Case of the Month – July 2025

Signalment and History

An adult female WT deer was seen over multiple days with its fawn by a property owner. In the evening of July 19, 2025, the doe was noted to be moving very slowly and behaving somewhat abnormally. The property owner found the animal dead at 7:30AM the following day. After arranging the pickup of the deer by the local conservation officer of the Department of Natural Resources, the animal was submitted to the Minnesota Veterinary Diagnostic Laboratory for a postmortem examination.

Gross Findings

The carcass was in good postmortem condition and in adequate nutritional status. Mild subcutaneous edema was present over the head. The thoracic cavity contained a large volume of watery, yellow, translucent fluid. The lungs were diffusely voluminous, heavy, and wet. The interlobular septa were expanded by clear fluid.

Figure 1.  Tissue from the white-tailed deer. Hydrothorax and severe acute alveolar and interstitial pulmonary edema. There is clear, yellow, watery fluid in the thoracic cavity. The lungs are voluminous, wet and heavy. The interlobular septa of the lungs are severely expanded by clear fluid.

Histopathological findings

No significant histological findings aside from the expansion of the interlobular septa was present in the examined organs (lung, brain, eye, liver, abomasum, intestine, kidney, heart, skeletal muscle, adrenal glands, and femoral diaphyseal bone marrow).

Ancillary Testing

• Bacteriology (aerobic culture): Lung, liver, and small intestine – no significant growth
• Bacteriology (anaerobic culture): Large intestine – Clostridium perfringens (3+)
• Parasitology (fecal floatation): 1 to 10 strongyle type eggs per field
• Retropharyngeal lymph node: CWD prion protein: negative (Wisconsin Veterinary Diagnostic Laboratory)
• Virology - 
  • Spleen sample: positive for Epizootic Hemorrhagic Disease (EHD) virus by PCR (tested at NVSL; Ct – 20.4); sequencing: EHD-2 serotype negative for Bluetongue virus by PCR (tested at NVSL)
  • Brain samples: negative for rabies virus antigen by DFA (tested at Minnesota Department of Health); negative for WNV and EEEV by PCR (tested at Minnesota Department of Health)
  • Liver sample: negative for deer adenovirus-1 (tested at UC Davis, CA)

Morphologic Diagnosis

1. Lungs, alveolar and interstitial edema, marked, acute
2. Hydrothorax, marked
3. Skin (head), subcutaneous edema, acute, mild

Disease

Epizootic Hemorrhagic Disease.

Etiology

Epizootic Hemorrhagic Disease Virus 

Comments

Epizootic hemorrhagic disease (EHD) is a reportable, vector-borne disease of wild and domestic ruminants caused by an Orbivirus closely related to the bluetongue virus (BTV). Seven EHD virus (EHDV) serotypes are currently recognized and have been reported across five continents.

EHD primarily affects white-tailed deer (Odocoileus virginianus) but can also infect other wild ruminants, including mule deer (O. hemionus), pronghorn antelope (Antilocapra americana), elk (Cervus canadensis), and Barbary deer (C. elaphus barbarus). The virus infects endothelial cells causing widespread endothelial cell injury, leading to vascular leakage, edema, and hemorrhage. The clinical course may be peracute (sudden death), acute, or chronic. The injury may be histologically not apparent in peracute cases. In chronic cases, ulcerations of the upper gastro-intestinal tract, forestomachs and abomasum as well as hoof lesions occur. 

In recent years, EHDV has been detected farther north in the United States and Canada, regions where it was historically absent. This geographic expansion is thought to be associated with climate change (e.g. allowing the Culicoides spp. midges werving as vectors to expand northwards) and viral genetic adaptation.

The first detection of EHDV in Minnesota occurred in 2019, when the EHD-2 serotype was associated with mortality in free-ranging white-tailed deer. The following year, the EHD-6 serotype was identified during an outbreak among captive reindeer.

The primary differential diagnoses include bluetongue virus infection, deer adenovirus-1 infection, and bacterial septicemia. Laboratory testing, such as PCR, virus isolation, or serology, is required to confirm the diagnosis.

References

1. Jiménez-Cabello L, Utrilla-Trigo S, Lorenzo G, Ortego J, Calvo-Pinilla E. Epizootic Hemorrhagic Disease Virus: Current Knowledge and Emerging Perspectives. Microorganisms. 2023 May 19;11(5):1339. doi: 10.3390/microorganisms11051339. PMID: 37317313; PMCID: PMC10224379.
2. Ruiz-Fons F, García-Bocanegra I, Valero M, Cuadrado-Matías R, Relimpio D, Martínez R, Baz-Flores S, Gonzálvez M, Cano-Terriza D, Ortiz JA, Gortázar C, Risalde MA. Emergence of epizootic hemorrhagic disease in red deer (Cervus elaphus), Spain, 2022. Vet Microbiol. 2024 May;292:110069. doi: 10.1016/j.vetmic.2024.110069. Epub 2024 Mar 31. PMID: 38569324.
3. Torii E, Wünschmann A, Torchetti MK, Koster L, van Geelen A, Atchison R, Rivas A. Outbreak of epizootic hemorrhagic disease in captive reindeer (Rangifer tarandus). Vet Pathol. 2024 Mar; 61(2):298-302. doi: 10.1177/03009858231196797. 

Funding provided by the Minnesota Environment and Natural Resources Trust Fund.