March 2009

Case A

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A male Sacred or Hamadryas baboon (Papio hamadryas) with a history of chronic weight loss, sudden collapse and death.

Example Histopathological description

This is a transverse section of brain at the level of the basal ganglia. It contains grey matter, white matter and ependyma but does not include the cerebral cortex or meninges.  Multiple and extensive foci of malacia and haemorrhage, associated with prominent perivascular cuffing, vasculitis and thrombosis, are present in the grey and white matter. The inflammatory infiltrate is predominately neutrophilic and involves the walls of vessels and the surrounding neuropil – it extends to, but does not involve, the ependyma.  Some vessels have segmental fibrinoid change. In places, the neuropil has mass accumulations of intact and degenerating neutrophils. Haemorrhage is prominent in the areas of necrosis. Some blood vessels have large numbers of coccoid bacteria, often encircling the wall. The bacteria, which are also in the neuropil in small numbers, are Gram-positive cocci arranged in clumps, chains and pairs. Incidental findings include ceroid-like pigment in some glial cells and neurones, and occasional laminated mineral concretions (possible psammoma bodies).

Morphological diagnosis

Encephalitis; suppurative, acute, multifocal, severe, with vasculitis and intralesional Gram-positive cocci.

Aetiological diagnosis

Bacterial encephalitis, probably Streptococcal.

Significance of findings

There are features of the histopathology that suggest the probability of this brain lesion having a septicaemic or embolic pathogenesis. There is possibly a lesion elsewhere in the animal.  Streptococcal infections are often seen in association with immune suppression.  The incidental findings suggest this may have been an aged animal, perhaps another contributing factor. Note that the Streptococcal species known to infect primates have zoonotic potential.

This is the same animal with colonic Trichuriasis circulated in December 2008 (Case A).The colonic lesion was considered an incidental finding. The Streptococcus was considered most likely to be Streptococcus pneumoniae.

Case B

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A minimal disease piggery with losses occurring in a sow unit, associated with coughing, cyanosis, respiratory distress and death, 2-3 months after introduction of gilts from a local sale.

Example histopathological description

This section of lung includes several lobules and contains pleura on one surface. The bronchi and bronchioles have severe, diffuse epithelial hyperplasia with a minimal lumenal exudate of neutrophils, macrophages, oedema fluid and epithelial debris. These airways are surrounded by marked lymphoid hyperplasia, admixed with histiocytes and plasma cells.  Peribronchial and peribronchiolar smooth muscle is mildly hypertrophic. Most alveoli contain protein-rich oedema fluid, many alveolar macrophages, occasional multinucleated cells (syncytia or giant cells) and fewer neutrophils. There is multifocal, mild, type II pneumocyte hyperplasia and the alveolar interstitium has variable, mild to moderate infiltrates of macrophages, lymphocytes and plasma cells. Some alveolar walls also have lymphoid clusters surrounding small blood vessels. Interlobular septa and subpleural spaces are mildly oedematous, but relatively spared.

Morphological diagnosis

Bronchointerstitial pneumonia; lymphohistiocytic, subacute to chronic, diffuse, severe

Aetiological diagnosis

Mycoplasmal pneumonia caused by Mycoplasma hyopneumoniae

Differential diagnosis and comments

The differential diagnosis includes pneumonia caused by porcine circovirus type 2, porcine reproductive and respiratory syndrome (PRRS) virus and porcine influenza virus infections. To confirm the diagnosis would require culture for M hyopneumoniae, or PCR, if fresh lung tissue is available. Submission of specimens to AAHL is recommended to rule out exotics (porcine reproductive and respiratory syndrome (PRRS) and swine influenza) and PCV2 infection.  There is a possibility that enzootic pneumonia has been introduced to this minimal disease piggery with the recently purchased gilts; hence, establishing the herd status through serological testing of cohorts for M hyopneumoniae is recommended.

This case was confirmed by culture of Mycoplasma hyopneumoniae. PRRS and other viral differentials were ruled out by testing at AAHL.