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with confirmation by PCR and reverse hybridisation. The extrapulmonary lesions were assumed to be caused by the same aetiological agent based on the histopathological appearance; however, acid-fast bacilli were not identified in these lesions. It is recognised that the numbers of acid-fast bacteria visualised microscopically within lesions caused by M. bovis frequently do not reflect the mycobacterial load as determined by culture (Cassidy 2006). McCune and Tompsett (1956) found that acid-fast bacteria could not be detected with certainty microscopically when mycobacterial numbers were less than 105 colony forming units per ml of tissue and this highlights the importance of culture in identifying mycobacterial infections in horses and donkeys. The route of infection for M. bovis in horses is often


assumed to be ingestion (O’Reilly and Daborn 1995; Pavlik et al. 2004; Keck et al. 2010). In the current case intestinal lesions were not identified; however, mesenteric and colonic lymph nodes were enlarged and it is possible that infection occurred via ingestion without evidence of intestinal lesions. Inhalation is an important route of infection in cattle and man (O’Reilly and Daborn 1995; de la Rua-Domenech 2006) and infection via this route could also be possible in equines (Keck et al. 2010). Since 1954, Ireland has had a national programme for the eradication of bovine tuberculosis; however, in some regions, M. bovis infection still causes disease in cows, and badgers are considered to be an important wildlife reservoir (Sheridan 2011). Contact with infected cattle has previously been identified as a source of infection for a horse with M. bovis tuberculosis (Keck et al. 2010). Possible sources of infection in the current case remain speculative. The donkey did not have contact with cattle during the previous 4 years and during this time it was kept in an area of the country which is considered to be low risk for M. bovis infection in cattle. Also, there has been no evidence to support a diagnosis of M. bovis infection in any other donkey housed on the same premises either previous or subsequent to the current case. However, the donkey’s history prior to this period included a number of years in an area of the country considered high risk for tuberculosis. In human medicine, recrudescence of long-standing latent infections are considered an important cause of clinical cases of M. bovis tuberculosis in people in developed countries (de la Rua-Domenech 2006) and a similar pathogenesis could occur in equines. In this case spoligotyping was carried out to determine the molecular type of the isolated M. bovis. Molecular types of M. bovis tend to be highly geographically localised and can therefore give an indication of likely geographical location at the time of infection. The spoligotype SB0140 identified in this case is the spoligotype most frequently identified in M. bovis isolates in Ireland (McLernon et al. 2010) and does not give any indication of probable geographic location of the donkey at the time of infection. M. bovis is a zoonotic organism that can cause infection


in people through ingestion, inhalation or, less frequently, by contact with mucous membranes or broken skin (de la Rua- Domenech 2006). There appear to be no published reports of M. bovis infection in man attributable to infection acquired from equines; however, horses and donkeys are companion animals and remain a possible source of infection for people. In the current case, veterinary and farm staff that had been in close contact with the infected donkey were screened for exposure to M. bovis with all results negative for M. bovis infection.


In conclusion, although infection is rare in equines,


mycobacterial disease caused by M. bovis should be considered as a possible differential diagnosis in donkeys presenting with signs of lower respiratory disease. Although clinical signs are generally nonspecific, submission of samples for mycobacterial culture may be warranted as part of the diagnostic evaluation, particularly in cases where there is evidence of respiratory or generalised granulomatous inflammation or in geographical areas where the disease is prevalent in other domestic species or the wildlife population.


Authors’ declaration of interests No conflicts of interest have been declared.


Ethical animal research Not applicable to this case report.


Source of funding None.


Acknowledgements


The authors thank The Donkey Sanctuary, Sidmouth for permission to publish this case report and all the staff involved in the collection and handling of samples. The authors would also like to thank B. Cloak for assistance with photomicroscopy.


Authorship


J. Bryan reviewed the histological slides and prepared the manuscript. P. den Boon provided clinical care and was involved in writing the clinical section of the manuscript. J. McGuirk, G. Madigan and R. Skuce carried out microbiological analysis, interpretation and writing of the relevant sections. U. Fogarty carried out the gross post- mortem and histopathological examination and was involved in writing the pathology sections of the manuscript. All authors approved the final manuscript.


Manufacturers' addresses


1MSD Animal Health, Dublin, Ireland. 2Dechra Veterinary Products, Stoke on Trent, UK. 3Norbrook Laboratories Limited, Newry, Northern Ireland. 4Boehringer Ingelheim Vetmedica, Berkshire, UK. 5Hain Lifescience GmbH, Nehren, Germany.


References


Baker, J.R. (1973) A case of generalised avian tuberculosis in a horse. Vet. Rec. 93, 105-106.


Buergelt, C.D., Green, S.L., Mayhew, I.G., Wilson, J.H. and Merritt, A.M. (1988) Avian mycobacteriosis in three horses. Cornell. Vet. 78, 365- 380.


Cassidy, J.P. (2006) The pathogenesis and pathology of bovine tuberculosis with insights from studies of tuberculosis in humans and laboratoy animal models. Vet. Microbiol. 112, 151-161.


Caswell, J.L. and Williams, K.J. (2007) Respiratory system. In: Jubb, Kennedy and Palmer’s Pathology of Domestic Animals, 5th edn., Vol. 2, Ed: M. Grant, Maxie Elsevier Limited, Philadelphia. pp 609- 610.


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