Schmallenberg virus (SBV) and vaccine
The schmallenberg virus (SBV) has only recently in 2011 appeared in Europe and affects ruminants – cattle, sheep, goat and bison. In adults, the infection is transient, lasting less than a week and largely asymptotic except in cattle where it causes fever, diarrhoea and a drop in the milk production. However, the virus can cross the placenta in pregnant animals, cause abortions or infect the developing foetuses, attack their nervous system and cause abnormalities and deformities.
A new virus for Europe
SBV is part of the Bunyaviriadae viruses, RNA viruses that replicate in the cytoplasm and mature and assemble intracellularly by budding at the Golgi membrane. It is also part of the Orthobunyavirus family and the Simbu subgroup, all of which are transmitted by mosquitoes and/or midges. Those viruses are mostly found in Asia, Africa and Australia.
The first instance of the virus in Europe was confirmed during the summer of 2011 in Germany, closely followed by the Netherlands. Confirmation of the causative agent by next generation sequencing and metagenome analysis came in November 2011 from the Freidrich-Loeffler-Institut, the main German government research Institute for the study of animal disease. In early 2012, France, then the UK, Italy and Luxemburg were affected, closely followed by Spain. The disease spreads fast, carried by biting midges (Culicoides), which are quite common in Northern Europe.
The Development for Environment, Food and Rural Affairs (Defra) and the Met Office modelling of wind patterns suggested that midges blowing across the Channel from the European mainland carried the virus into the UK. The disease might also have been introduced through the import of infected animals, or might have been present in the country for a longer period at a low and undetected level.
Today, the numbers of sheep and cows infected with SBV in the UK is higher than previously thought. Researchers at the Duchy College in Callington explained that vets had estimated that the virus was in nearly 60% of dairy herds and 42% of sheep, but a new survey suggests that the estimated figers are as high as 80% for dairy herds and 70% for sheep. (2)
Two vaccines against SBV
Before the occurrence of vaccines against SBV, the best measures the farmers had to avoid infection of their herd was prevention. Infected animals were isolated and measures were taken to avoid midges, specifically during breeding seasons. A specific PCR test could be used to detect the virus in deformed foetuses and suspecting animals. A serology test was also available to screen for antibodies to the virus in blood samples.
However, in 2013, a first vaccine against SBV became available. Bovilis SBV developed by the animal health company Merk MSD was “welcome news for British farmers,” says Alick Simmons, deputy chief veterinary officer at DEFRA. “The vaccine gives extra assurance against this disease on top of the natural immunity we expect sheep and cattle to develop after initial exposure.” (3)
In 2014, a second vaccine, SBVvox, manufactured by Merial Animal Health (MAH) scientists in France, gave farmers multiple choices to fight SBV. The company claims it is the only vaccine licenced for the prevention of the disease, by stopping the viruses from entering the blood stream of both cattle and sheep, rather than just reducing the viral load in the blood. “SBVvox will provide a cost-effective solution for producers who want to protect their flocks pre-tupping. We also believe that it will be a useful tool for beef or dairy farmers, bringing replacements into their herds and vaccinating prior to bulling.” Says Findlay MacBean, Merial’s head of large Animal Buisness.
Both vaccines were granted a provisional licence in order to get the product on the market without many years of lengthy testing. However, one of the limitations of a provisional licence is that the manufacturers do not yet know if the vaccine protects for life or needs the occasional booster.
“It is great to have two products on the market for sheep farmers who are worried about the risk of Schmallenberg infection to their flocks. NSA applauds the Veterinary Medicines Directorate (VMD) for granting provisional licences in the way it has, as the rapid emergence of Schmallenberg meant we could have gone for months , if not years, with no protection had we had to wait for full licences.” Says Phil Stocker, NSA Chief Executive.
Is there a risk for humans ?
There is currently no peer-reviewed scientific evidence that Schmallenberg infects people or other animals, besides ruminants, even in close contact with infected animals. As yet, no human cases of Schmallenberg virus have been detected in any country, and the most closely related viruses only cause animal disease. Early assessments of the virus suggest that it is unlikely that it can spread to humans.
However, this risk cannot be ruled out, pregnant women are advised to avoid close contact with animals that are giving birth, as there is a theoretical risk of infection from sheep, goats and cattle that could harm a woman’s own health and that of her unborn child.
The disease is unlikely to have an effect on human health but it has had a huge economic impact on the traffic of ruminants across Europe. Major trading partners such as Russia placed a ban on the import of animals from Europe.