With state-of-the-art techniques Central Veterinary Institute (CVI), part of Wageningen UR, has developed a new generation vaccine against Bluetongue serotype 8. This is not only a very safe vaccine but it also provides protection for animals three weeks after one low dose. Application for other serotypes of Bluetongue virus (BTV) is expected.
In Augustus 2006 Bluetongue serotype 8 was reported in sheep and later in cattle in North-West Europe, a serotype that was not circulating in Europe so far. It started a huge outbreak in Europe which was the largest outbreak of Bluetongue ever recorded. All ruminants are susceptible to Bluetongue via biting midges that have ingested the virus via a bloodmeal from an infected animal. Especially sheep show clinical signs after infection. Besides distress to animals and losses for the individual animal owner, the Bluetongue outbreak caused large economic losses due to the export ban for ruminants from affected countries.
Several seroptypes circulate not only in South Europe and Africa, but also in other parts of the world. It is not unlikely that North European countries will face future Bluetongue outbreaks because of international transport of animals, animal products and plants or via tourists who unknowingly take midges with virus into the country.
Via midges more vector-borne diseases
Culicoides biting midges currently living in North-West Europe can transmit viruses as has become evident with the outbreaks over Bluetongue and Schmallenberg. In addition, climate change would bring more exotic midges species to northern European countries that can spread vector borne disease, such as Bluetongue. Generally, there is no treatment for infected animals and prevention of infection by vaccination is the best way to combat vector-borne diseases. The currently available vaccines, live-attenuated and inactivated vaccines, all have one or more disadvantages, and are only marketed for a limited number of serotypes. The international call for new and improved vaccines for more serotypes is obvious.
Since a protein involved in virus release is missing, vaccine virus hardly enters the bloodstream, and is not released from insect cells. It only multiplies minimally in the vaccinated animal. Thus, midges can neither pick up the vaccine virus nor can spread it to other animals, and is therefore named DISA vaccine. The DISA principle is an acronym for Disabled Infectious Single Animal.
This DISA vaccine developed by the Virology department of CVI contains all the achieved qualities of the currently available vaccines without the remaining disadvantages of these vaccines. The vaccine is based on live-attenuated BT vaccine for serotye 6, that is adapted for serotype 8 and is missing the protein important for virus release. Application for other serotypes is also achievable.
The missing protein further weakens the vaccine virus, makes it safe, and induces a quick and full protection against Bluetongue virus serotype 8. Since the missing protein is not made at all, the vaccinated animal does not raise antibodies against this specific virus protein, which opens the possibility to differentiate infected from vaccinated animals, the DIVA principle. This is vital information for the control of animal diseases.
The missing protein in DISA vaccine leads to avirulence, strongly reduced viraemia, and therefore does not cause any clinical signs but does fully protect ruminants. In addition, by lack of viremia vaccine virus cannot be picked up and spread by midges. This prevents spread of vaccine virus to other animals and a possible return of virulence by mutations. The most important fact of this finding is the coupling of all desired vaccine properties regarding safety – i.e. nonvirulence, DISA and DIVA principle – by one change (deletion) in the bluetongue virus.