Schmallenberg is a viral infection found in cattle, sheep and goats. The virus is spread from animal to animal by midges, with peak transmission of the virus usually occurring in late Summer or early Autumn when midge numbers are at their highest. However, given the abnormally warm Autumn and early Winter and the subsequent prolonged survival of midges, it is likely that transmission continued for longer than normal last year.
Following infection, adult cattle can show clinical signs including diarrhoea, fever, and milk drop. However, Schmallenberg causes the most detrimental effects when pregnant animals are infected. Cattle are most susceptible to infection from days 60-180 of pregnancy, with sheep being susceptible from days 25-50. If animals are infected before these stages early embryonic death occurs and animals may come back on heat.
The virus damages the nervous system of the developing foetus, resulting in severe brain and spinal cord abnormalities. Lesions of the brain and spinal cord lead to secondary muscular and skeletal deformities. The most common deformities observed are persistently fused/flexed joints (arthrogryposis), a twisted neck/spine and a domed head. Offspring are usually dead but can be born alive. Calves/lambs/kids can appear normal in appearance but display nervous signs such as an inability to stand or suck, incoordination, and blindness, and require euthanasia. It is possible for one of a set of twins or triplets to be affected with the others being normal.
Cows and ewes often have trouble giving birth due to deformed offspring, and great care must be taken when assisting these births as if excessive force is applied, severe damage to the mother is inevitable. Veterinary assistance is often required in such cases, and deformed offspring often need to be delivered by caesarean section.
Unfortunately, it is difficult to prevent the disease, as there is currently no vaccine available. However, following infection animals gain immunity. Cycles of disease are seen in the UK every 4-5 years when naïve animals are infected by midges.
Synergy has already diagnosed Schmallenberg in calves, lambs, and kids this year. The APHA are currently offering free of charge Schmallenberg testing, so if you suspect the disease on your farm contact us to get some samples taken.
Written by: David Deane, Veterinary Surgeon
