Updated on August 17th, 2012
The emergence of a new previously unknown virus has created an international sanitary alert, especially in the European context. This virus, called "virus Schmallenberg", classified as a negative single-stranded RNA virus, belongs to the family Bunyaviridae and is responsible for causing primarily a reproductive disease in ruminants in northern Europe.
In the first epidemic wave (from December 2011 to May 2012) SBV affected eight countries of the European Union. On March 12th, 2012, Spain notified the first outbreak of Schmallenberg disease in a sheep farm in Córdoba (Andalusia). Up to date, infection has been confirmed in more than 4,600 ruminants, with a morbidity rate less than 2%.
The second epidemic wave has become evident in the last months, since several countries are notifying the birth of the typical malformed fetuses (see below) and the mild disease in adult cows. This suggests that SBV has the ability of overwintering in the affected countries. In addition, the virus was found in animals in Switzerland and Denmark.
Clinical findings are characterized by the appearance of fetuses with congenital malformations such as arthrogryposis, torticollis or brain hypoplasia, passing virtually unnoticed in adults. Transmission, like many bunyaviruses, is carried out by midges of the genus Culicoides, the same vectors that transmit the famous bluetongue virus. In fact, the region where outbreaks have originated and their geographical extent resemble the outbreaks of bluetongue serotype 8, occurred in the same countries since August 2006. However, the speed and spread area of SBV infection are much higher, suggesting that there may be several ways of transmission other than Culicoides spp.
Multiple antibody-based diagnostic techniques are designed. In fact, a vaccine against the virus is being developed, since infected animals show significant rates of neutralizing antibodies, encouraging data for the control of infection. Through metagenomics, a newly introduced diagnostic technique, the sequence of viral isolates has been identified. This pathogen is related to with other Orthobunyavirus members of the Simbu serogroup circulating in Asia, Oceania, America and Africa.
Although further epidemiological investigations are needed, this virus may alledgely be a variant of any of these Orthobunyavirus circulating in Africa, though recent studies point that SBV may be more ancient than expected. How it entered northern Europe is unknown. In fact, there are many uncertainties about the extent of this infection: how many animals will be affected, how long cases will continue to appear and how far the infection will spread. The long clinical silence (since an infected midge bites a pregnant female and the moment of parturition when congenital malformations are observed) hampers the notification of new cases of infection.
Therefore, and due to the first outbreak reported in Cordoba, Spanish Ministry of Agriculture, Food and Environment (MAGRAMA) will promote surveillance and control measures to address the potential infection.
However, given the low number of affected animals despite the rapid spread through Europe, health authorities of the European Union together with the OIE have decided not to include this disease in the list of notifiable diseases. This does not mean that the affected countries stop considering surveillance and control measures, since information about this new disease may serve to address the potential infection.
“Notes on Schmallenberg disease” (Spanish text)