Epizootic hemorrhagic disease (EHD) in White-Tailed deer
By Andrés de la Concha-Bermejillo, DVM, MS, PhD, Pamela Ferro, MS, PhD, and Megan Schroeder, DVM Brooke Kehlenbrink*
*Fourth year veterinary student Food Animal Track TVMDL rotation.
The carcass of a male, intact, 92 lbs., 2.5-year-old white-tailed deer (WTD; Odocoileus virginianus) was presented for necropsy at the Texas A&M Veterinary Medical Diagnostic Laboratory’s (TVMDL) College Station laboratory. Three other deer in the same pen had died recently. Clinical signs included heavy breathing, stumbling, grinding of the teeth, coughing, lethargy, and death.
At necropsy, the WTD showed numerous skin abrasions with loss of hair, particularly over the ribs and bony prominences. There were areas of severe hemorrhage under the velvet of both antlers. Hemorrhages were also observed in skeletal muscles. Upon opening the thoracic cavity, numerous fibrous adhesions were found between the right cranial lung lobe, the parietal pleura and the pericardium. A large amount of foam was found in the lumen of the trachea. The lungs exhibited severe congestion and edema. Numerous petechiae were observed in the epicardium along the coronary groove. An irregularly-shaped area of severe mucosa ulceration of approximately two centimeters in diameter with ragged borders was found on the dorsal surface of the tongue (Figure 1). On the cut section through the lingual ulceration, an area of severe hemorrhage extended from the ulcerated surface to the skeletal muscle of the tongue. The remainder of the digestive tract and other abdominal organs exhibited various degrees of autolysis.
Histologically, mild infiltration of lymphocytes was found centered on the wall of a small blood vessel in the brain. There was ulceration of the mucosa of the tongue. In the submucosa under the ulcers, there was mild capillary proliferation and mild infiltration of lymphocytes. There was extensive hemorrhage in the skeletal muscle of the tongue. A section of skeletal muscle from the hind leg exhibited moderate to severe hemorrhage and moderate infiltration of neutrophils in the interstitium. The wall of some veins in the areas of hemorrhage exhibited necrosis.
Epizootic hemorrhagic disease (EHD) viral RNA was detected by qPCR (Ct value 26.40) in the spleen of the deer. Bluetongue virus (BTV) RNA was not detected. Based on the clinical history, gross and microscopic lesions and the detection of EHD viral RNA in the spleen, a diagnosis of EHD was established.
EHD is caused by epizootic hemorrhagic disease virus (EHDV), an arboviruses classified in the genus Orbivirus within the subfamily Sedoreovirinae of the family Reoviridae. EHDV is closely related to BTV, African horse sickness virus (AHSV) and equine encephalosis virus (EEV).
EHD is a double-stranded RNA virus with a 10-segmented genome.Presently there are 7 serotypes as determined by sequencing of the VP2 region of the genome. In the United States, EHDV serotypes 1, 2, and 6 have been identified. EHDis transmitted by hematophagous midges of the genus Culicoides. In North America, Culicoides sonorensis is the primary vector of EHDV.
EHD is an important cause of morbidity and mortality in WTD. EHDV infections have also been reported in other cervids (e.g. elk and mule deer) and bovids (e.g. cattle, bison and yaks), as well as pronghorn antelope. In the United States, infection of cattle with EHDV is generally asymptomatic, but fever, inappetence, decreased milk production, nasal and ocular discharge, conjunctivitis, ptyalism, oral and nasal ulcerations, and lameness have been reported. Goats and sheep do not appear to be susceptible to natural infection.
EHD clinical disease in WTD can be subclinical, hyperacute, acute, or chronic. EHDV nucleic acid can be detected by qPCR or EHDV can be isolated in the subclinical form, but clinical signs and macroscopic and microscopic lesions are absent and death does not occur. In the hyperacute form, sudden death is the outcome. Swelling of the head, neck, tongue, and eyelids can be observed in the acute form. In this form, there is fever, depression, anorexia, weakness, respiratory distress, ptyalism, ulceration of the oral mucosa, swelling of the tongue and eyelids, subcutaneous edema of the head and neck and lameness. Death may occur 1 to 3 days after the initial clinical signs. The chronic form is characterized by weight loss, coronitis, cracks in the hoof, and lameness. In some animals, the hoof sloughs off resulting in prostration or knee-walking. In the chronic form, affected deer may show symptoms for several weeks but generally recover.
Gross lesions in the hyperacute and acute forms, include hyperemia of the sclera, conjunctiva and oral mucosa and severe subcutaneous edema in the head, neck and limbs. There may be swelling and mucosal ulceration of the tongue. Widespread petechiae and ecchymoses are common in mucus membranes, subcutis and internal organs including the heart and gastrointestinal tract. Severe pulmonary congestion and edema are common. Erosions and ulcerations of the rumen and omasum are observed in some cases. In some affected animals, straw-colored fluid is present in the pericardium and paint-brush hemorrhages may be seen in the epicardium and papillary muscles. The main microscopic lesions consist of disseminated vascular necrosis and vasculitis with thrombosis, multifocal areas of hemorrhage and ischemic necrosis in various organs.
The differential diagnoses of EHD in WTD includes BTV, malignant catarrhal fever (MCF) and adenovirus infection. In cattle, it can be confused with other vesiculo-ulcerative diseases such as foot and mouth disease (FMD), vesicular stomatitis (VS), bovine viral diarrhea (BVD) and malignant catarrhal fever (MCF).
Serum is used for the detection of EHDV antibodies by the AGID test, virus neutralization or ELISA. EHDV can be isolated in cell culture from heparinized blood and from the spleen and other blood-rich tissues. Numerous real-time RT-PCR formats for the detection and serotyping of EHDV are used in diagnostic laboratories.
In the United States, there are no commercially available vaccines to prevent EHD. The use of autogenous EHDV inactivated vaccines is permitted in the US. Two doses, or in some cases one dose, of inactivated vaccine can provide considerable immunity to EHDV. However, there is a need for effective, DIVA vaccines (Differentiating Infected from Vaccinated Animals) to combat anticipated future incursions, as existing vaccines have inherent deficiencies.
For questions about this article, contact Dr. Andres de la Concha. To learn more about TVMDL’s test offerings, visit tvmdl.tamu.edu or call 1.888.646.5623.
de la Concha-Bermejillo. Epizootic hemorrhagic disease virus. In Backwell’s Five-Minute Veterinary Consult – Ruminant. E. McKenzie. Consulting Editor. Willey Blackwell. Second Ed. pp 325-326, 2017
Maclachlan NJ, Zientara S, Wilson WC, Richt JA, Savini G. Bluetongue and epizootic hemorrhagic disease viruses: recent developments with these globally re-emerging arboviral infections of ruminants. Curr Op Virol 34:56-62, 2019.