The Schmallenberg Virus (SBV) has been a recent hot topic for virologists, veterinarians and farmers alike, because it is a new virus that has spread rapidly across Europe and hurt the health and survival of cud-chewing farm animals, also known as ruminants. In the fall of 2011 scientists analyzed blood samples collected from dairy cattle on a farm near Schmallenberg, Germany who had been showing symptoms such as fever, diarrhea, reduced milk production and decreased appetite. Using a method called deep sequencing, the researchers were able to successfully identify the new virus gene sequence and subsequently named it after the town where the dairy farm and infected cattle were located. Since that time the SBV has been found on sheep, cattle and goat farms in more than 10 European countries ranging from those in the north such as Finland all the way to the west in Spain.
SBV belongs to a family of viruses called RNA viruses. The genetic material in these viruses is made from RNA instead of DNA. Like other related viruses, SBV is transmitted to an animal from the bite of an insect. Insects that transmit disease agents are known as vectors. Common insect vectors include mosquitos, ticks and midges. A recent study has suggested that European biting midges, which are tiny flies, are the likely vectors of SBV. Even though animals are infected with the virus from the bites of insects, there is no danger of humans becoming infected with the SBV when exposed to an infected animal.
In addition to the disease symptoms exhibited by adult animals, SBV can take a serious toll on unborn and newborn animals, when pregnant females are infected. The virus has been shown to cause significant birth defects in cattle, sheep and goats. These birth defects affect many parts of the animals’ bodies, including the limbs, spine and even the brain. In these cases, the animals are often too weak or sickly to survive. In addition, the virus causes stillbirths and abortions. These deaths have been observed most frequently in lambs, thus affecting European sheep farmers who rely on the animals for meat and wool production. Numerous recent news stories from the United Kingdom have reported on the significant losses of lambs, which have had a detrimental effect on farmers’ incomes. In one such news story a representative from a UK sheep farming industry group said that 20-50% of lambs were lost from 60 flocks. Losses to this extent cost farmers thousands of pounds. For instance, one farmer estimated that a loss of 324 sheep (300 of which were lambs) had cost him approximately £22,000 (or almost $35,000).
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Although a vaccine is not yet available to protect the animals against SBV, many virologists in Europe are ramping up their research efforts to better understand the virus to develop a vaccine a vaccine against it. PLOS Pathogens recently published a study a research group at the University of Glasgow in Scotland who successfully grew the virus in the laboratory. This provides important experimental tools to understand how SBV causes disease. Specifically, they manipulated molecules to create the virus from scratch in a form that can be easily introduced and replicated in cultured cells in the laboratory. In addition, the scientists were able to demonstrate how fast the virus grows in the brain and spinal cord of aborted lambs and calves. They showed that SBV prefers to infect nerve cells, also known as neurons, which explains why the virus damages the brain of infected animals. This also results in muscular defects such as abnormally flexed legs often seen in stillborn animals when virus is transmitted from an SBV-infected mother to the calves or lambs during pregnancy. This innovative research now makes it possible to manipulate the virus in order to develop and test novel vaccines against this newly emerged disease.
Varela M, Schnettler E, Caporale M, Murgia C, Barry G, et al. (2013) Schmallenberg Virus Pathogenesis, Tropism and Interaction with the Innate Immune System of the Host. PLoS Pathog 9(1): e1003133. doi:10.1371/journal.ppat.1003133
The Schmallenberg virus has created serious problems for farmers across Europe, whose lamb populations are significantly declining as a result. The need for an effective new vaccine against SBV is urgent, but now that the virus can be isolated, grown and studied in the laboratory, there is genuine hope that future research will lead to greater scientific understanding about the virus. This will, in turn, allow for the possibility to develop treatments to curb the spread of this new disease.
Gina Alvino, Ph.D. is a Senior Publications Assistant at PLOS Pathogens. She acknowledges PLOS Pathogens Editor in Chief, Kasturi Haldar and Deputy Editor, Grant McFadden for their editorial input on this post.