Case A (Fowl Cholera)
Low incidence of periorbital and wattle swelling in a layer flock
Example histopathological description
This section of wattle is expanded by a large, densely eosinophilic amorphous mass deep in the dermis. It has an irregular outline, is associated with considerable clefting and loculation, and is separated from the adjacent dermis by a continuous layer of epithelioid macrophages, many of them multinucleated. The mass for the most part consists of cell debris consistent with effete leucocytes; however, there are occasional inspissated but recognisable remnants of blood vessels and nerves. There are a few sharply-demarcated, finely granular, basophilic bodies consistent with bacterial colonies within the outer layers of the coagulum at several locations. Thrombosis, medial degeneration and heavy heterophil infiltration is evident in occasional vessels adjacent to the central mass. The dermis surrounding the mass has variably extensive high-protein oedema alternating with pronounced hyperplasia. Blood vessels are prominent and reactive and are surrounded by variable numbers of lymphocytes and other leucocytes. Free-floating macrophages with granular cytoplasm are prominent in oedematous tissue.
Dermatitis, necrotizing, chronic, extensive, severe, with caseous necrosis of wattle skin (dermal sequestrum)
Localised dermal Pasteurella multocida infection (fowl cholera)
Avian coryza (Haemophilus spp. infection), other non-specified bacterial infections and complications of avian influenza (lower-virulence strains) should be considered.
Case B (Salmonellosis and Mulga liver)
A ‘mickey’ bull (an unmarked animal sometimes called a ‘scrub bull’) from western Queensland was yarded and developed scouring and weight loss. A black liver was noted at necropsy.
Example histopathological description
This is a section of liver which includes the capsular surface. There is a prominent acinar pattern due to moderately heavy pigmentation of periportal hepatocytes whose cytoplasm contains fine black granules. The frequency of pigmented hepatocytes diminishes with distance from the triads. Periportal Kupffer cells contain heavier deposits of this pigment. Sinusoids throughout contain more cells than normal, these are predominantly plump mononuclear cells and include macrophages replete with golden pigment that is different from that in periportal zones. There are scattered foci of necrosis, variable in size and extent, which are essentially randomly distributed, although some show a predilection for periacinar/midzonal locations. In addition to locally extensive hepatocyte degeneration and coagulative necrosis, these foci contain unevenly distributed infiltrates of large mononuclear cells, possibly activated histiocytes. Hepatocyte nuclei throughout are slightly enlarged and have a vesicular appearance with mild prominence of nucleoli. Portal stroma is often excessively dense and there is some mild bile ductular proliferation.
1. Hepatitis, non-suppurative, necrotizing, acute/subacute, multifocal, moderate, with sinusoidal leucocytosis.
2. Pigmentation (melanin/lipofuscin), periportal (hepatocytes and Kupffer cells), chronic, diffuse, moderate.
3. Hepatocellular ‘activation’, chronic, diffuse, mild
4. Fibrosis, portal, chronic, focal, mild, with mild focal bile duct proliferation.
Differential aetiological diagnoses
1. Septicaemic salmonellosis, or non-specified bacteraemia
2. Environmental melanosis/lipofuscinosis
3. Mild hepatopathy, possibly low-grade hepatoxicity
4. Mild multifocal senile change
This is probably a case of severe Salmonella infection, which might have been confirmed had fresh chilled liver or mesenteric lymph node been submitted for culture. The other changes are mostly either incidental or age-related, but it is possible that there has been exposure to plant or environmental chemicals sufficient to produce mild hepatopathy.