JPC SYSTEMIC PATHOLOGY

CARDIOVASCULAR SYSTEM

 March 2025

C-V03

 

Signalment (JPC # 2307591): White-tailed deer (Odocoileus virginianus)

 

HISTORY: This deer had myocardial hemorrhage and hemorrhage in the pulmonary artery.

 

HISTOPATHOLOGIC DESCRIPTION: Heart: Transmurally and multifocally affecting 60 percent of this section, surrounding and often obscuring blood vessels, expanding the perimysium and endomysium, and separating, surrounding and replacing cardiac myofibers there is abundant hemorrhage, fibrin, edema, moderate numbers of macrophages which often contain intracytoplasmic erythrocytes (erythrophagocytosis) and fewer viable and degenerate neutrophils. Multifocally within small vessels the endothelium is often hypertrophic/reactive, and the tunica intima is multifocally discontinuous and the vessel wall contains cellular and karyorrhectic debris, hemorrhage, fibrin, scant edema, and is infiltrated by few neutrophils (necrotizing vasculitis). Cardiac myocytes are occasionally lost and replaced by hemorrhage or moderate numbers of macrophages and neutrophils. Multifocally myocytes are hypereosinophilic, shrunken and fragmented, with loss of cross striations, and the presence of contraction bands and pyknotic or karyorrhectic nuclei (necrosis). Occasional myocytes contain basophilic granular material within the sarcoplasm (mineral). Lining the epicardial surface there is multifocal mesothelial cell hypertrophy.

 

MORPHOLOGIC DIAGNOSIS: Heart: Pancarditis, necrohemorrhagic, multifocal, moderate, with necrotizing vasculitis, white-tailed deer (Odocoileus virginianus), cervid.

 

ETIOLOGIC DIAGNOSIS: Orbiviral myocarditis

 

CAUSE: Cervid orbivirus 1 and 2, epizootic hemorrhagic disease virus (EHDV)

 

CONDITION: Epizootic hemorrhagic disease (EHD) of deer

 

GENERAL DISCUSSION: 

• Epizootic hemorrhagic disease virus (EHDV): Arthropod-borne virus (spread by Culicoides spp.), family Reoviridae, genus Orbivirus; non-enveloped, linear dsRNA 
• 7 serotypes recognized, best illustrated are: EHDV-1 and EHDV-2 present in Africa, Australia, North America; Ibaraki virus (IBAV) is a strain of EHDV-2, isolated in Japan
• EHDV-1 and EHDV-2 are endemic in the United States
  • Most significant viral disease of white-tailed deer (highly susceptible; causes fatal hemorrhagic disease); less severe disease in mule deer, black-tailed deer, elk, pronghorn antelope, cattle, sheep, bighorn sheep, and yaks
  • Black-tailed deer and pronghorn antelope have a higher survival rate; elk are only very mildly affected
  • Sheep have been experimentally infected, but only develop mild disease with gross lesions resembling bluetongue. 
• EHD and bluetongue (BTV, M-V01) are both orbiviruses
  • Gross lesions, clinical signs and pathogenesis are very similar, indistinguishable
  • Contrast to BTV, EHDV has very low pathogenicity in sheep

 

PATHOGENESIS:

• Midge (Culicoides spp.) bite > primary viral replication in macrophages within local draining lymph nodes > viremia 4-10 days post infection, with infection of erythrocytes > infects secondary replication sites (especially the spleen and lung) and replicates within endothelial cells throughout the body > endothelial damage > microvascular thrombosis and increased vascular permeability > hemorrhage, edema, thrombosis and ischemic necrosis in many tissues 
  • Midges can transmit the virus 10-15 days after the initial ingestion of infected blood, once the virus infects its salivary glands 
• Have a long viremia due to viral particles “hidden” in the pits of erythrocyte surfaces; cattle may act as a reservoir as the virus remains associated with their erythrocytes for the life-span of the infected cell 

 

TYPICAL CLINICAL FINDINGS:

• General: Fever, depression, lymphopenia 
• Vascular: Endothelial damage from viral infection initiates local microvascular thrombosis and permeability > disseminated intravascular coagulation
• Edema of head, neck, conjunctiva, and long fascial planes 
• Respiratory distress (pulmonary edema)

 

TYPICAL GROSS FINDINGS: 

• Widespread multisystemic hemorrhage and edema, especially in gastrointestinal tract and at the base of the pulmonary artery in the tunica media (near-pathognomonic)
• Extensive ulceration of the dental pad, tongue, palate, rumen, reticulum, omasum
• Necrosis and sloughing of antler velvet and hooves in survivors

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Arterioles and venules markedly affected, resulting in fibrinoid vasculitis 
• Swollen endothelium; fibrin and platelet thrombi in small vessels, with edema and hemorrhage in surrounding tissue
• Ischemic necrosis of many tissues

 

ADDITIONAL DIAGNOSTIC TESTS: 

• Virus isolation 
• EHDV RT-PCR
• EHDV cross reacts with Bluetongue (BTV) in some serologic tests (ELISA)

 

DIFFERENTIAL DIAGNOSIS:

• Bluetongue (BTV) Orbivirus (M-V01): Clinical indistinguishable; BTV and EHDV can be simultaneously involved in outbreaks and have been simultaneously isolated from Culicoides 
• Adenovirus: Black-tailed and white-tailed deer, other cervids: Pulmonary edema, systemic vasculitis leading to disseminated intravascular coagulopathy, intranuclear inclusions in endothelial cells

 

COMPARATIVE PATHOLOGY:

Other orbiviruses of veterinary importance:

• Bluetongue (BTV, M-V01): Domestic and wild ruminants (especially sheep)
• Ibaraki disease (IBAV): Cattle in Japan infected with EHDV-2; causes severe ulceration from the mouth to the abomasum, esophageal myonecrosis, difficulty swallowing, secondary aspiration pneumonia, abortion and stillbirths
• African horse sickness (P-V23): Another oribivirus transmitted by midges; acute pulmonary edema and death; periorbital and nuchal ligament edema, hydropericardium

 

References:

1. Howerth EW, Nemeth NM, Ryser-Degiorgis MP. Cervidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:157, 159-161. 
2. Jones MEB, Gasper DJ, Mitchell E. Bovidae, Antilocapridae, Giraffidae, Tragulidae, Hippopotamidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:128. 
3. Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier; 2016:431.
4. Uzal FA, Plattner BL, Hostetter JM. Alimentary System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016:39,136-9. 
5. Vinueza RL, Cruz M, Breard E, Viarouge C, Zanella G. Bluetongue virus and epizootic hemorrhagic disease virus survey in cattle of the Galapagos Islands. J Vet Diagn Invest. 2019;31(2):271-275.

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