In a matter of months, a new virus has succeeded in infecting a large majority of ruminants in Europe. While not particularly worrying in adult animals, the clinical signs in foetuses infected during gestation are, however, alarming: abortion, hydrocephalus, muscular atrophy. A team from the University of Liège’s Pathology Laboratory is closely monitoring this new epidemic.
In autumn 2011, breeders and vets in the eastern part of the Netherlands and the west of Germany discovered the first clinical signs of a new epizootic. The symptoms in their cows, sheep and goats were fever, diarrhoea and a drop in milk production. These symptoms very quickly affected a large number of animals on the same farm and as it was identified in numerous farms in a given geographic region, the situation began to resemble the start of a new epidemic. Hence, the next step was to find and understand the nature of the disease to be able to estimate the seriousness of the situation and get it under control as quickly as possible. While the clinical signs in adult ruminants aren’t alarming, those present in foetuses infected during gestation are significantly more striking. “The symptoms observed in adult animals aren’t very specific and only last about a week. On the other hand, this new pathogen can cause abortions and serious malformations, especially in the nervous system of young animals infected during gestation”, explains Mutien-Marie Garigliany, doctor in veterinary medicine and research assistant at ULg's Pathology Laboratory, led by Professor Daniel Desmecht.
A new hybrid virus
Researchers at the Friedrich Loeffler Institute (FLI), the main federal German research organisation for animal health, were therefore quick to begin looking for the causes of this epidemic. Since the traditional analyses didn’t provide any results, the scientists launched a metagenomic study. “This consists of randomly amplifying all the pieces of RNA and DNA contained in the samples taken from animals affected by the disease and then sequencing them all”, explains Mutien-Marie Garigliany. By amplifying all the genetic material in this way, the researchers came across many things of little interest, such as pieces of the genome of the sick animals or genetic material belonging to traditional pathogens found in ruminants. “But they also spotted an Orthobunyavirus-like viral genome similar to the Shamonda virus and they wondered whether this was the source of the problem”, the researcher from Liège points out. On the basis of the first sequences obtained, the FLI team created an initial PCR (polymerase chain reaction) and realised that all the samples from the animals showing clinical signs contained genetic material from this virus!
Once this initial observation had been established, the German scientists analysed the pieces of the viral genome more closely. It was then that they discovered that the pathogen in question wasn’t the Shamonda virus but a new one. “Like the flu virus, this new virus is composed of several genomic segments”, Mutien-Marie Garigliany emphasises. “The Schmallenberg virus, named after the German town where the first cases were discovered, contains three genomic segments, two of which come from the Shamonda virus and one from the Sathuperi virus”, he continues. Well known and identified quite some time ago already, first in Africa then in Asia, these two viruses are relatively inoffensive. “The specific combination of the genomic segments as found in the Schmallenberg virus cause a virulence that isn’t observed in the ‘parent’ viruses”, the researcher points out.