European Reference Laboratory confirms bluetongue virus serotype 3

The serotyping at WBVR was performed using Whole Genome Sequencing. “Thanks to this new technique, we know the serotype we are dealing with much earlier compared to previous bluetongue outbreaks,” says Piet van Rijn, senior researcher at WBVR and specialised in bluetongue.

Serotype 3 has been reported in southern Italy, Sicily and Sardinia. In terms of pathogenicity and level of spread this serotype appears to be similar to what has been observed in 2006/2007 in with serotype 8. "I fear that we can still expect many infections in the coming period,” according to Van Rijn during the Bluetongue webinar (in Dutch) that was held on September 8. The webinar was a joint initiative of the Animal Health Service (Royal GD), WBVR and trade magazine Het Schaap.

Serotype origin

Serotype 3 is the most recently reported serotype in Europe, presumably the virus entered from Tunisia to Italy. The bluetongue virus has more than thirty different serotypes that raise little or no cross-protection. Within the many serotypes, serotype 3 forms a kinship cluster with serotypes 13 and 16 (see figure 1). According to Van Rijn, the origin of a specific serotype of the bluetongue virus is difficult to trace. "In 2006, we were confronted with serotype 8 in Northwest Europe, a type that did not occur in Europe until then. To this day, it isn’t clear where the serotype came from."

Transfer

It is clear that bluetongue is transmitted by midges, a small fly with a few millimeters in size. Compared to the mosquitoes that people know, a much smaller insect that is not directly observed with the naked eye. “But they are very numerous,” says Van Rijn. In the midges, the virus can multiply, after which it is released through the salivary glands to the susceptible host (ruminants) at the time the midge takes a blood meal. Once in the ruminant, the virus can multiply, which eventually leads to the clinical symptoms known from bluetongue (including lesions on the tongue, point bleeding, nasal discharge, edema, etc.). All ruminants are susceptible to the bluetongue virus. Veterinarians note that the clinical signs in sheep are currently more severe than in cattle and goats.

Treatment

During the previous outbreak of bluetongue serotype 8, a vaccine was developed that proved effective against the disease. To Van Rijn’s knowledge, a vaccine has not yet been developed for serotype 3. “For sure not a vaccine based on dead virus like we use in Northwest Europe.” Van Rijn calls upon pharmaceutical companiesto take up the development of a vaccine quickly. “The chances of this virus dying out due to a harsh winter are slim. The sooner we have access to a working vaccine, the faster we can stop the disease,” emphasises Van Rijn.