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SMC(UK) Fact Sheet on Schmallenberg virus

Posted in Briefings on March 2nd, 2012.

This fact sheet was produced by the SMC UK to give journalists a background on the Schmallenberg virus currently affecting livestock in the UK and Europe.

Background

  • Schmallenberg virus, aka SBV, is an emerging livestock disease that has been detected in Belgium, Germany, the Netherlands, France, Italy, Luxembourg and the UK.
  • Outbreaks of disease in adult cattle and birth complications in cattle, sheep and goats were reported between August and November 2011 in both the Netherlands and Germany.
  • A new virus was identified in December 2011 as the cause of both conditions, named ‘Schmallenberg virus’ after the German town where the virus was identified.
  • In early 2012, the first cases were suspected in the south and east of England, diagnosed following the testing of deformed lambs.

The Virus

  • The Schmallenberg virus is of the family Bunyavirus, genus Orthobunyavirus.
  • Several viruses in the genus cause diseases in cattle and are transmitted by insects.
  • Schmallenberg virus is in the Simbu serogroup of the Orthobunyavirus genus, which includes many different viruses that occur in Asia, Africa and Australia, but have not previously been identified in Europe.
  • Genetic characterisation has shown that SBV is closest to several viruses known to be pathogenic in animals.
  • Shamonda, Aino and Akabane viruses in the Simbu serogroup are known to cause subclinical infections in a large proportion of infected animals.
  • There is no evidence that the Schmallenberg virus causes disease in humans (see Public health risk).
  • There is no vaccine for the SBV at this stage.

Detection

  • Initial microbiological investigations of infected animals proved negative, however advanced techniques revealed novel genetic sequences, which were also detected in tissues from stillborn and deformed newborn animals.
  • The SBV can be identified using several methods, some based on its genetic sequence and some based on its specific interactions with antibodies: These tests do not allow for large scale surveillance and no timeline is available for obtaining a test suitable for mass surveillance.
  • The ‘viraemic period’ for which the virus is present in the bloodstream is thought to be short (4-6 days post-exposure) which can make the identification of the pathogen in adult live animals problematic.
  • The virus is present for a longer time in infected foetuses and can be detected in malformed newborns.

The Disease

The Schmallenberg virus causes brief, mild to moderate disease in adult cattle, and life threatening defects in cattle, sheep and goats in utero. For adult cattle populations, outbreaks of disease last two to three weeks.

Clinical Signs:

  • Adult cattle: reduced milk yield (up to 50%), fever, loss of appetite, loss of body condition and diarrhoea.
  • Newborn/foetal livestock: late abortion, stillbirths or major birth defects including 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 (loss of full control of bodily movements), recumbency, an inability to suck and sometimes fits. The foetal deformities vary depending on when infection occurred during pregnancy.

Transmission:

  • It is likely that the virus is transmitted via Culicoides midges, though this is as yet unconfirmed.
  • The potential for direct transmission (i.e. direct from one animal to another) is as yet unknown, though it is clear the virus can be transmitted across across the placenta.

Immunity:

  •  Immunity can possibly be acquired naturally against SBV.
  • It is possible that the seasonality of the infection cycle would not entail a second epidemic circulation next year. This is supported by the shortness of the viraemic period.
  • Vaccination could be an option for controlling the disease, and a vaccine exists for the similar virus Akabane.

Public health risk

  • There is unlikely to be a risk to human health from Schmallenberg virus; but this is not yet certain (see European Commission risk assessment below). No human cases have been detected in any country.
  • The ability to infect humans is thought to be due to a gene sequence which is not present in Schmallenberg virus, and those viruses most closely related are not ‘zoonotic’ – i.e. the disease cannot pass from animals to humans.

Sources / further information

Defra website, with links to periodic outbreak assessments

The Animal Health and Veterinary Laboratories Agency, with updated figures of infection numbers by county

Veterinary Laboratories Agency

Health Protection Agency, includes a Q&A

European Commission documents, including a risk assessment for public health

The Friedrich-Loeffler-Institute who initially identified SBV, including fact sheets and Q&A

World Organisation for Animal Health fact sheet

This is a fact sheet issued by the Science Media Centre to provide background information on science topics relevant to breaking news stories. This is not intended as the ‘last word’ on a subject, but rather a summary of the basics and a pointer towards sources of more detailed information. These can be read as supplements to our ‘round-up’ press releases.

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