Conference 04 - 2025 Case: 01 20250917

Wednesday Slide Conference, 2025-2026, Conference 4, Case 1

Signalment:

Unknown age, male, black-tailed prairie dog, Cynomys ludovicianus

History:

Prairie dog sourced from a zoologic collection. Clinical presentation for acute ptyalism, easily captured, poor vision. Clinical examination noted superficial healing wounds on bilateral forearms, facial scarring with intermittent swellings, incisor malocclusion, elongate buccal aspects of mandibular molars, bilateral tongue ulceration.

Gross Pathology:

External examination of the lungs was normal. On serial sectioning and trimming in representative sections of lung a single small sample of lung tissue was noted as floating low in formalin solution; on examination of one aspect of the cut section the lung was pale tan and consolidated with multifocal pale tan, circular, soft foci (exudate filling bronchi). The total volume of affected lung mass was less than 10%.

Laboratory Results:

Initial Gram, GMS, and Acid-Fast stains of affected lung tissue did not identify bacterial or fungal microorganisms. Please see comments below for details on follow-up ancillary diagnostics.

Microscopic Description:

Lung, multiple sections. Within a single section of lung, approximately 75% of the bronchial, bronchiolar, and alveolar lumina contain overall large numbers of neutrophils, macrophages, large multinucleated cells, cellular debris, homogenous eosinophilic material, fibrillary eosinophilic material, and occasionally scattered erythrocytes. The multinucleated cells are often large and bizarre in appearance, some containing approximately 40 nuclei. The cytoplasm of these multinucleated cells is eosinophilic and variably granular to homogenous. A subset of these multinucleated cells contains few distinct optically clear vacuoles, while others demonstrate phagocytosis of few neutrophils. There is mild vascular congestion throughout, and there are small clusters of lymphocytes cuffing airways multifocally.

Contributor's Morphologic Diagnoses:

Pneumonia, bronchoalveolar, suppurative, histiocytic, focal, subacute, severe with intraluminal multinucleated giant cells.

Contributor's Comment:

Initial Gram, GMS, and acid-fast stains of affected lung tissue did not identify bacterial or fungal microorganisms. Viral inclusions were not evident on H&E-stained sections of the affected lung and other tissues evaluated during necropsy evaluation.

Pathologists reviewing the case considered the possibility of multinucleated giant cells versus syncytia. Pulmonary syncytia in mammalian species may be seen with orthopox viruses, herpes viruses, and respiratory syncytial viruses.⁵ Among the orthopox viruses, monkeypox virus would be a possible differential that must be considered given this species’ vulnerability to the virus and the zoonotic potential.^2,7 Necrotizing bronchopneumonia has been reported in prairie dogs with monkeypox viral infection, and histologic descriptions have included syncytia and poorly discernible eosinophilic intracytoplasmic inclusions.^4,6

Formalin-fixed, paraffin-embedded lung tissue was submitted to the Center for Disease Control and Prevention (CDC) for further evaluation. Immunohistochemical staining for orthopoxviruses was not detected. Additional immunohistochemical stains for canine distemper virus, measles virus, and respiratory syncytial virus were reported negative. PCR testing for human parainfluenza virus (1-4) and respiratory syncytial virus were also reported negative.

Transmission electron microscopy provided ultrastructural evidence of bacteria within giant cells, with no viral particles identified.

The sample was immunoreactive on a polybacterial immunohistochemical assay, but negative for select gram-negative bacteria on a separate immunohistochemical assay. PCR testing for the groEL gene of mycobacteria and Nocardia spp. was positive, with subsequent sequencing identifying Nocardia spp. PCR testing for gram-negative bacteria specific 16S rRNA gene was positive for Pasteurellaceae. Immunohistochemical staining for Pasteurella multocida was negative. PCR testing for gram-positive bacteria specific 16S rRNA gene was indeterminate. Repeat acid fast staining (Fite’s stain) identified long filamentous rods within the giant cells.

Contributing Institution:

Arizona Veterinary Diagnostic Laboratory, https://azvdl.arizona.edu

JPC Diagnoses:

TBD

JPC Comment:

TBD

References:

Ackermann MR. Inflammation and Healing. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:104-170.
Essbauer S, Pfeffer M, Meyer H. Zoonotic poxviruses. Vet Micro. 2010;140:229-236.
Gharun K, Senges J, Seidl M, Lösslein A, Kolter J, Lohrmann F, Fliegauf M, Elgizouli M, Alber M, Vavra M, Schachtrup K, Illert AL, Gilleron M, Kirschning CJ, Triantafyllopoulou A, Henneke P. Mycobacteria exploit nitric oxide-induced transformation of macrophages into permissive giant cells. EMBO Rep. 2017;18(12):2144-2159.
Guarner J, Johnson BJ, Paddock CD, Shieh WJ, et al. Monkeypox transmission and pathogenesis in prairie dogs. Emerg Inf Dis. 2004;10(3):426-431.
Hughes L, Olson VA, Damon IK. Poxviruses. In: Jorgensen JH, ed. Manual of Clinical Micrology. 11th ed. ASM Press; 2015.
Langohr IM, Stevenson GW, Thacker HL, Regnery RL. Extensive lesions of monkeypox in a prairie dog (Cynomys sp.). Vet Pathol. 2004;41(6):702-707.
Yarto-Jaramillo E. Rodentia. In: Miller RE ed. Fowler’s Zoo and Wild Animal Medicine. Vol 8. Saunders; 2015.