Sporadic sudden deaths occurred in dry heifers at pasture. An enlarged spleen was present at necropsy.
Example Histopathological Description
This section contains several fragments of well preserved and well stained splenic tissue without a splenic capsule. The red pulp is diffusely and markedly congested, with the vascular spaces distended by large numbers of intact (sludged) erythrocytes and the sparse splenic cords containing small numbers of macrophages and lymphocytes. The oedematous trabeculae and the white pulp are widely separated by the expanded red pulp. The white pulp is attenuated due to lymphocyte depletion (lymphocytolysis) within periarteriolar lymphoid sheaths and the absence of intact splenic follicles. There is minimal erythrophagocytosis but throughout the red and white pulp are moderate numbers of haemosiderophages, the latter an incidental finding. Throughout the section are small to massive clusters of intravascular, extracellular bacilli measuring 1×8 μm, and often arranged in chains.
Splenic congestion; acute, diffuse, severe, with lymphoid depletion and abundant intravascular bacilli.
This is a case of anthrax. Bacillus anthracis should be the first diagnostic rule-out. When anthrax is suspected (e.g. sudden death in an anthrax endemic area or where anthrax has occurred at any time), examination of blood smears should precede necropsy. The massive numbers of the vegetative form of B anthracis in the internal organs of a carcass are destroyed by putrefaction within 48 hours. However, if the organism is exposed to air (e.g. during necropsy) sporulation occurs and the spores are highly resistant – they survive in soil for at least 15 years. A blood smear taken before necropsy will show typical B anthracis morphology in smears, i.e. Gram-positive vegetative bacilli with square ends when apposed, and a pink capsule when stained by methylene blue or Giemsa.
In non-anthrax endemic areas the differential diagnosis will include Clostridial septicaemia (Clostridium spp. morphology in smears: Gram-positive bacilli with rounded ends and no capsule) and other septicaemic bacterial agents that cause splenomegaly (e.g. Salmonella spp.). Acute death from toxic plants such as those containing fluoracetate may also be considered along with agents that cause acute haemolytic anaemia, such as haemoparasites (Babesia spp, Anaplasma spp, Theileria spp).
Recently imported (to Australia) adult female scarlet macaw, with a history of weight loss. The cloaca contained multiple papillomatous masses. At necropsy a 4 mm diameter mass was found in the liver.
Example Histopathological Description
Cloaca (1): Anterior proctodeum/coprodeum. Skin and caecal mucosa is separated by a wide zone of fibrovascular stroma containing smooth and striated muscle. The caecal mucosa is uniform in depth with relatively straight tubular glands lined by intact tall columnar epithelium. The lamina propria between the glands is mildly expanded by a dense population of plasma cells, lymphocytes and smaller numbers of macrophages and heterophils. The surface epithelium is desquamated (which is artefactual, rather than erosive).
Cloaca (2): Posterior proctodeum/vent. In this sample, the mucosal epithelium is expanded by exophytic irregular papillary projections of markedly hyperplastic stratified squamous epithelium on a fibrovascular stromal core. The neoplastic squamous epithelial cells exhibit normal maturation, progressing from a prominent hyperplastic stratum basale with increased numbers of mitotic figures (up to 3/hpf) and occasional suprabasilar mitoses through to a thickened stratum spinosum. The stratum corneum is also thickened by parakeratotic hyperkeratosis. There is frequent individual keratinocyte apoptosis and, superficially, aggregates of keratinocytes are sloughed, forming multifocal surface crusts admixed with scattered erythrocytes, cellular debris, and scattered colonies of bacterial cocci. The fibrous connective tissue core, and to a greater extent the subjacent connective tissue, is infiltrated by multifocal to coalescing aggregates of lymphocytes, plasma cells, and fewer heterophils.
Liver: Replacing approximately 40% of the hepatic parenchyma is a poorly demarcated, infiltrative, densely cellular neoplastic mass. The cells of the neoplasm form anastomosing tubules and acini separated by a fine fibrovascular stroma. The tumour cells are cuboidal with a small to moderate amount of faintly eosinophilic cytoplasm, variably-distinct cell margins and an oval nucleus with finely stippled chromatin and 1-2 small nucleoli. Occasional acini contain amorphous eosinophilic material. There is mild anisocytosis and anisokaryosis and an occasional mitotic figure (<1/hpf). Within the tumour are small, multifocal aggregates of lymphocytes with some plasma cells and rare heterophils. The adjacent hepatic parenchyma appears normal.
Cloaca (1): Cloacitis; lymphoplasmacytic, chronic, locally-extensive, mild.
Cloaca (2): Papilloma/papillomatosis.
Liver: Cholangiocellular (bile duct) carcinoma.
The differential diagnosis of cloacal papillomas + cholangiocellular (bile duct) carcinoma is as follows.
Psittacid herpesvirus (PsHV)
- PsHV-1 comprises 4 genotypes, all of which cause Pacheco’s disease.
- PsHV-1, genotypes 1, 2 and 3 have been associated with mucosal papillomas.
- PsHV-1 genotype 3 has been associated with mucosal papillomas and concurrent cholangiocellular (bile duct) carcinoma.
- PsHV-2 has been associated with cutaneous and mucosal papillomas in African grey parrots only. It was reported in an asymptomatic blue and gold macaw in the USA in 2006.
The differential diagnosis of cloacal papilloma/papillomatous lesions includes:
- Vitamin A deficiency
- Chronic irritation of the cloacal epithelium.