EQUINE VETERINARY EDUCATION / AE / APRIL 2018


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possibility as this was a relatively common post-mortem finding in other donkeys from this premises. Further diagnostic investigations including thoracic ultrasonography, thoracic radiography and a transtracheal wash were considered to try to establish a more definitive diagnosis; however, given the degree of tachypnoea and potential stress to a donkey with


respiratory compromise, it was decided to initiate treatment first and reconsider additional diagnostics at a later stage.


Treatment and outcome Empirical treatment based on the presumptive diagnosis of infectious bronchopneumonia was initiated with the administration of intravenous flunixin meglumine (1.1 mg/kg bwt twice a day [Finadyne]1), trimethoprim sulfadiazine (15 mg/kg bwt once a day [Norodine 24%]3) and clenbuterol (0.8 lg/kg bwt twice a day [Ventipulmin injection solution]4); however, response to initial treatment was poor and repeated physical examinations carried out every 2 h showed that the donkey remained lethargic, tachypnoeic, tachycardic and pyrexic with a severely increased respiratory effort and progressively worsening lung sounds. Based on this poor response to initial treatment, poor prognosis, continued rapid clinical deterioration and also considering the advanced age of the animal it was decided that the donkey should be subjected to euthanasia 24 h after the start of treatment.


Gross post-mortem findings On gross post-mortem examination the donkey was in moderate body condition. Examination of the lungs indicated diffuse consolidation with an irregular nodular appearance of the surface in many areas and multiple coalescing, firm, pale masses diffusely distributed throughout the parenchyma (Fig 1). The cranioventral region of the right caudal lung lobe contained multifocal areas of necrosis and the bronchial and mediastinal lymph nodes appeared enlarged. Multiple, variably sized, firm, pale nodular masses were identified within the mediastinal space associated with the aorta and ventral aspect of thoracic vertebrae (Fig 2) and a similar focal mass, 5 mm in diameter, was present on the epicardial surface. Within the abdomen, multifocal, firm, pale, smooth surfaced nodules ranging from 1 to 10 mm in diameter were identified on the surface of the liver, spleen and diaphragm and within the omentum and cortices of both kidneys. On cross section these nodules appeared uniformly pale and firm. The mesenteric and colonic lymph nodes were enlarged.


Histopathological findings Histopathological examination of lung tissue showed effacement of normal lung architecture with prominent interstitial and subpleural fibrosis and a diffuse, severe mixed inflammatory cell infiltration composed predominantly of macrophages and lymphocytes with occasional multinucleated giant cells, consistent with granulomatous inflammation (Fig 3). In multiple sections of lung the inflammatory infiltrate was organised to form variably sized discrete granulomas characterised by fibrous tissue surrounding aggregates of macrophages, varying numbers of lymphocytes and occasional multinucleated giant cells (Fig 4). A small number of granulomas had central areas of necrosis and acid fast bacilli were identified within these areas (Fig 4 inset). Histopathologically, the masses from the mediastinal space, epicardium, kidney, liver, spleen,


Fig 1: Multiple coalescing masses diffusely distributed throughout the lung parenchyma and causing an irregular nodular appearance of the surface in many areas.


Fig 2: Multiple nodular masses within the mediastinal space (arrows).


diaphragm and omentum were composed of fibrous tissue surrounding aggregates of macrophages and lymphocytes with some multinucleated giant cells, consistent with chronic granulomatous inflammation. However, no acid fast bacilli were identified within these lesions.


Microbiological findings Routine bacterial culture of lung tissue under aerobic and anaerobic conditions isolated a moderate growth of b- haemolytic streptococci as well as light growths of a- haemolytic streptococci and Escherichia coli. Based on the gross post-mortem findings, mycobacterial infection was considered a possibility and lung tissue was also submitted for mycobacterial culture. After processing by standard methods, extracts from lung tissue were inoculated onto Lowenstein-Jensen medium with pyruvate, Stonebrink’s medium and into a Bactec MGIT 960 tube. Cultures were incubated at 37°C. The Bactec MGIT signalled positive after 5 days indicating the presence of mycobacteria and a Ziehl- Neelsen stain carried out showed corded acid fast bacilli.


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