192


EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2018) 30 (4) 192-196 doi: 10.1111/eve.12786


Case Report


Multisystemic bovine mycobacteriosis in a pony with neurological signs and weight loss


V. Charlesworth Hambleton Equine Clinic, Middlesbrough, UK. Corresponding author email: victoria.charlesworth@hambleton-equine.co.uk


Keywords: horse; mycobacteria; tuberculosis; hepatitis


Summary This report describes the clinical, biochemical and histopathological findings of a case of disseminated, primary mycobacterial infection with Mycobacterium bovis in a pony presenting with neurological signs and weight loss. This report revisits tuberculosis as a potential differential diagnosis in horses at a time of relatively strong tuberculosis control in the UK and iterates the importance of post-mortem examination as a diagnostic tool for clinicians. Key public health questions following exposure to mycobacterial pathogens are also discussed.


Introduction


Mycobacterium bovis (bTB) is a mycobacterium of the tuberculosis (TB) complex. M. bovis can affect a wide host range including cattle and other ruminants, people, horses, badgers, cats, and dogs. The infection is notifiable due to its zoonotic potential. Under high infection pressure, transmission occurs by respiration of aerosolised bacteria (O’Reilly and Daborn 1995), or by ingestion (Pavlik et al. 2004). Interspecies transmission between dead end hosts such as dogs, cats and people, amongst others, is reported but not well understood (De la Rua-Domenech 2005). Equine TB is rarely reported as a primary cause of disease in horses (Pavlik et al. 2008) probably due to a natural high resistance to infection (Anzai et al. 1989; Gunnes et al. 1995). Improved biosecurity of production animals in the UK has reduced the exposure of equids to mycobacterial pathogens (Mair et al. 1986). Current prevalence data relating to equine TB are lacking. In old reports, the incidence of granulomatous tubercles was 0.3% of 124 horses slaughtered in Germany (Schutzler 1954) and 2.3% of 214 horses in the Czech Republic (Krejci 1958). A shift between TB subtypes has been observed. ‘Test and cull’ strategies on cattle farms have probably reduced the dominance of bTB (Mair et al. 1986; Pavlik et al. 2004) leading to the increasing diagnosis of Mycobacterium avium complex (MAC) pathogens amongst equids. Clinical signs of disease in equids relate to the duration and location of infection (Mair et al. 1986). Mostly lung, spleen and liver are involved; however, intrasynovial, ocular and cervical abscesses have also been reported (Verge and Senthille 1942; Krejci 1958; Pavlik et al. 2004). Definitive confirmation of disease is challenging since acid-fast bacteria are not always detected in submitted samples. The intradermal tuberculin test is considered unreliable in terms of sensitivity and specificity in horses (Pavlik et al. 2004; Keck et al. 2010). This report aims to highlight bTB as a rare, potential equine pathogen and describes the clinical and histopathological


© 2017 EVJ Ltd


features of this UK case. Public health issues relating to bTB diagnosis are also discussed.


Case report


History A 23-year-old Fell pony gelding presented for weight loss with recent onset depression. Weight loss was noted over the last 6 months. During this period, the pony had one known occurrence of pyrexia (39.8°C) with no haematological abnormalities. Pyrexia had been treated with flunixin meglumine, (1.1 mg/kg bwt i.v.) by the attending veterinarian. Historically, moderate signs of presumed equine asthma (recurrent airway obstruction) had been observed, although this was not considered a recent problem. A routine faecal worm egg count 4 weeks prior to presentation was negative. The pony was retired and turned out at grass with free access to stables located within 100 m proximity to an active beef farm.


Clinical findings On presentation, the pony was markedly depressed with a body condition score of 2/9 (Henneke et al. 1983). Hypersalivation, marked abdominal distension and atrophy of epaxial and postural musculature were noted. Clinical examination revealed a heart rate of 52 beats/


min, a respiratory rate of 20 breaths/min and a rectal temperature of 38.5°C. Oral inspection showed hyperaemic mucous membranes with some ulceration in proximity to the incisors. There was some uneven tooth wear but no other dental abnormalities were noted. On auscultation of the lungs increased bronchovesicular sounds were audible bilaterally with occasional pleural rubs over the right hemithorax. Weakness and ataxia were evidenced by swaying at rest and the pony displayed a plaiting unsteady gait. No abnormalities were detected on cranial nerve evaluation.


Haematology revealed a moderate leucocytosis


(15 9 109/L, reference range [rr]: 5.40–14.30 9 109/L) and neutrophilia (13.75 9 109/L, rr: 2.26–8.50 9 109/L). Biochemistry revealed marked hyperproteinaemia (89 g/L, rr: 56–79 g/L), hyperglobulinaemia (64 g/L, rr: 24–47 g/L) and mild hypoalbuminaemia (25 g/L, rr: 29–41 g/L). Alkaline phosphatase (729 u/L, rr: 10–326 u/L), c-glutamyl transferase (412 u/L, ref: 0–87 u/L) and lactate dehydrogenase (2095 u/L, rr: 250–460 u/L) activities were all elevated. Testing for pituitary pars intermedia dysfunction (PPID) revealed an elevated adrenocorticotrophic hormone concentration of 42 pg/mL (rr: <29 pg/mL seasonally adjusted range).


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80