Schmallenberg virus (SBV) is a novel Orthobunyavirus that has been associated with disease in ruminants (cattle, sheep and goats) in Europe. Antibodies were also detected in individual roe deer, red deer and one bison.
The disease causes transient clinical symptoms in adult cattle (fever, diarrhoea, reduced milk yield, etc.) and congenital malformation in newborn ruminants.
Genetic analysis of the Schmallenberg virus genome shows that this virus is part of the Simbu serogroup of the Bunyaviridae family, genus Orthobunyavirus.
Observational studies revealed that the virus is transmitted via insect vectors, mainly midges. The virus has been identified in pools of heads of Culicoides obsoletus and Culicoides dewulfi. Animal to animal transmission has been excluded at this stage.
A commercial ELISA kit for the detection of anti-Schmallenberg virus antibodies in ruminant serum and plasma is available.
UPDATE, 8 may 2012
Animal health: Schmallenberg virus isolated from ruminants in the European Union
Since November 2011, Schmallenberg virus has been reported in cattle, sheep and goats in eight EU Member States: Belgium, Germany, France, Italy, Luxemburg, the Netherlands, Spain, and the United Kingdom.
As midges are believed to be the major route of transmission, significant spread is unlikely during the winter period when these insects are usually inactive. Vector activity is expected to start again by the end of April.
Upon request of the European Commission, the European Food Safety Agency (EFSA) provided in February a preliminary analysis of the likely epidemiological scenarios that could be observed in animals in Europe. This analysis was based on the existing knowledge of viruses of the Simbu virus serogroup and other vector-borne epizootics (e.g. BTV8) in Europe. The hypothetical scenarios show that, depending on the temperature and the number of vectors, SBV might spread further in susceptible animal populations. Whenever the number of vectors per host and the temperature are above a specific threshold there is a possibility of further spread to additional Member States. In order to assess the extent of the outbreak in the EU, EFSA collected epidemiological data, at herd/flock level and animal level, from affected Member States. The collected data covered the period from 1 August 2011 to 16 April 2012, updating the previously published report on the epidemiological situation of SBV. Results of the analysis of the data collected were presented in two technical reports (‘Schmallenberg’ virus: analysis of the epidemiological data), published on 2 April and 4 May.
The total number of SBV confirmed herds in Europe as of 16 April 2012 is 3444. So far this year, no confirmed acute cases have been reported in adult animals. After a peak in week 9 (27 February– 4 March 2012), the number of reported SBV-confirmed herds decreased. This decrease is clearly observed in sheep, both in numbers of confirmed and suspected herds. However, no such clear decrease is observed in cattle. The decrease in number of confirmed herds is most probably linked to the end of the lambing season in affected countries. Maps representing the spatial distribution of cases are available in the reports.
Potential implications for human health
The results of the studies conducted by Robert Koch Institute (RKI) in Germany and National institute of public health and the environment (RIVM) in The Netherlands confirmed the preliminary assessment expressed by ECDC and the RIVM (see more information about the studies in the Joint ECDC/RIVM/RKI rapid risk assessment.)
ECDC fully supports the assessment results delivered by RIVM and RKI, which both conclude that the risk of infection of individuals exposed to SBV is absent or extremely low and that it is very unlikely that SBV poses a risk to humans.
These assessment results are based on the following observations:
- The genetically most closely related viruses (Shamonda, Aino, and Akabane viruses) have never been associated with disease in humans.
- People who have been in close contact with infected animals (e.g. animal workers, farmers, and veterinarians) have not reported any unusual disease.
- There is no evidence of any sero-conversion in people who presumably have been exposed to the virus.
In November 2011, public health authorities in the EU Member States were alerted about the outbreak of Schmallenberg virus (SBV) in ruminants. Since then, animal and human health authorities, both at national and EU level, have been closely collaborating on this topic to ensure the rapid detection of changes in the epidemiology in animals and humans, particularly among people who had been in close contact with infected animals.
Epidemiological and microbiological studies conducted by the Robert Koch Institute (RKI) in Germany and the National Institute of Public Health and the Environment (RIVM) in the Netherlands have confirmed that the zoonotic potential of SBV is absent or very low. ECDC fully supports the assessments results delivered by RIVM and RKI, which both conclude that it is very unlikely that SBV poses a risk to humans.
As a general precaution, animal workers, farmers and veterinarians are advised to follow existing protective hygiene measures when working with livestock and abortion material.