Cattle farmers must remain vigilant for the signs of Schmallenberg virus as further cases are expected in the coming months, say scientists.
The latest figures from the Animal Health and Veterinary Laboratories Agency (AHVLA) show a slight fall in the number of positive cases of the disease in sheep, as the lambing season is now well under way.
So far, there have been 213 positive cases identified in sheep, but only 25 in cattle. Confirmed cases have been largely confined to southern and eastern counties in England.
However, the AHVLA is warning cattle farmers in particular to look out for symptoms of the virus in adult cattle, including fever, milk yield reduction, and diarrhoea.
In pregnant cattle, infection of the fetus may result in abortions, fetal malformations or stillborn calves.
Trevor Drew, head of virology at the AHVLA, said: "We are starting to see a slight drop in the number of cases in sheep.
"But it's too early to say we are out of the woods now. We mustn't forget that the disease also infects cattle and their pregnancy is twice as long as in ovine.
"Therefore, it's possible that we will start to see more positive cases in bovine in the coming months, more likely in the south. We expect this period could extend to as late as May."
Scientists believe that virus reached infected livestock in the UK via midges blown over from continental Europe during the summer and autumn of 2011.
"So far, we have seen no evidence of infection in 2012, but we need to be alert to this possibility," said Prof Drew.
"The big question is: has the virus overwintered? Farmers need to be alert to the clinical symptoms - both in cattle and sheep - and continue to report suspected cases to the AHVLA to allow us to assess the impact of the disease and make decisions."
At present, the disease is non-notifiable in Europe, and therefore there is no legal requirement for producers to notify the authorities of an outbreak - and a vaccine is probably at least a year away.
However, this week Germany joined The Netherlands in applying notifiable status to the virus.