Signalment:  
Gross Description:  
Histopathologic Description:
Morphologic Diagnosis:  
Lab Results:  
Condition:  
Contributor Comment:  
Characteristic pathological findings, such as pericarditis and perihepatitis observed in the present case, are highly suggestive of RA infection. However, a definitive diagnosis of RA infection requires isolation and identification of RA from ducks suspected to be infected.9,10,14 There are difficulties associated with the identification of RA.9,10 Riemerella anatipestifer is characterized by the absence of species-specific biochemical properties.5 Genetic sequencing of bacterial 16S ribosomal RNA and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry are currently considered useful for the identification of RA.4,8,13,16
Other bacterial infections such as colibacillosis may cause gross lesions similar to those seen in RA-infected ducks.6 The differential diagnosis also include salmonellosis, pasteurellosis, streptococcosis, and Coenonia anatina infection.14
JPC Diagnosis:  
Conference Comment:  
As mentioned by the contributor, fibrinous pericarditis and epicarditis are the most characteristic lesions of RA. This case represents the chronic form of the disease, with progression from fibrinous to granulomatous epicarditis with abundant granulation tissue on the epicardial surface. The pericardium was likely removed prior to tissue processing and is not present in the microscopic sections submitted for evaluation.
Many conference participants had little experience with this entity histologically, which led to a discussion of the differential diagnosis for epicarditis and polyserositis in avian species. While not a typical presentation for Pasteurella multocida, fowl cholera can cause similar lesions in poultry, chickens, and waterfowl. 4 Salmonella pullorum causes peritonitis and death in hatchling chicks; and peritonitis, arthritis, and pericarditis in adults, and is often characterized by large hetrophilic granulomas in the myocardium. Escherichia coli and other coliform infections also can lead to fibrinous and heterophilic rmyocarditis, and should be considered as a differential in most avian species.4 Coenonia anatine, described by the contributor and briefly discussed during conference, also causes exudative serositis in ducks and geese.12Riemerella columbina causes similar disease as RA in pigeons.12 While not mentioned during conference, West Nile Virus, an arbovirus of the family Flaviviridae, should also be considered as a differential for necrotizing myocarditis of many avian species, with young chickens and geese being most likely to develop clinical disease and mortality. 1
Participants also discussed the three main rule-outs for polyserositis, pneumonia, and polyarthritis in pigs; among these include Haemophilus parasuis, Mycoplasma hyorhinis, and Streptococcus suis. 5 In horses, the most likely etiologies for polyserositis are Streptococcus equi and Streptococcus zooepidemicus. 2
References:
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