Abstract Epizootic haemorrhagic disease (EHD) is a notifiable disease to the World Organisation for Animal Health caused by Orbivirus ruminantium (EHDV), closely related to bluetongue virus (BTV) and transmitted by Culicoides spp. In autumn 2022, EHDV serotype 8 (EHDV-8) was detected for the first time in Spain and Europe, affecting domestic and wild ruminants. Red deer ( Cervus elaphus ) were the most affected wild species, with reports of neurological signs, severe respiratory distress and mortality. Nevertheless, the pathogenesis of EHDV-8 in this species remains poorly understood. This study aimed to evaluate the clinical and pathological impact of EHD in red deer, characterising clinical signs, main lesions, tissue distribution and target cells of EHDV. Clinical data were collected through a nationwide online survey and field outbreak studies, and histopathological and immunohistochemical analyses were performed on 16 confirmed EHDV-8 cases. Frequent clinical signs included neurological signs, ptyalism, lameness and dyspnoea. During the outbreak, average morbidity and mortality in captive red deer were 6.9% and 4.9%, respectively, with a case fatality rate of 70.3%, higher in males and almost exclusively in adults. Gross examination revealed extensive vascular and epithelial lesions with generalised congestion, focal to multifocal haemorrhages and marked pulmonary oedema, confirmed histologically with severe cellular damage. The most affected organs were the brain, lungs, liver, kidneys and spleen, showing interstitial oedema, vasculitis, mononuclear infiltration with necrosis, severe lymphoid depletion and gliosis with satellitosis in the brain. The EHDV antigen was primarily detected in macrophages, reticular cells, endothelial cells and epithelial cells. This study provides the first description of EHDV’s clinical and pathological impact in red deer, confirming their high susceptibility to EHDV-8.
Muñoz-Fernández et al. (Wed,) studied this question.