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studies have concluded that hyperammonaemia is not consistently a feature of HE (McGorum et al. 1999; Durham et al. 2003a,b) and serum ammonia is not accurately measurable in the general practice setting due to sample degeneration in transport. It is likely that hepatic fibrosis and inflammatory infiltrates as a result of extensive hepatic infiltration with bTB resulted in impaired liver function in this case, possibly resulting in concomitant signs of HE. Subsequent reduced efficiency of protein synthesis and conversion likely resulted in weight loss and reduced albumin concentrations. Weight loss and intermittent pyrexia are well-documented


signs of bTB in multiple species (O’Reilly and Daborn 1995). This is presumably on the basis of negative energy balance due to reduced appetite and part of a systemic inflammatory response syndrome (Van Creval et al. 2002). This is supported in this case by the inflammatory leucogram and hyperglobulinaemia. In addition, weight loss may have been a feature of PPID associated catabolism. Pleural rubs and tachypnoea were likely present due to severe, necrotising, granulomatous pneumonia identified on histopathology associated with bTB microgranulomas and, less so, space occupying Echinococcus cysts. Exacerbation of a previously hypersensitive airway (recurrent airway obstruction history) due to systemic inflammatory response syndrome might also have contributed (Papi et al. 2006). In addition, bronchointerstitial inflammation and bronchiolitis have been identified in PPID affected equids at post-mortem examination (Glover et al. 2009). It is hypothesised this is a consequence of the generalised inflammatory dysregulation that occurs in PPID and may be an additional contributing factor in this case.


Mycobacterial infection in equids The mode of transmission of mycobacterial infections in horses is unclear (M€


onki et al. 2016). An oral route of infection in


equids is most likely (Pavlik et al. 2008) with subsequent haematogenous spread accountable for the diversity of organotropisms. Environmental contamination can occur through deposition of secretions from infective hosts or carcasses including sputum, excrement and purulent material (P


erez-Lago et al. 2014). A known history of bTB infected cattle


on the adjacent farm was reported by the owner. This may represent a long-standing potential source of environmental


infection. Clinical history and post-mortem examination findings in this case indicated a chronic state of infection. bTB can be a slow, insidious disease and remain dormant for many years (O’Reilly and Daborn 1995), the precise time of infection therefore remains uncertain. It is plausible that initial exposure may have occurred many years previously. In man, immune suppression is regarded a prerequisite for


clinical disease (Xu et al. 2014). Opportunistic or secondary infections occur in approximately 35% (63 of 180) of horses with PPID compared with 11% (4 of 33) of healthy aged horses (Glover 2009). Consequently, the possibility of a predisposition to Echinococcus and bTB secondary to PPID cannot be ruled out in this case. Other reports have not described mycobacterial disease with concurrent PPID.


Echinococcus Echinococcus cysts are frequently identified at necropsy in clinically normal equids. Large echinococcus cysts have been implicated as a possible cause of clinical hepatic disease due to compression and expansion within tissue (Sellon and Long


2013); however, Echinococcus cysts are unlikely to have been the cause of significant hepatic compromise in this case. No previous reports describe Echinococcus in conjunction with equine TB and these findings are probably unrelated. The intrinsic immunity of individual horses influences the extent of parasite burdens. Equids with PPID have been shown to have higher faecal egg counts, suggesting that they could be more susceptible to endoparasitism (McFarlane 2011), potentially explaining the presence of multiple Echinococcus cysts in this case.


Public health and professional relevance Mycobacterium bovis represents a known risk to public health and huge financial and logistic resources are dedicated to monitoring and eradication programmes. Consequently, people working in the agricultural and animal health sectors, including veterinarians are at an increased exposure risk. A case study in 2010 produced by the University of Bern described mycobacterial infection in three vets following necropsy of an infected dog, clearly highlighting the importance of disease awareness (Posthaus et al. 2011). At this establishment, a new protocol for assessing risk of zoonotic disease prior to necropsy has been installed to help mitigate risk to personnel. The wearing of gloves and face masks to cover the eyes and nose should be a compulsory component of post-mortem examination to minimise potential exposure to infectious organisms (Whitwell 2009). In the UK all suspected cases of TB should be reported to The Animal and Plant Health Agency (APHA). The APHA recommends potentially exposed individuals undertake an infection-risk questionnaire via telephone with the local APHA office. Testing blood or intra dermal testing of exposed individuals is advised and funded by the APHA on a relative-risk basis taking into account factors such as age, degree and chronicity of exposure, vaccination status and presence of other illnesses. Suspected infectious samples (containing acid fast


bacteria), should be submitted for species subtyping by PCR to assist in TB species monitoring in the UK. Mycobacterial PCR can be performed at Cardiff, Edinburgh and Leeds teaching hospitals. The treating vet in this case underwent mycobacterial antibody serology as deemed appropriate by the APHA and tested negative. The pony’s owner and her husband underwent intradermal skin testing that indicated exposure. Subsequent antibody serology was negative. Advice relating to appropriate biosecurity measures in


terms of other horses is lacking and given the low risk propensity of TB infection in equids if cohorts appear clinically normal and in good body condition, then a disease free state can probably be assumed.


Author’s declaration of interests No conflicts of interest have been declared.


Ethical animal research


No ethical review. Report of case treated at Peasebrook Equine Clinic.


Source of funding Private funding: Dr Danielle Gunn-Moore, University of Edinburgh, Feline Mycobacteria specialist. Funding of PCR


© 2017 EVJ Ltd


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