In crossbred weaner sheep six months of age, eight in a group of 2000 were found dead. They were grazing dry annual grasses and weeds.
Example Histopathological Description
The section is of three segments of rumen, the largest of which has a fragment of plant material in the middle of an area of caseous necrosis occupying the full thickness of the muscular layer. This is surrounded in turn by a dense infiltrate of leucocytes; predominantly neutrophils but with some large mononuclear cells. Areas of basophilic granularity in the necrotic zone, and within the plant fragment, probably represent bacteria. Haemorrhage, oedema and neutrophil infiltrates extend from the necrotic focus to the subjacent serosal surface, which bears amorphous basophilic deposits.
In the same section as the foreign body there is a poorly-demarcated area of haemorrhage, neutrophil infiltration, oedema and vasculitis with thrombus formation in the lamina propria, including that of an overlying villus. The mucosa of all sections shows extensive but discontinuous vacuolar change of superficial keratinocytes. There is extensive focal subcorneal formation of vesicles containing neutrophils.
Abscess; intramural, subacute, with foreign-body (plant) and associated focal peritonitis (serositis).
Rumenitis; focal, superficial, pustular and vesicular with extensive moderate mucosal spongiosis.
The diffuse superficial mucosal degeneration and vesicular inflammation is more likely to be due to a soluble irritant component of rumen content than to simple mechanical abrasion by rough feed. Similar vacuolar degeneration has been recorded in poisoning by Kikuyu grass, prickly paddy melon (Cucumis myriocarpus), oxalate and urea (ammonia), and it occurs in rumenal acidosis.
The deeper focal mural inflammation; however, is clearly related to penetration of the rumen wall (presumably from the mucosal surface) by a plant fragment that has set up a severe localized bacterial infection that is extensive enough to involve the subjacent serosa. It is unlikely that this penetration has been facilitated by the more diffuse mucosal damage, since the abscess, although not yet encapsulated, appears to be of longer standing than the mucosal changes.
Tissue from a two year old goat. Two goats in a small group developed diarrhoea and severe weight loss over about a week and were then found dead.
Example Histopathological Description
The section is of curved elastic cartilage with a short segment of sparsely-haired squamous epithelium on one side and areolar tissue and a small amount of striated muscle on the other; consistent with external ear. The epidermis shows mild diffuse superficial spongiosis and mild hyperplasia. There is moderately extensive perivascular infiltration by mononuclear cells (predominantly lymphocytes), associated with which are occasional small deposits of brown pigment. Apocrine glands are prominent, many are dilated, one or two are impacted by inspissated secretion, and there are occasional small pigment deposits associated with these also.
In the ear canal there is a dense mass of necrotic inflammatory cells, nucleated and non-nucleated squames, coccoid bacteria and amorphous eosinophilic material. This inspissated mass forms a matrix for metazoan forms with finely-ridged cuticle and other features suggestive of mites. The mass also contains eggs and cuticular debris.
External otitis; chronic, mild, lymphoplasmacytic, with mites.
Otocariasis; probably due to Psoroptes cuniculi (more likely than Raillietia sp.)
This condition is unlikely to have significantly contributed to the animal’s weight loss or diarrhoea. The severity of the infection may have been influenced by inanition brought on by a more serious systemic condition.