In November 2011, the Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health (FLI) first detected a virus of the genus Orthobunyavirus in cattle in Germany. Comparative analyses of the genetic material led to the assumption that the virus belongs to the Simbu serogroup (like e.g. Sathuperi, Shamonda, Aino, and Akabane viruses). The virus could be isolated, cultivated and replicated. Based on the geographic origin of the sample, the virus was named ‛Schmallenberg virus’ (SBV). Further investigations showed that it belongs to the species Sathuperi virus and is no reassortant (a new virus that has developed by exchange of genetic material from two or more viruses). The origin of Schmallenberg virus is still unknown.
The FLI developed a detection method (real-time RT-PCR) that has been made available to institutions in Belgium, France, England, the Netherlands, Italy, and Switzerland. Meanwhile, a test system for antibody detection is also available. Different research groups have developed prototypes for inactivated vaccines, none of which has however been granted marketing authorization yet.
Simbu viruses are widely distributed in Australia, Asia, and Africa and, as a rule, initially cause very mild clinical symptoms which can lead to a loss in milk production, fever etc that may persist for a few days. If pregnant animals are infected, however, temporarily delayed, sometimes considerable congenital damages, premature births and reproductive disorders may occur. The malformations are a long-term consequence of infection at an early stage of pregnancy. The virus is detectable in the blood of infected adult animals for a relatively short period of time only. Once infected, the animals develop immunoprotection which prevents repeated infection based on the current state of knowledge. So far, it is unknown how long this immunoprotection lasts.
According to the current state of knowledge, infection with SBV is more efficient in sheep than in cattle. In sheep, Schmallenberg virus so far has mainly been detected in the brain of malformed lambs.
Simbu viruses are mainly transmitted by biting midges. Biting midges infected with Schmallenberg virus have so far been detected in Belgium, Denmark, Germany, Italy, and Norway.
These viruses which are relevant in cattle do not represent a risk for humans. They are no zoonotic agents. Due to the relationship of ‛Schmallenberg virus’ with Sathuperi, Shamonda, Aino, and Akabane virus, a risk for humans is not to be expected (also see risk assessment of the European Center for Disease Prevention and Control). A study of the Robert Koch-Institute showed no evidence for infections of people with close contact to infected animals, especially sheep (also see information of the Robert Koch-Institute).