Effects of experimental m. Microti infection on the health and diagnosis of tuberculosis in goats
Tuberculosis (TB) is an infectious disease caused by bacteria in the Mycobacterium tuberculosis complex (MTBC). M. bovis, M. caprae and M. tuberculosis are the main causes of TB in mammals. M. microti has been described as a pathogen affecting wild voles and other species, including immunocompromised humans.
This study evaluated the effects of M. microti infection on TB diagnosis in goats and characterized its pathogenesis. Goats were divided into 5 groups and infected with M. microti by different routes. Goats were monitored weekly by taking temperature, weighting, and observing them for clinical signs of the disease, blood samples were also taken weekly until the end of the experiment. Post euthanasia, the corresponding postmortem tests were carried out. An outline of the experimental design is shown below:
The main results were:
Exposure to a high dose of M. microti by endobronchial high dose (EB-HD) route resulted in subclinical lung infection in all goats. One goat in the SC (subcutaneous) group developed subclinical infection. No infection was detected in the EB-LD (low dose endobronchial), PO (oral) and IN (intranasal) groups.
Two goats (EB-HD and SC) showed positive tuberculin skin test results. Two other goats (EB-HD and EB-LD) showed equivocal results. No positive reactions were observed with specific antigens absent in M. microti (ESAT-6 and CPF-10).
Histopathological results showed lesions compatible with tuberculosis in three animals (EB-HD, EB-LD, and SC groups). BAAR was observed within one lung lesion (EB-HD). Mycobacterium isolation was achieved by culture (4 animals from the EB-HD group and 1 animal from the SC group).
Our results indicate that animals exposed to M. microti can give positive results in skin tests currently performed in tuberculosis eradication campaigns in cattle and reinforce the need to use specific antigens in ante mortem tests to avoid interference with M. bovis/M. caprae
The study was funded by grants from the Interreg POCTEFA 2004-2020 programme of the European Commission (EFA357/INNOTUB, co-funded by FEDER) and the Spanish State Research Agency (PID2019-105155RB-C32/AEI/10.13039/501100011033). IRTA is supported by the CERCA Programme / Generalitat de Catalunya.
Melgarejo, C., Cobos, À., Domingo, M., Cantero, G., Moll, X., Sevilla, I. A., Garrido, J. M., Michelet, L., Boschiroli, M., Vidal, E., & De Val, B. P. (2024). Experimental infection of goats with Mycobacterium microti induces subclinical pulmonary tuberculosis and mild responses to tuberculin skin tests. Veterinary Microbiology, 290, 110009. https://doi.org/10.1016/j.vetmic.2024.110009
