Schmallenberg Virus (SBV)

Between August and October 2011, outbreaks of disease in adult cattle causing 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.

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.  Schmallenberg Virus is similar to some other animal disease pathogens including Akabane and Shamonda viruses, which are transmitted by vectors, such as midges, mosquitoes and ticks. Schmallenberg  virus can infect and cause disease in sheep, cattle and goats.

Schmallenberg virus transmission has not yet been confirmed. The potential for direct transmission (i.e. direct from one animal to another) is therefore 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 and Ireland resulted from wind-blown insect vectors.

Clinical Signs

In the Netherlands and Germany outbreaks of SBV disease in cattle have caused clinical signs including fever, reduced milk yield, inappetence, loss of body condition and, diarrhoea.  Outbreaks of disease have lasted 2-3 weeks, with individual affected animals recovering over several days. These clinical signs are broadly similar to another midge-borne viral disease familiar to UK livestock farmers - bluetongue.

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

In newborn animals and foetuses, 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. Persistent flexion of the joints (arthrogryposis or "contracted tendons") is reported to be a common birth defect.  However, arthrogryposis can also be inherited as an autosomal recessive condition therefore veterinary investigation is essential.  Some animals are born with a normal appearance but have nervous signs such as a 'dummy' presentation or blindness, ataxia, recumbency, an inability to suck, and sometimes seizures. 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.