A review of infection of wildlife hosts with Mycobacterium bovis and the diagnostic difficulties of the ‘no visible lesion’ presentation

Abstract

The pathology, frequency and diagnostic implications of ‘no visible lesion’ (NVL) tuberculosis (Tb), i.e. infection with Mycobacterium bovis in the absence of macroscopic lesions, are described in a wide taxonomic range of wildlife hosts. Information collected and evaluated on the definition and occurrence of NVL Tb, histopathological characteristics, post-mortem techniques to detect minimal lesions, and diagnostic difficulties revealed most Tb-infected individuals with NVL had minute tuberculous lesions, which were difficult to see by eye. Acidfast organisms (AFO) were sometimes detected in the lesions. Ideally, mycobacterial culture of pools of lymph nodes and/or oropharyngeal tonsils is necessary for the accurate diagnosis of Tb in the absence of macroscopic lesions. At a very minimum, the diagnostic methods applied for studying the prevalence of Tb in the population should be clearly described, to allow comparison between studies.

KEY WORDS::

• Bovine tuberculosis
• Mycobacterium bovis
• wildlife
• Eurasian badger (Meles meles)
• brushtail possum (Trichosurus vulpecula)
• cervids
• ferrets (Mustela furo)
• European wild boar (Sus scrofa)

Acknowledgements

The authors acknowledge financial support from Santander and Fundación Marcelino Botín, and the Department for Environment, Food and Rural Affairs, UK. The advice and input of TR Crawshaw, Veterinary Laboratories Agency, and LAL Corner and S Gordon, University College Dublin, Ireland, are gratefully acknowledged. We thank Maria Paz Martín-Hernando for Figures 5, 6, 7 and 8.