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Editorial Information

Schmallenberg Virus (SBV)


Background

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 resulted from wind-blown insect vectors.

Disease in the UK

On January 23 SBV was reported on four sheep farms in Norfolk, Suffolk and East Sussex.  In these initial cases, the disease was diagnosed following the testing of deformed lambs.

Up to March 5 2012 Schmallenberg virus (SBV) infection has been identified on 121 farms. Eight of the positive cases have been diagnosed in cattle, 113 in sheep, and none to date in other species. Four new counties have reported disease: Devon, Dorset, Cambridgeshire and Somerset. So far, none of the affected farms have reported importing animals during 2011.

Cattle and sheep in the south, south west and east of England are currently at the highest risk of showing signs of the disease; at this time this 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.

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.

Treatment and control

Malformations affecting lambs exposed to the virus in pregnancy may lead to lambing difficulties. Excessive force must not be used during lambing as this may risk injury to both the ewe and lamb. Farmers should contact their veterinary surgeon because safe delivery may necessitate a caesarean operation. Lambs delivered alive with severe deformities must be euthanased for welfare reasons.

There are no published reports regarding specific calf abnormalities caused by Schmallenberg virus but anecdotal reports describe calving difficulties caused by fused joints necessitating embryotomy or caesarean operation.  Farmers must be aware that these abnormalities may arise whereby joints cannot be flexed to correct the position of the calf's legs. In the image below the joints of the hindlegs are fused and the legs are extended alongside the abdomen such that all four feet are presented together.  Excessive traction must be avoided in an attempt to deliver the calf because this will only result in rupture of the uterus and death of the cow.  The calf below (a schistosoma reflexa abnormality) was delivered by caesarean operation.  Such surgeries are not routine because of difficulties in manipulating the calf within the womb and the length of the uterine incision.  Farmers must be aware that any calving problem may be the result of fused joints caused by SBV and that delivery by caesarean operation may be indicated but this is not a routine surgery and is often complicated and more difficult than usual; early veterinary invention is essential.

fig1

A schistosoma reflexa abnormality causing calving difficulties; such fused joints may also be caused by SBV.

There is no treatment or vaccine currently available for this disease. Other SBV-related diseases include Akabane virus.  Knowledge of this virus may help identify potential SBV infection in the UK.

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. 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.

Akabane disease

Akabane disease is a disease of cattle, sheep and goats, spread by Culicoides spp. midges. Infection of pregnant animals results in foetal infection leading to abortions, stillbirths, dystocia and, most notably, serious and often fatal congenital abnormalities of newborn animals.  Outbreaks of disease appear as arthrogryposis (contracted tendons) and hydranencephaly (brain defect of the cerebrum and cerebellum) in newborn calves and lambs.

Contracted tendons in lambs and calves will be readily recognized by farmers but there are several causes, not least a genetic cause so farmers must report cases of contracted tendons to their veterinary surgeon or AHVLA.

Recognising brain defects will prove more challenging not least in calves where cerebellar hypoplasia and hydranencephaly are not uncommon birth defects caused by in-utero infection by bovine virus diarrhoea virus (BDVv).  Affected newborn calves will have difficulty rising and typically stand with the legs held wide apart and the head lowered.  The calves are inco-ordinated when walking.  Calves with hydranencephaly show the above clinical signs but are also blind.

Potential diseases causing similar signs to SBV in calves

  • Bovine virus diarrhoea virus (BDVv) - present at birth.
  • Intracranial haemorrhage   as a consequence of dystocia - present at birth.
  • Hypoxia as a consequence of dystocia - present at birth.
  • Bacterial meningitis - appears at 3-7 day-old.

 

fig7

Calves affected with SBV-induced brain defects would be expected to show signs of low head carriage, wide-based stance, inco-ordination, and possibly blindness from birth.

fig2

Signs of low head carriage, ataxia and wide-based stance are commonly seen in congenital BVDv infection.

fig8

Calf affected by hydranencephaly.  This calf showed signs of low head carriage , ataxia and wide-based stance but was also blind from birth. (see below).

fig6

Hydranencephaly (see above) at necropsy.  There is little cerebral cortex and cerebellum - the common reported defects for Akabane infection, and most likely SBV.

Potential diseases causing similar signs to SBV in lambs

  • Congenital swayback- present at birth.
  • Border disease- present at birth.
  • Toxoplasmosis - present at birth.
  • Intracranial haemorrhage as a consequence of dystocia - present at birth.
  • Hypoxia as a consequence of dystocia - present at birth.
  • Dandy-Walker syndrome - present at birth.
  • Starvation/exposure/hypothermia - occurs from 6-12 hour-old
  • Septicaemia -  appears at 1-3 day-old
  • Bacterial meningitis  -  appears at 3-7 day-old

fig3

Newborn lamb affected by Dandy-Walker syndrome.  The clinical signs (if born alive) would be similar to SBV.

SBV-affected lambs will be affected at birth and have difficulty rising and typically stand with the legs held wide apart and the head lowered.  The lambs are inco-ordinated when walking (cerebellar hypoplasia).  Lambs with hydranencephaly show the above clinical signs but are also blind.

fig4

Septicaemia in day-old lamb.  Onset of clinical signs would differentiate from congenital SBV infection.

Public health

Schmallenberg Virus is not a notifiable disease but farmers and vets should remain vigilant and report any suspicious cases to AHVLA for testing as part of our enhanced surveillance. The European Centre for Disease Prevention and Control suggests that there is a low likelihood of any risk to public health.

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