Spring 2025 Schmallenberg update
Although cases of disease caused by Schmallenberg virus have been reported in England in previous years, Scottish herds and flocks have remained largely unaffected until 2025. Cases have been reported in early lambing flocks this spring in the Southwest and the central belt of Scotland with evidence of exposure being more widespread.
What is Schmallenberg disease?
Schmallenberg disease is caused by a virus and is spread by midges. A midge must bite an infected animal followed by an uninfected one to transmit disease; animal to animal transmission is not possible. Following infection, cattle or sheep may show a mild illness for a few days; fever, diarrhoea, milk drop, loss of appetite. The most dramatic effects of Schmallenberg virus are seen when an animal is infected at critical stages of pregnancy. Infection between days 28-40 of pregnancy in sheep and 3-6 months of pregnancy in cattle allows the virus to cross the placenta to the developing foetus. The effects of this are seen at term when lambs or calves may be born with obvious deformities. Fused joints and twisted necks or spines are the most common deformities seen. This will often make lambing/calving much more difficult. So if a ewe/cow appears to be struggling to give birth, examine her ASAP and if the lamb/calf feels strange, contact your vet ASAP. Although caesareans are expensive, the loss of a ewe /cow will be much greater. In some cases, alongside deformities, lambs are reported to be poorly muscled, weak and unable to suckle and some may have neurological signs. Infection before the critical period in pregnancy may cause early abortion and reabsorption resulting in a higher barren rate at scanning.
What can I do about it?
For flocks and herds lambing and calving at the moment, the critical period of exposure is likely to have been July to September 2024 although a mild autumn may have led to prolonged midge exposure into November, having the potential to impact flocks and herds further into the spring. Schmallenberg disease is not notifiable but we are keen to track areas of the country that have been affected. If you are suspicious your stock has been exposed please get in touch with your vet who can sample affected foetuses or blood sample dams. It is worth remembering that blood sampling dams will only indicate exposure; the timing of exposure is key as to whether offspring will be affected and often the timing of exposure may be unknown. Exposed stock do develop immunity which is thought to last several years therefore offspring will be unaffected the following year; this will include maiden stock if an antibody response to exposure has been demonstrated on blood samples.
Bluetongue virus (BTV) is also spread by midges and, unlike SBV is notifiable. There have been no reports of incursion into Scotland and continued surveillance relies on vets being informed of any suspicion. Symptoms of BTV include abortion, crusting of the nose, salivation and lameness.
It is also important to remember that there are other known causes of deformities and perinatal mortality and a diagnosis of SBV should not be made without confirmatory laboratory testing. An accurate diagnosis is essential to decide what interventions are necessary to increase lamb and calf survival in both this and future years.
By VIO Megan Fergusson.
Posted by SRUC Veterinary Services on 11/03/2025
