Different lesion distribution in calves orally or intratracheally challenged with Mycobacterium bovis: implications for diagnosis

Miriam Serrano,Maria Ángeles Risalde,Natalia Elguezabal,Christian Gortazar,Iker A Sevilla,Lucas Domínguez,Mariví Geijo,Jose Francisco Ruiz-Fons,Ramón A Juste,Miguel Fuertes,Joseba M Garrido

doi:10.1186/s13567-018-0566-2

Abstract

Animal tuberculosis (TB) remains a major problem in some countries despite the existence of control programmes focused mainly on cattle. In this species, aerogenous transmission is accepted as the most frequent infection route, affecting mainly the respiratory system. Under the hypothesis that the oral route could be playing a more relevant role in transmission, diagnosis and disease persistence than previously thought, this study was performed to assess the course of TB infection in cattle and its effects on diagnosis depending on the route of entry of Mycobacterium bovis. Two groups of five calves each were either endotracheally (EC) or orally (OC) challenged. Necropsies were carried out 12 weeks after challenge except for three OC calves slaughtered 8 weeks later. All animals reacted to the tuberculin skin test and the entire EC group was positive to the interferon-gamma release assay (IGRA) 2 weeks after challenge and thereafter. The first positive IGRA results for OC calves (3/5) were recorded 4 weeks after challenge. Group comparison revealed significant differences in lesion and positive culture location and scoring. TB-compatible gross lesions and positive cultures were more frequently found in the thorax (p < 0.001) and lung (p < 0.05) of EC animals, whereas OC animals presented lesions (p = 0.23) and positive cultures (p < 0.05) mainly located in the abdomen. These results indicate that the infection route seems to be a determining factor for both the distribution and the time needed for the development of visible lesions. Our study suggests that confirmation of TB infection in some skin reactor animals can be problematic if current post-mortem examination and diagnostics are not improved.

Highlights

Mycobacterium bovis is the main etiological agent of animal tuberculosis (TB), a mycobacterial infectious disease with a worldwide distribution [1] that affects cattle [2], other domestic hosts [3], wildlife [4] and humans [5]
There is a general acceptance that the aerogenous transmission is the most frequent one in cattle and lesions are usually found in the respiratory system and associated lymph nodes (LN) [17, 18]
Animal selection This project was aimed at studying the interference of paratuberculosis vaccination on TB diagnosis [32, 33], the effect of M. bovis inoculation route on the pathology and diagnostics of bovine TB and the efficacy of an inactivated vaccine to protect them from oral and endotracheal challenge with M. bovis

Summary

Introduction

Mycobacterium bovis is the main etiological agent of animal tuberculosis (TB), a mycobacterial infectious disease with a worldwide distribution [1] that affects cattle [2], other domestic hosts [3], wildlife [4] and humans [5]. There is a general acceptance that the aerogenous transmission is the most frequent one in cattle and lesions are usually found in the respiratory system and associated lymph nodes (LN) [17, 18] This seems to be the case for natural intra-species transmission in the badger, the principal wild animal reservoir in Ireland and UK [20]. In the wildlife-livestock interface inter-species transmission is of an indirect nature, for instance through shared water or food [22, 23]. In these cases, infection will most likely enter the host by the oral route. Widespread contamination of environmental samples in the Iberian Peninsula suggests that indirect transmission contributes to the maintenance of tuberculosis in multi-host–pathogen systems [24, 25]

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