Nationwide Distribution and Prevalence of Epizootic Haemorrhagic Disease Virus Infection in Portugal (2023-2025)

Epizootic haemorrhagic disease virus (EHDV) is an insect-borne virus that affects ruminants. It has recently emerged as a significant threat to livestock and wildlife, particularly deer and cattle. Since its introduction into Europe in late 2022, severe outbreaks have been reported across several European countries, including Italy, Spain, France, and Portugal. The first confirmed circulation of EHDV in Portugal was reported in July 2023, involving serotype 8 (EHDV-8) in cattle from the municipalities of Moura and Barrancos, in the Beja district of the Alentejo region, alongside concurrent circulation in cervids. Here, we analyse the prevalence and spatial distribution of EHDV during the first recorded outbreaks in Portugal (2023-2024), describing its geographic spread across the country and subsequent disappearance by 2025. Higher viral loads were significantly associated with the presence of clinical signs. These findings provide new insights into the epidemiology of EHDV infection and suggest that higher viral loads are associated with the occurrence of clinical disease in naturally infected animals.