Case A
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History
10 day old replacement layer chicks with neurological signs and increased mortalities.
Example histopathological description
This is a parasagittal section of the brain which includes the brainstem, cerebellum and cerebrum. There are two discrete, sharply demarcated, focal areas of malacia, the larger in the rostral medulla and the smaller in the ventral forebrain. Within these foci the pale vacuolated neuropil contains acutely necrotic neurones and glia. Some capillaries in and around the foci are dilated, have necrotic endothelial cells, fibrin and additional cells, indicating thrombosis. In the cerebellum, some Purkinje cells are hypereosinophilic, shrunken and angular, with loss of nuclear detail, suggesting acute necrosis.
Morphological diagnosis
Encephalomalacia, multifocal, acute, severe, with capillary thrombosis.
Differential diagnosis
1. Enterococcal encephalomalacia (Enterococcus durans was isolated from the brain and spleen)
2. Nutritional encephalomalacia (hypovitaminosis E)
Case B
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History
Guinea fowl with chronic ill-thrift
Example histopathological description
This is a longitudinal section that includes the distal oesophagus and the proximal proventriculus. There are separate and distinct lesions in each anatomical location.
The oesophageal mucosa is markedly and diffusely thickened and irregular as a result of exuberant squamous hyperplasia. Embedded within this lesion, which extends to the oesophageal-proventricular junction, there are numerous adult nematodes with cross-sectional diameters of 100-200µm. The parasites have two cords of coelomyarian musculature and two bacillary bands. There are abundant, ellipsoid, 15 µm x 35 µm eggs, with bipolar plugs, in and around some nematodes suggesting the parasites are probably Capillaria sp. Also present on both the epithelial surface and deep within pockets of hyperplastic epithelium are clusters of round to pear-shaped flagellate protozoa, 5-6µm in diameter, consistent with Trichomonas sp. Mild to moderate lymphoplasmacytic inflammation is present throughout the propria, surrounding hyperplastic oesophageal mucous glands.
In the proventriculus the surface mucosa has epithelial hyperplasia, diffuse lymphocytic inflammation and multifocal erosions. Numerous bundles of large thick bacilli (probably Macrorhabdus sp) are present on the mucosal surface, in proventricular crypts and where the mucosa is eroded. In some eroded areas these organisms have penetrated the epithelium. The submucosal proventricular glands are moderately hyperplastic and there are multifocal areas of lymphoplasmacytic inflammation associated with mild glandular epithelial necrosis.
Morphological diagnosis
1. Oesophagitis, proliferative, chronic, diffuse, severe, with intralesional nematodes (probably Capillariasp) and protozoa (possibly Trichomonas sp).
2. Proventriculitis, hyperplastic and lymphoplasmacytic, chronic, diffuse, moderate, with associated bacilli (probably Macrorhabdus ornithogaster).
Aetiology
The nematode (possibly Capillaria annulata or C. contorta) is the major pathogen in the oesophagus, although a contributing role for Trichomonas (possibly T. gallinae) cannot be ruled out. The cause of the proventriculitis is not clear. The presence of Macrorhabdus ornithogaster (also known as gastric yeast, previously Megabacterium sp) in some areas suggests these organisms might be opportunistic rather than primary pathogens. M. ornithogaster usually colonises the isthmus (the junction between proventriculus and ventriculus). The lympoplasmacytic response suggests other agents, including viruses, should also be considered.