Schmallenberg Virus in Cattle and Sheep

Schmallenberg Virus (SBV)

·         Background: (Autumn 2011 Germany and Netherlands) outbreaks of the disease were seen in cattle; causing fever, reduced milk yield, loss of appetite, loss of condition and diarrhoea. (Winter 2011 Germany, Netherland and Belgium) abortion and stillbirths associated with foetal abnormalities, affecting mainly sheep but also cattle and goats, were reported. The cause of both these conditions was attributed to a new virus discovered; the Schmallenberg Virus (SBV) named after the German town where it was first identified.
SBV is in the Simbo serogroup of the Orthobunyavirus group. This group of viruses included many different viruses which occur in Asia, Africa and Australia, but have never been seen in Europe before. SBV is similar to other animal pathogens including Akabane and Shamonda viruses; these other viruses are transmitted by vectors such as midges, mosquitoes and ticks. SBV can infect and cause disease in sheep, cattle and goats.
The transmission of SBV has not yet been confirmed. The potential for direct transmission 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 that SBV was circulating widely in the affected areas during late summer of 2011. It is likely that the introduction to the UK resulted from wind-blown insect vectors.

·         UK Outbreak: (January 2012) SBV was reported on sheep farms in the south east. In these cases, the disease was diagnosed following the testing of deformed lambs.
(March 2012) SBV infection had increased by massive amounts, all mainly in sheep. The disease had spread to the South and South West. Cattle and sheep in the South East, South and South West are at the greatest risk of infection. Midlands and Wales at medium risk.

·         Clinical Signs: (Cattle) In Netherlands and Germany, outbreaks of SBV disease in cattle have caused clinical signs including fever, reduced milk yield, inappetance, loss of body condition and diarrhoea. The outbreaks tend to last 2 – 3 weeks, with individual affected animals recovering over several days. The clinical signs in cattle are broadly similar to BTV, another midge-borne viral disease seen (rarely) in UK livestock.
(Sheep) Clinical signs have not been reported in adult or growing sheep; although there is anecdotal evidence of drop in milk yield of milking sheep in Netherlands. In new-born animals and foetuses, the disease is associated in animals born alive or dead or aborted following infection of the dam. The disease primarily affects 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 and so vet analysis is necessary to diagnose the SBV on this symptom. Some animals are born with a normal appearance but have nervous signs due to brain or spinal damage; such as blindness, ataxia, recumbency, inability to suck and sometimes seizures. The severity and type of deformities vary depend on the point at which the foetus was infected during pregnancy.

·         Treatment and Control: As lambs are often presented with malformations, lambing can be difficult for both the ewe and farmer. Excessive force must never be used during lambing of a difficult birth; this may risk injury to both the ewe and lamb. It may be necessary for a vet to perform a caesarean operation, resulting in deformed lambs being euthanized for welfare reasons.
In cattle there are no specific reports regarding calving abnormalities caused by SBV; there is anecdotal evidence reporting of calving difficulties caused by fused joints, necessitating embryotomy or caesarean operation. This means that the joints cannot be flexed to correct the position of the calf’s legs. Excessive traction/force will more often than not lead to a uterine tear or rupture, leading to the death of the cow. Often, caesarean options to deliver calves with fused joints are complicated, because of the difficulties in manipulating the calf in the womb and the length of the uterine incision.
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: A Europe-wide risk assessment has concluded that SBV is unlikely to cause illness in people. As yet, no human cases have been reported. As this is a new virus, work is ongoing to identify whether it could cause any health problems in humans. Those that work in close contact with the disease should 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 SBV. Pregnant women should avoid all contact with sheep and goats during lambing season.

Akabane Disease

This disease can affect sheep, goats and (mainly) cattle.

·         Spread by the Culicoides spp. midge. Infection of pregnant animals results in foetal infection leading to abortions, stillbirths, dystocia and serious congenital abnormalities of new-born animals.

·         Outbreaks of the disease appear as arthrogryposis (contracted tendons) and hydranencephaly (brain defect of the cerebrum and cerebellum) in new-born calves and lambs.  Contracted tendons will be readily recognised but there are several causes, not least a genetic cause; therefore farmers must report cases to a vet or AHVLA. Recognising brain defects will prove difficult in calves where cerebellar hypoplasia and hydranencephaly are not uncommon birth defects caused by in-utero infection by BVDv.

·         Affected new-born calves will have difficulty rising and typically will stand with a wide stance and head lowered. The calves are unco-ordinated when walking. Calves with hydranencephaly show the same signs but with added blindness.

In calves there are other diseases which present similar signs to SBV…
1) Bovine Viral Diarrhoea Virus – present at birth.
2) Intracranial haemorrhage; as a result of dystocia – present at birth.
3) Hypoxia; as a result of dystocia – present at birth.
4) Bacterial Meningitis – appears 3 to 7 days after birth.

In lambs there are other diseases which present similar signs to SBV…
1) Congenital swayback – present from birth.
2) Border disease – present from birth.
3) Toxoplasmosis – present at birth.
4) Intracranial haemorrhage; result of dystocia – present at birth.
5) Hypoxia; result of dystocia – present at birth.
6) Dandy-Walker syndrome – present at birth.
7) Starvation/exposure/hypothermia – appears from 6-12 hours old.
8) Septicaemia – appears at 1-3 days old.
9) Bacterial meningitis – appears 3-7 days old.

>SBV-infected lambs will be affected from birth and will have difficulty rising and typically stand with legs held wide apart and head lowered.

>The lambs are also un-coordinated when walking (cerebellar hypoplasia).

>Lambs with hydranencephaly show above clinical signs but are also blind.

Hydranencephaly or hydrancephaly is a condition in which the brain's cerebral hemispheres are absent to varying degrees and the remaining cranial cavity is filled with cerebrospinal fluid. Hydranencephaly is a type of cephalic disorder. These disorders are congenital conditions that derive from either damage to, or abnormal development of, the foetal nervous system in the earliest stages of development in utero. Cephalic is the medical term for “head” or “head end of body.” These conditions do not have any definitive identifiable cause factor; instead generally attributed to a variety of hereditary or genetic conditions, but also by environmental factors such as maternal infection, pharmaceutical intake, or even exposure to high levels of radiation.

This should not be confused with hydrocephalus, which is an accumulation of cerebrospinal fluid in the ventricles. In hemihydranencephaly, only half of the brain is filled with fluid.