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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’ 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.

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.

Geographical distribution

The disease is widely distributed throughout Germany, the Netherlands, and northern and Central France and has been detected in England, Italy and Luxembourg. See the summary of the latest situation in the UK.

Species affected

Currently we know the virus will infect and cause disease in sheep, cattle and goats. We would also recommend that keepers of exotic and wild ruminants, such as the camelid and cervid family (alpacas, Ilamas and 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 unlikely during the winter period when biting insects are usually inactive.

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.

Clinical signs

In adult cows, cases of acute infection have 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. In other species this stage of the disease has not been noted.

Clinical signs have not been reported in adult or growing sheep, atlhough there is anecdotal evidence of milk drop in milking sheep in Netherlands.

In newborn animals and fetuses, the disease is associated 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 include bent limbs and fixed joints, brain deformities 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 fits. The foetal deformities vary depending on when infection occurred during pregnancy.

Risk to humans

At the moment, a Europe-wide risk assessment has concluded that Schmallenberg virus is unlikely to cause illness in people. As yet, no human cases have been detected in any country, and the most closely related viruses only cause animal disease.

However, as this is a new virus, work is ongoing to identify whether it could cause any health problems in 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 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.

Treatment and control

There is no treatment or vaccine currently available for this disease. As this is a new disease further work is needed to determine what control measures may be appropriate. 

Diagnosis

This is not a notifiable disease, but farmers are asked to contact their veterinary surgeon if they encounter cases of ruminant neonates or fetuses which are stillborn, show malformations or are showing nervous disease. Veterinary surgeons should then contact their AHVLA/SAC laboratory if they suspect infection with the virus.  

Suspect cases will be sampled for histopathological and virological examinations.  Confirmation of infection is by detection of virus sequences using real time PCR on tissues. There is currently no serological (blood) test available but work is in progress to develop one.