy with spray catheters. Defined amounts of inoculum were deposited at five sites per lung. Four age-matched goats were mock-inoculated. None of the goats developed clinical signs until they were euthanized 5 months post infection, but simultaneous skin testing confirmed bTB infection in all goats inoculated with M. bovis. In tissues collected at necropsy, M. bovis was consistently re-isolated from granulomas in lymph nodes, draining the lungs of all the goats infected with M. bovis. Further dissemination was observed in one goat only. Pulmonary lesions were quantified by CT and digital 2D radiography (DR). CT revealed mineralized lesions in all the infected goats ranging from <5 mm to >10 mm in diameter. Small lesions <5 mm predominated. The DR failed to detect small lesions and to determine the exact location of lesions because of overlapping of pulmonary lobes. Relative volume of pulmonary lesions was low in three but high in one goat that also had extensive cavitation. CT lesions could be correlated to gross pathologic findings and histologic granuloma types in representative pulmonary lobes. In conclusion, video-guided intrabronchial inoculation with spray catheters, mimicking the natural way of infection, resulted in pulmonary infection of goats with M. bovis. CT, but not DR, presented as a highly sensitive method to quantify the extent of pulmonary lesions. This goat model of TB may serve as a model for testing TB vaccine efficacy.

Comparison of the pathological outcome and disease progression of two Mycobacterium caprae experimental challenge models in goats: endobronchial inoculation vs. intranasal nebulization

“…To date, different approaches to MTBC experimental infections have been modelized in goats: transthoracic (Bezos et al, 2010 , 2015 ), endobronchial (Pérez de Val et al, 2011 ; Wedlich et al, 2022 ), aerosolization (Gonzalez-Juarrero et al, 2013 ), and the infection by contact approach, i.e., the exposure of susceptible goats to infected ones by close contact (Bezos et al, 2017 ; Roy et al, 2019 ). The latter has the advantage to mimic natural infection in the herd but has the disadvantage of not controlling critical points such as the infection time point, infection dose, and infection route, which hinder the monitorization of the infection progress and, most critically, comparison between treatment groups.…”

“…However, cattle vaccination against TB is currently forbidden in the EU (Council Directive 78/52/EEC) due to interference with currently used TB diagnostic tools. The goat model of TB has proven to be a suitable one to study new TB vaccines for ruminants and humans and for a better understanding of the pathogenesis of the disease (Ramirez et al, 2003 ; Pérez de Val et al, 2011 , 2013 ; Wedlich et al, 2022 ).…”

Animal models for COVID-19 and tuberculosis

“…However, one report suggested that BCG has only a limited protective efficacy after challenge with M. caprae ( 259 ). More recent advanced goat models using video endoscopy for infection via intrabronchial spray inoculation ( 283 ) have demonstrated the relevance and suitability of goats for vaccine studies using BCG and new clinical candidates ( 284 , 285 ). Considering that BCG is the only licensed vaccine against TB it still remains the gold standard when testing new vaccine concepts.…”

Comparative pathology of experimental pulmonary tuberculosis in animal models

“…Goat TB closely resembles bovine and human TB in terms of immune response and pathological characteristics. They exhibit comparable patterns of disease progression, with a predominant anatomical localisation within the respiratory tract and the formation of caseous granulomas ( 77 , 107 ). In addition, goats demonstrate notable similarities in the anatomical structure of their respiratory tract, as well as a comparable size and body weight to that of humans ( 107 ).…”

“…They exhibit comparable patterns of disease progression, with a predominant anatomical localisation within the respiratory tract and the formation of caseous granulomas ( 77 , 107 ). In addition, goats demonstrate notable similarities in the anatomical structure of their respiratory tract, as well as a comparable size and body weight to that of humans ( 107 ). These shared features present a unique opportunity to bridge the gap between murine preclinical studies and subsequent human investigations ( 77 , 105 ), thereby providing valuable insights into the intricate mechanisms of host-mycobacteria interaction ( 77 ).…”