Bluetongue virus (BTV-3) affects cattle, goats, sheep, deer and camelids such as llamas and alpacas.
It can cause ulcers or sores around the animal’s mouth and face, difficulties swallowing and breathing, fever and lameness, foetal deformities and stillbirths.
The latest outbreak began in the Netherlands in 2023, where tens of thousands of sheep died, and midges blown over from the continent began infecting livestock in the south-east of England too.
But the impact of BTV-3 seems to vary considerably across different regions, with some animals showing little sign of infection and managing to recover.