Schmallenberg Virus (SBV): FAQs
What is Schmallenberg virus (SBV)?
Schmallenberg virus (SBV) is a novel Orthobunyavirus that has been associated with disease in ruminants (cattle, sheep and goats) in Europe. It is closely related to other viruses circulating in Africa, Asia and Australia (specifically the Akabane, Aino and Shamonda viruses), which are transmitted by biting insects and cause foetal deformities.
Insect borne viruses used to be restricted to tropical areas of the world, but now they are becoming an increasing problem further afield. Climate and ecological changes, increased livestock production and population migration are all factors thought to be contributing to the wider geographical spread of these types of viruses.
In Europe, SBV was first detected in Germany and has been named ‘Schmallenberg’ after the town where the first ruminant cases were identified.
What animals are affected by SBV?
Infection has been confirmed in sheep, cattle, goats (two cases in East Sussex reported at the end of February 2013) and alpacas (one case reported in Northamptonshire at the end of Feb 2013) in the UK. The virus has also been detected in roe deer, fallow deer, red deer, mouflon, bison and wild boar although no deformed fetuses have been reported in these species to date. There have been no confirmed cases in UK deer or wild boar.
What does the virus do to infected ruminants?
SBV causes transient clinical symptoms in adult cattle (eg. fever, diarrhoea, loss of appetite, milk drop etc.) and congenital malformations in newborn ruminants. The most notable effect of the disease is on the unborn foetus – the virus appears to affect the development of the skeleton and the nervous system.
In flocks and herds where SBV infection has been confirmed, abortion/mummified foetuses, still births, early births of stiff jointed/weak/deformed/unco-ordinated calves and lambs, and lambing/calving difficulties have all been reported.
To date infected adult sheep and goats have shown no signs of disease, but this may simply be because these animals are handled less frequently than cattle.
Is SBV a danger to humans?
It is unlikely. Studies have confirmed that there is no evidence of human infection when people have been working in close proximity to infected ruminant livestock. In Holland recently, 300 Dutch farmers were blood tested at a meeting and all were negative. No illness has been reported to date in humans.
Is there any danger from eating dairy, meat and venison?
There is no risk based on current knowledge.
How is SBV spread?
Observational studies have revealed that the virus is transmitted via insect vectors, mainly midges. The virus has been identified in pools of heads of the Culicoides obsoletus and Culicoides dewulfi midge species. Midge trapping studies in Holland have now shown that the proportion of insects carrying the SBV virus is 10 times greater than was the case with the Bluetongue virus.
When did SBV arrive in the UK?
Cases started to be detected in the South East of the UK in January 2012. Analysis of weather records suggests the virus probably arrived when plumes of infected midges were blown across the English Channel during the second half of 2011. Since then the disease has spread right across England, Wales and to Ireland.
When is the peak disease risk period?
Animals are most at risk during the warmer months when infected midges are active. However, it is pregnant ruminant livestock that are most vulnerable and it is their unborn foetuses that bear the brunt of the worst effects of the disease. The peak risk period for foetal deformities in sheep is the first 28-60 days of pregnancy, while cattle have a longer and later risk period of between days 80-140 days of pregnancy. It is believed that infections before these periods may cause foetal death and abortion, but as yet there is no research data available to confirm this supposition.
What is the within flock/herd prevalence following natural infection?
This is unclear because midge populations, weather conditions and animal breeding seasons vary so much across the UK. In a recent letter to the Veterinary Record, only 25% of animals in a housed herd showed evidence of infection, yet only 7 miles away another dairy herd grazing outside during the summer showed 75% of the cows being infected. MSD Animal Health is currently working on studies with a number of UK veterinary practices to try and better understand this issue.
Can SBV be transmitted from animal to animal?
At the moment scientists don’t think so because SBV is very closely related to other viruses that need midges/mosquitos to transmit infection. However, recent studies have found that the virus is excreted intermittently in semen. At this stage, more research is needed to establish whether venereal disease transmission can occur.
How much of a threat is SBV to my ruminant livestock?
SBV is a highly significant threat on the majority of UK cattle and sheep farms because infected midges have ranged far and wide. The disease has spread very rapidly compared with Bluetongue, for example, because plumes of midges carry a heavy viral load. SBV has also been confirmed in Scotland, but only in animals that originated in England. However, cases are being identified further and further north. In fact, even ruminant livestock in Finland have now been infected.
How many SBV cases have been confirmed in the UK?
On February 27th 2013 the Animal Health and Veterinary Laboratories Agency (AHVLA) reported that SBV had been confirmed on 1,531 UK farms – a 26% increase on the figure reported in January 2013. However, there is widespread concern that SBV cases are being under-reported; mild clinical cases in adult cattle, for example, are easily missed. SBV has now been detected in every county in England and Wales.
How long are animals affected by SBV?
Infected animals are believed to carry the virus for a few days only. The virus is only detected in the bloodstream for 2-7 days and any disease symptoms (eg. fever, diarrhea, milk drop) are only visible for a short period of time. Adult cattle appear to recover quickly. It is possible that infection before mating may give good immunity with minimal impact on reproduction, but the immunity picture is far from clear at the moment.
How long does immunity last following natural infection?
It is to be hoped that once the virus had passed through a herd or flock then animals would have a good level of immunity for subsequent breeding seasons. But we really don’t know how long immunity lasts. Anecdotal evidence from mainland Europe shows strong protective immunity following natural exposure to the virus, but no trials have yet been done to establish the duration of this immunity. Most experts expect it to last for at least 12 months, which corresponds to the timeframe scientists have been studying this new virus.
How can I protect my livestock?
Until a vaccine becomes available and there is very little that can be done. Midge/fly control preparations are unlikely to prevent the first bites, which transmit infection. However, insecticides may help reduce local spread by preventing further blood meals. Other measures such as improved biosecurity, housing livestock and removing muck heaps to deny swarms of midges access to breeding habitats may help to reduce the disease threat.
It may be possible to reduce the impact of the virus in a flock or herd by delaying pregnancies. If the risk period of pregnancy occurs outside the midge season there is a reduced chance of problems in unborn foetuses. However, this strategy may not be practical on many farms.
What do I do if I suspect SBV infection in my herd or flock?
Be watchful at lambing and/or calving time and if you have any suspicions at all you should report unusual signs to your vet. Be aware that malformations affecting lambs and calves exposed to the virus during pregnancy may lead to lambing/calving difficulties. Do not use excessive force as this may injure both the newborn and dam. Ask your vet for help.
What diagnostic services are available?
If SBV is suspected your vet can blood test your herd or flock to establish whether animals have been infected. Detection of the virus in aborted fetuses and malformed lambs and calves can be done from brain and supplementary blood samples.
How soon will a vaccine be available?
MSD Animal Health isolated the Schmallenberg virus in 2012 and has developed a vaccine. The vaccine is based on wild-type SBV that has been inactivated and contains an adjuvant that stimulates the immune response. In studies to date, safety and efficacy has been demonstrated in cattle and sheep. The company is now working closely with the regulatory authorities but is not able to speculate as to when the new vaccine will be available.