As the spring lambing and calving period comes to an end, there have been many reports across the UK of deformed lambs and calves suggestive of in utero infection with Schmallenberg virus (SBV).
First identified in 2011 in North-West Germany and the Netherlands, this virus causes disease in sheep, cattle and goats.
SBV is spread by the Culicoides midges, which are widely present across Europe and move easily between farms and regions allowing rapid and extensive spread of infection.
The spread of infection therefore occurs predominantly when biting midges are most active between May and October. With mild winter conditions however midge activity may extend into November and early December.
As of March 2017 the Animal Health and Plant Agency (APHA) have confirmed SBV in lambs on 84 premises in England, 25 in Wales, and in calves on three premises in England. Cases have been reported from Cornwall to as far North as Northumberland.
In Northern Ireland antibodies to Schmallenberg virus were detected in the first quarter of this year in two calves with skeletal deformities from two different herds and a cow from a herd experiencing abortions and calf abnormalities. Whilst an antibody positive does not confirm the involvement of the virus, it provides evidence that this virus is circulating again in Northern Ireland.
Other cases in Northern Ireland included a three-day-old calf born into a dairy herd which was presented for post mortem at AFBI laboratories with a cleft palate and severe limb and spinal deformities; and a term stillborn lamb submitted from a lowland flock in mid-February. At necropsy, severe abnormalities of all four limbs of the lamb were noted. There was very little movement in spinal column and the spinal cord was very narrowed. SBV was considered likely in both cases.
Many suspected cases of SBV however are not reported and confirmed, meaning we do not know the true extent of the problem.
SBV is now considered to be an endemic disease in the UK. Discussion around protection against SBV should therefore form part of the flock/herd health planning which farmers do with their vets who are in an excellent position to know what the SBV situation is within your area as many of the deformed lambs and calves will need veterinary intervention at lambing or calving.
What are the clinical symptoms of the infection?
Infection of non-pregnant sheep and cattle may go unnoticed but infection of naïve pregnant animals, especially during the most sensitive period can result in stillbirths or severe deformities of the foetuses and abortion.
Sheep are most sensitive between days 28-56 of pregnancy i.e. during the 2nd month of pregnancy.
Cattle are most sensitive between days 70-150 of pregnancy i.e. during the 3rd to 5th month of pregnancy.
Other clinical signs in adult cattle include fever, a drop in milk yield and diarrhoea.
With the main risk of transmission of infection being May to October most at risk are ewes or cows being served in summer and early autumn. For dairy herds because of the potential production losses in lactating animals there is clearly a risk throughout the active midge season.
How long does natural
Following infection animals become immune, but how long that immunity lasts is unknown, and not all animals in the herd or flock may be infected, meaning some remain naïve. Therefore even where losses are experienced this year it does not necessarily mean that the herd or flock is not at risk of further losses next year.
How can I protect my
Protection against Schmallenberg is through keeping susceptible animals away from the vector (the midge) and vaccination.
Research into the use of insecticides against the Culicoides midge species, found a deltamethrin-based pour on treatment to be an effective vector control method. In one study, even hair clipped from the feet of cattle 35 days after standard treatment contained enough deltamethrin to kill midges.
Fly & Lice Spot On™ contains deltamethrin and a vegetable oil carrier which ensures the active ingredient is spread over the whole body and kill is achieved in just two hours at all sites shown in Fig 1. When midges land on treated cattle or sheep their feet contact the Fly & Lice Spot On™ and the deltamethrin affects the midge’s nervous system leading to muscular excitement, paralysis and death.
Whilst vector control methods are an important part of a Schmallenberg Virus control strategy, and will certainly be useful at farm level, alone they are unlikely to be successful at controlling disease over a large area, because of the behaviour and movements of the midges.
Therefore vaccination alongside an effective insecticide is the most effective way to protect your flock/ herd against SBV.