Schmallenberg virus

Background

Between August and October 2011, outbreaks of disease in adult cattle that included mild to moderate fever, reduced milk yield, loss of appetite, loss of body condition and diarrhoea were reported in both the Netherlands and Germany. Testing for common causes proved negative.

From December 2011, abortion and stillbirths associated with foetal abnormalities, affecting mainly sheep but also cattle and goats, were identified in the Netherlands, Germany and Belgium.

A new virus was identified in November 2011 as the cause of both conditions. This was named ‘Schmallenberg virus’ (SBV) after the German town where the virus was first identified.

In early 2012, the first cases were suspected in the south and east of England. In these initial cases, the disease was diagnosed following the testing of deformed lambs. Since then, the disease has been diagnosed across a large area of Southern and central England, in affected lambs and calves.

Schmallenberg virus is in the Simbu serogroup of the Orthobunyavirus group. This group of viruses includes many different viruses which occur in Asia, Africa and Australia, but have not previously been identified in Europe.

As this is a newly identified virus there are still aspects of the disease that remain unknown at this point until more research has been done.

The disease is widely distributed in Europe. The annual sheep and goat Brucella survey offered AHVLA scientists an opportunity to conduct additional surveillance for Schmallenberg virus on sheep in counties where infection had not been detected. Tests on samples collected during the sheep and goat Brucella survey indicated that Schmallenberg virus had spread during the 2012 active midge season to cover previously unaffected areas, including parts of northern England and Wales.

Currently we know that the virus can infect and cause disease in sheep, cattle and goats. We would also recommend that keepers of exotic or wild ruminants, such as the camelid (alpacas, llamas) and cervid families (deer) are vigilant.

Transmission

Orthobunyaviruses are typically primarily spread by biting insect vectors, such as midges and mosquitoes, although the routes of Schmallenberg virus transmission have not yet been confirmed. The potential for direct transmission (i.e. direct from one animal to another) is therefore, as yet, unknown.

If biting insect vectors are the major route of transmission, significant spread is believed less likely during the winter period when biting insects are usually much less active.

Research work suggests that live infected animals have virus in their blood stream for two to five days, when biting insects may acquire the virus which they can then transmit to another susceptible animal during blood-feeding.

It is believed Schmallenberg virus was circulating widely in sheep and cattle in the Netherlands and in a part of western Germany between August and October 2011.

It is likely that initial introduction of the virus to the UK resulted from wind-blown insect vectors originating in Europe.

Ruminants in the south, south west and east of England and imported ruminants and their offspring, are currently at the highest risk of showing signs of the disease, which at this time would be manifest particularly as birth of offspring with deformities or neurological signs. Other regions including the midlands and south Wales were at medium risk of midge incursion during the summer and autumn 2011 and therefore farmers in these areas are also requested to be vigilant for Schmallenberg virus associated problems in their livestock.

AHVLA has identified SBV infection in deformed lambs and calves in every month since January 2012. This suggests that some limited transmission, probably via native GB midges, has continued throughout the less active vector season. Therefore, this may potentially provide a reservoir from which new cases occur in 2012.

As the virus can localise in the tissues of foetuses, it is uncertain as to whether there was any potential for live actively infectious lambs, calves and goat kids to have been born in the spring, which could contribute to the spread of the infection this year.

Clinical signs and post mortem findings

Two clinical presentations have been observed due to Schmallenberg virus infection.

Adult animals
In adult cows the acute infection resulted in diarrhoea, fever, a reduction in milk yield, with a full and rapid recovery over several days.

Affected herds had outbreaks of disease lasting two to three weeks, but the possibility of a different epidemiological presentation occurring should be considered. In other species this stage of the disease has not been noted. Clinical signs have not been reported in adult or growing sheep, although there is anecdotal evidence of milk drop in milking sheep in Netherlands.

Newborn animals and foetuses 
The second presentation of the disease is associated with abnormalities in animals born alive or dead at term or aborted following infection of the dam, affecting mainly sheep but also cattle and goats. Malformations observed to date include bent limbs and fixed joints (arthrogryposis), twisted neck or spine, a domed appearance to the skull, short lower jaw and brain deformities (spaces filled with fluid in cerebral hemispheres, abnormally small parts such as cerebellum and brainstem) and marked damage to the spinal cord.  Some animals are born with a normal outer appearance but have nervous signs such as a ‘dummy’ presentation or blindness, ataxia, recumbency, an inability to suck and sometimes convulsions. The foetal deformities vary depending on when infection occurred during pregnancy.

It is important to note that field evidence from England and Europe has shown that many animals have been infected with Schmallenberg virus without any clinical signs being detected. Typically, the impact in most affected herds or flocks has been low, although a small number of farms have reported more significant losses. Other related orthobunyavirusesstimulate a strong immune response, which protects infected animals from subsequent ill effects. This means that they do not usually give birth to further deformed offspring. It is expected that Schmallenberg virus will behave in a similar manner, although there is inevitable uncertainty as this is a new disease.

Risk to humans

A Europe-wide risk assessment has concluded that Schmallenberg virus is very unlikely to cause illness in people. No human cases have been detected in any country, and the most closely related viruses only cause animal disease. A risk assessment produced jointly by the European Centre for Disease Prevention and Control (ECDC), the Robert Koch Institute (RKI), Germany, and the National Institute of Public Health and the Environment (RIVM), Netherlands, concluded that “it is very unlikely that SBV poses a risk to humans”. Please see the Health Protection Agency website for more information.

Farmers and veterinary surgeons are advised to take sensible hygiene precautions when working with livestock and abortion material. Although several members of the group of related viruses can affect humans, the ability to do so is thought to be due to a gene sequence which is not present in Schmallenberg virus.

Pregnant women should not have contact with sheep and goats at lambing/kidding time due to risks of exposure to other disease causing organisms.

Information for visitors to farms

Visitors to farms are advised to adopt the usual hygiene precautions for farm visits, such as washing of hands after touching animals and particularly before eating. Pregnant women are potentially at risk of acquiring a range of infectious diseases from animals, and should follow existing Defra guidance that advises them to avoid close contact with animals (including sheep, cows and goats) that are giving birth. This includes:

• avoiding contact with newborn or aborted lambs, calves or kids
• avoiding handling clothing or boots that may have come into contact with these animals
• ensuring that partners take appropriate hygiene precautions

Diagnosis

Disease suspected in newborn animals or foetusesThis is not a notifiable disease, it is advisable for farmers to consult their veterinary surgeon if they encounter cases of ruminant new borns or foetuses which are stillborn, show malformations or are showing nervous disease and you suspect Schmallenberg virus infection. Veterinary surgeons may contact their AHVLA/SAC laboratory if they require advice on sampling for diagnosis.

Acute disease suspected in adult cattleIf acute Schmallenberg infection is suspected, your veterinary surgeon may contact the local AHVLA/SAC laboratory for advice on sampling for diagnosis. This will usually involve taking EDTA blood samples for detection of the virus at the time of clinical signs, and clotted blood samples for the detection of the virus at the time of clinical signs, and clotted blood samples for detection of antibody in the acute phase of disease, and again 2-3 weeks later, to demonstrate seroconversion.

Advice for veterinary surgeons

• Suspect cases in foetuses or newborn animals will be sampled for histopathological, serological and virological examinations as appropriate.  Confirmation of infection is currently by detection of virus sequences using real time PCR on tissues.
• An indirect ELISA test for antibodies to Schmallenberg Virus (SBV) is available for use in cattle, sheep and goats. This test has been validated by AHVLA. A positive result indicates previous exposure but will not determine when this occurred. This test is available on a commercial basis at a cost of £6.20 per sample, and a turnaround time of 7 days.
• If cases occur outside laboratory working hours, please keep samples and carcasses chilled until they can be submitted for testing.

Treatment and control

On 21 May 2013 the Veterinary Medicines Directorate (VMD) licensed the veterinary pharmaceutical company MSD Animal Health to provide a vaccine for Schmallenberg virus. The vaccine, ‘Bovilis SBV’, should be available for use across the UK in summer 2013. Farmers are advised to speak to their veterinary surgeon if they wish to make use of, or find out more about, the vaccine.

Malformations affecting lambs and calves exposed to the virus in pregnancy may lead to birthing difficulties. Excessive force must not be used during the birthing process as this may risk injury to both the dam and offspring. Farmers should contact their veterinary surgeon in those cases which cannot be delivered naturally.

It is important that strict hygiene measures are carried out during assisted lambings and calvings.

Embryotomy (dissection and removal of a foetus that cannot be delivered naturally) should only be carried out on dead foetuses by operators competent to carry out the procedure. It should never be used to remove a live foetus.

AHVLA Regional Laboratories have reported severe abnormalities in some live born lambs and calves. They are visibly distressed and unlikely to survive or thrive long term. You should consider as soon as possible, and in liaison with your private veterinary surgeon as required, if any offspring deformities are likely to result in any immediate or long term welfare problems during rearing. Euthanasia may be required in severely affected lambs and calves and additional support and care may be required during the rearing period for less severely affected newborns. You should also consider whether any abnormalities will affect the animals’ intended future use and fitness for transport in the long term.

Since SBV is not a notifiable disease there are no movement restrictions. Current knowledge suggests that acutely infected animals carry the virus during this period of viaraemia.

Control of midges is unlikely to be effective given that they are very widespread, and appear to be very effective at spreading SBV.

From Defra Website.