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Although it is currently quiet around the bluetongue virus in the Netherlands, livestock farmers are actively preparing for a possible new outbreak. Both sheep and cows are vulnerable, but the virus behaves differently for each species. For now, vaccination seems to be the main means of preventing mortality. We speak to Reinard Everts and Margit Groenevelt about bluetongue in cows and sheep.

After a fierce outbreak of the bluetongue virus in 2023, and a resurgence of the disease in 2024, livestock farmers and vets are holding their breath as temperatures slowly rise. ‘At the moment it is still calm,’ says vet Margit Groenevelt, who specialises in sheep. "The midges that spread the virus are waking up, but it is not yet warm enough to see them in large numbers. Still, we know: the virus is not gone. It is overwintering."

The bluetongue virus is transmitted by midges, small mosquito-like insects. They transmit the virus from animal to animal. The new midges now hatching from their eggs are still virus-free by themselves. But as soon as they meet an infected animal, they can spread the virus further.

Big differences between sheep and cows

According to veterinarian and researcher Reinard Everts, it is important to understand the distinction between animal species. "For sheep, the virus is often fatal. For cows it is less fatal, but it can make them seriously ill. Think lameness, fertility problems, drop in milk production and even abortion." Another important difference: cows can carry the virus for much longer than sheep. "Sometimes the virus is even transmitted to the calf in the womb. That calf is then born with the virus in its blood. And as soon as a knut sucks on that, the spread continues."

Vaccination is essential

Despite the relative calm at the moment, many livestock farmers have already started vaccinating. ‘Last year in particular, there was a lot of focus on vaccinating sheep,’ says Groenevelt. "Logical, because that's where we saw the most mortality. But vaccination remains the most effective way to prevent mortality and serious disease even now."

Everts concurs: "The cow plays an important role in maintaining the virus. Because of their long duration of infection and the risk of transmission to calves, they are crucial in the spread cycle. And although they are less likely to die of bluetongue, they can cause serious economic damage to farmers."

Preference for cows

Midges seem to have a clear preference for cows. ‘Why exactly we do not yet know,’ says Everts, ‘but possibly cows are more attractive because they are bigger or because, unlike sheep, they do not have a thick woolly coat.’

Looking ahead

The next few weeks should reveal whether there will be another bluetongue outbreak, and how much damage it will cause. If temperatures rise and the midge population increases, the bluetongue virus could just strike again. Livestock farmers hope their preparations are sufficient to prevent a repeat of last year.

As a livestock farmer, what is the best thing to do at the moment? Groenevelt: "The best measure cattle farmers can take at this moment is still to vaccinate the animals. That remains the most effective way to prevent mortality and severe disease."