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EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2018) 30 (4) 172-176 doi: 10.1111/eve.12675


Case Report Tuberculosis caused by Mycobacterium bovis infection in a donkey


J. Bryan†*, P. den Boon‡, J. McGuirk§, G. Madigan§, R. Skuce# and U. Fogarty¶ †Veterinary Pathobiology, UCD School of Veterinary Medicine, University College Dublin; ‡The Donkey Sanctuary, Co. Cork; §Central Veterinary Research Laboratory, Backweston, Co. Kildare, Ireland; #Agrifood and Biosciences Institute, Queens University Belfast, UK; and ¶Irish Equine Centre, Naas, Ireland. *Corresponding author email: jill.bryan@ucd.ie


Keywords: horse; Mycobacterium bovis; tuberculosis; donkey; granulomatous pneumonia


Summary Mycobacterial infections are rare in equines. Mycobacterium bovis (M. bovis) is an important zoonotic bacterial pathogen causing disease in a wide range of animal species and sporadically causes severe disseminated disease in horses. This report describes the clinical, gross post-mortem examination and histopathological findings in a case of disseminated M. bovis infection in a donkey which to the authors’ knowledge has not been previously documented in the scientific literature.


Introduction


Naturally occurring mycobacterial infections are rare in horses, donkeys and mules; however, sporadic infections caused by the obligate pathogens Mycobacterium bovis (M. bovis) (Monreal et al. 2001; Keck et al. 2010) and Mycobacterium tuberculosis (O’Reilly and Daborn 1995; Pavlik et al. 2004) have been reported in horses. As well as these obligate pathogens, infection with environmental mycobacteria including Mycobacterium avium ssp. avium (Baker 1973; Mair et al. 1986; Buergelt et al. 1988; Lofstedt and Jakowski 1989; Cline et al. 1991), Mycobacterium terrae (Tasler and Hartley 1981), Mycobacterium smegmatis (Pavlik et al. 2004) and Mycobacterium holsaticum (Oaks 2007) have also been reported in horses, while suspected cases of Mycobacterium avium ssp. paratuberculosis infection and an uncharacterised mycobacterial infection have been reported in a donkey and mule, respectively (Kesten 1949; Dierckins et al. 1990). Mycobacteriumbovis, the cause of bovine tuberculosis, is an important zoonotic bacterial pathogen also responsible for disease in a wide range of other domestic and wild animal species (O’Reilly and Daborn 1995). In the past, disease caused by M. bovis was the most commonly reported mycobacterial infection of horses (Luke 1958; O’Reilly and Daborn 1995); however, in conjunction with the introduction of control programmes for M. bovis in other species, the incidence of infections in horses decreased in the second half of the last century (Pavlik et al. 2004) with only occasional cases being reported in the recent literature (Monreal et al. 2001; Keck et al. 2010). Although rare, M. bovis infection in horses has severe consequences as it is usually associated with disseminated disease resulting in death or euthanasia of the animal due to severe clinical disease, poor prognosis, or public health concerns.


Case details


History A 29-year-old donkey (Equus africanus asinus) gelding had been present on the current premises for the previous 4 years


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and was housed with approximately 40 other donkeys in a straw bedded barn with access to pasture during the spring and summer months. During this 4 year period the donkey did not have any direct contact with cattle. Four months previously the donkey had presented with acute onset soft tissue swelling of left and right carpal regions. General clinical examination at that time had revealed pain in both carpal regions and decreased range of motion of both carpal joints; however, there was no clinical evidence of respiratory disease. Radiographs of both carpi showed bilateral periarticular soft tissue swelling, while results of haematological and biochemical analysis were unremarkable. Based on the results of these diagnostic investigations the cause of the bilateral carpal swelling was thought to be due to localised cellulitis and responded well to empirical treatment with oxytetracycline (6.6 mg/kg bwt i.v. once a day [Engemycin 10%]1) and phenylbutazone (3 mg/kg bwt per os twice a day [Equipalizone]2). Subsequent to the episode of carpal swelling the donkey showed signs of progressive weight loss which began 4 weeks prior to being examined for acute onset tachypnoea. The donkey had no previous history of respiratory disease.


Clinical findings Four months after presentation for bilateral carpal swelling the donkey was examined by the same veterinarian for acute onset tachypnoea. Upon examination, the donkey was in moderate body condition (body condition score 2.5/5 [Smith and Wood 2008]) but appeared lethargic. Rectal temperature was elevated (38.6°C), heart rate was increased with a rate of 60 beats/min, respiratory rate was increased with a rate of 40 breaths/min and there was increased respiratory effort. Mucous membranes appeared pale pink and moist with a capillary refill time of <2 s. Thoracic auscultation revealed bilateral, generalised inspiratory and expiratory musical wheezes and areas of crackles. On abdominal auscultation there was decreased intensity of intestinal sounds. Haematological examination identified leucocytosis (27.21 9 109/L; reference range 6.1–16.1 9 109/L) with neutrophilia (17.76 9 109/L; reference range 2.2– 13.3 9 109/L) and monocytosis (1.65 9 109/L; reference range 0–0.8 9 109/L), while results of serum biochemistry analysis were unremarkable. Based on the history, physical examination and laboratory findings, in particular the acute onset of disease, tachypnoea, increased respiratory effort, abnormal sounds on thoracic auscultation and the presence of a leucocytosis with neutrophilia, an infectious bronchopneumonia was considered to be the most likely differential diagnosis. Concurrent idiopathic pulmonary fibrosis was also considered to be a

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