Case A
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History
A three week old piglet with a history of diarrhoea.
Example histopathological description
The specimen is a complete transverse section of small intestine. There is severe diffuse stunting of villi and much of the superficial mucosal epithelium is attenuated, often with a cuboidal or occasionally squamous appearance. Areas of epithelial attenuation alternate with foci of epithelial hyperplasia. Scattered small foci of epithelial erosion are present. Many epithelial cells on the surface of villus remnants contain intracytoplasmic organisms which resemble type I merozoites of Isospora spp. The organisms are 4-5 x 12-14 µm in size and are often in pairs. Occasional cells contain type II meronts or microgamonts. The lamina propria is diffusely expanded with a moderate infiltrate of lymphocytes, plasma cells, macrophages and eosinophils. Crypt epithelium is diffusely hyperplastic with frequent mitotic figures evident. The submucosa is moderately infiltrated with eosinophils and macrophages and there is abundant hyperplastic, submucosal follicular lymphoid tissue.
Morphological diagnosis:
Enteritis; lymphocytic, plasmacytic and eosinophilic; chronic, diffuse, severe, with marked diffuse villus atrophy and large numbers of intralesional coccidians.
Aetiological diagnosis:
Coccidial enteritis; presumptively Cystoisopora suis (syn. Isospora suis)
Case B
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History
A Spectacled Flying Fox with a history of neurological signs.
Example histopathological description
The section of brain is one-half of a complete transverse section at the level of the diencephalon, including the thalamus and hippocampus. In both the white and grey matter there is moderate generalised multifocal gliosis, primarily involving oligodendrocytes and microglia, with satellitosis of some intralesional neurons and rarefaction of the affected parenchyma. Within foci, and in moderate numbers scattered throughout the neuropil, there are shrunken dark neurons, although in some areas this change is likely to be artifact. The meninges are regionally thickened by amorphous eosinophilic material (likely fibrin) and low numbers of lymphocytes, plasma cells and macrophages. A moderate amount of similar inflammatory exudate is present within the third ventricle. The choroid plexus and meninges have generalised vascular congestion and mild acute haemorrhage. Primarily in the cerebral cortex, both associated with foci of necrosis and in unaffected parenchyma, there are low numbers of 20-30 µm diameter round structures, with fine internal darker punctate appearance, suggestive of apicomplexan protozoa tissue cysts.
Morphological diagnoses
Encephalitis; non-suppurative, chronic, multifocal, moderate, with intralesional protozoa.
Adrenalitis; necrotising, subacute to chronic, multi-focal to diffuse, severe, with intralesional protozoa.
Aetiological diagnosis:
Protozoal encephalitis, with the most likely aetiology being Toxoplasma gondii. The most important differential diagnosis is Australian bat lyssavirus infection.