Gross Findings: An adult male Northern Shoveler in poor body condition and fair postmortem state is presented for necropsy. On external examination, multiple small ulcerations are present on the soles of both feet. The keel is prominent. The mid cervical vertebral column is fractured (euthanasia). On internal examination, there is a minimal amount of subcutaneous, visceral, and epicardial fat. Pectoral muscle is moderately atrophied. There is a focally extensive area of hemorrhage surrounding the neck fracture. Abdominal air sacs are thickened and tan.

Histopathological Findings: Diffusely, the air sac epithelium is replaced by or covered with a thick layer of fibrin admixed with heterophils and fewer macrophages and eosinophilic and cellular necrotic debris (Fig. 1A). Gram negative bacterial rods are present in the air sac wall or within the cytoplasm of macrophages (Fig. 1A inset). Diffusely, the connective tissue wall is expanded by edema and moderate numbers of heterophils (Fig. 1B). The epicardium is expanded by a thick layer of fibrin admixed with moderate to large numbers of heterophils and macrophages and eosinophilic and cellular necrotic debris (Fig. 1C, D). Fibrin deposits are occasionally present in hepatic sinusoids (Fig. 1E). Hepatocytes and Kupffer cells often contain intracytoplasmic brown pigment (hemosiderin). There is severe splenic lymphoid depletion and accumulations of fibrin are present in the white pulp (Fig. 1F).

Diagnostic Test Results: Routine bacterial culture of the air sac and liver yielded pure cultures of Riemerella anatipestifer. Fungal culture of the air sac yielded no fungal growth. Circovirus was detected in the liver by PCR. A WNV RT-PCR screen using kidney and spleen was negative. An avian influenza virus matrix RT-PCR screen using tracheal and cloacal swabs was negative.

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Morphologic Diagnoses:

1. Airsacculitis, fibrinous and heterophilic, diffuse, severe with intralesional gram negative bacteria
2. Epicarditis, fibrinous, heterophilic and granulomatous, multifocal, severe
3. Hepatic and splenic fibrin deposition
4. Splenic lymphoid depletion, diffuse, severe

Etiology: Riemerella anatipestifer (formerly Pasteurella anatipestifer) is a non-spore forming, non-motile, catalase and oxidase positive, gram negative rod. There are more than 20 immunotypes (or serotypes). Riemerella anatipestifer can be a part of the normal flora in the upper respiratory tract of some domestic and wild duck species. This adult duck also tested positive for circovirus which may have compromised the immune system and made it more susceptible to infection. Cause of death in two of the three ducks necropsied from this event was R. anatipestifer. Mycobacteriosis was the cause of death in the third duck. The cause of the overall mortality event is not known.

Disease: New duck disease.

Distribution: Worldwide.

Host range: Ducks, geese, turkeys, pheasants, and chickens; young are more susceptible than adults.

Transmission: In ducks, transmission is via the respiratory route or can occur when introduced into lesions in foot webbing.

Clinical signs: Ducklings have ocular and nasal discharge, mild coughing and sneezing, tremors of the head and neck, depression, and incoordination progressing to obtundation and death. Terminally, ducklings may lie on their backs and paddle their legs.

Pathology: Lesions include fibrinous pericarditis, perihepatitis, airsacculitis, meningitis, and mucopurulent or caseous salpingitis. Hepatosplenomegaly and pneumonia may occur. Mortality in ducks usually ranges from 2% to 50%.

Diagnosis: Susceptible species with characteristic histopathology; bacterial culture; PCR and subsequent sequencing. Because R. anatipestifer can be part of normal flora, culture alone is not sufficient for a diagnosis of new duck disease.

Public health concerns: No known human health concerns.

Management: Management practices in domestic poultry include strict biosecurity, vaccination, and all-in/all-out management systems.

References:

• Chikuba T, Uehara H, Fumikura S, Takahashi K, Suzuki Y, Hoshinoo K, Yamamoto Y. 2016. Riemerella anatipestifer infection in domestic ducks in Japan, 2014. J Vet Med Sci: 78:1635–1638, https://doi.org/10.1292/jvms.16-0278
• Merck Veterinary Manual. 2016. Riemerella anatipestifer infection in poultry, https://www.merckvetmanual.com/ Accessed January 10, 2022.
• Ryll M, Christensen H, Bisgaard M, Christensen JP, Hinz KH, Köhler B. 2001. Studies on the prevalence of Riemerella anatipestifer in the upper respiratory tract of clinically healthy ducklings and characterization of untypable strains. J Vet Med B Infect Dis Vet Public Health: 48:537–546, https://doi.org/10.1111/j.1439-0450.2001.00471.x