Updated on 05/01/2021
Bluetongue, Animal diseases, Animal health
Bluetongue is a viral disease of ruminants, and does not affect humans or food. It is transmitted by midges and can cause major economic losses in animal husbandry. Vaccination is the most effective means of prevention, but is expensive. Here is a profile of the disease and an overview of the work of ANSES, a leading player in the fight against this virus.
1/ What is bluetongue?
Bluetongue is a viral disease mostly affecting sheep, although it can also infect cattle, goats and other wild ruminants. The virus responsible for bluetongue is an Orbivirus of the family Reoviridae. There are 27 different types of this virus – called serotypes – and its pathogenicity varies considerably from one strain to another. It is an arbovirus, transmitted from one infected animal to another by the bite of a midge of the genus Culicoides.
Did you know?
Bluetongue is on the list of notifiable diseases of the Terrestrial Animal Health Code of the World Organisation for Animal Health (OIE) and as such, is subject to mandatory reporting to the OIE. Its appearance in a country results in severe commercial restrictions concerning all animals susceptible to the disease (mostly sheep, cattle and goats), as well as their semen, eggs and embryos.
2/ What are the symptoms of bluetongue?
This strictly animal disease does not affect humans and has no impact on the safety of food from sick animals (meat, milk, etc.). The symptoms are the same for serotypes 1, 8 and 4: fever, respiratory disorders, drooling, oedema of the face, cyanosis of the tongue. Infected animals may also be asymptomatic. Some serotypes cause growth retardation in sick animals, death in some animals and abortions in infected females, resulting in significant economic losses for livestock farmers.
3/ Where is bluetongue found?
Initially present in Africa, bluetongue has gradually spread northwards over the past few decades, probably due to global warming and international trade. Indeed, the transmission and geographical extension of this disease go hand in hand with the presence of populations of biting midges (Culicoides), which act as vectors and whose proliferation is favoured by high temperatures. The disease is now present on every continent except Antarctica.
In 2006, it arrived in Northern Europe – Germany, Belgium, the Netherlands – before spreading very rapidly to France. In the years before 2010, north-western Europe experienced several bluetongue epizootics caused by serotype 8 (or BTV-8) and serotype 1.
Following a mandatory vaccination campaign with inactivated vaccines against serotypes 1 and 8, France regained its disease-free status in 2012. In 2015, ANSES's Laboratory for Animal Health (the National Reference Laboratory) again detected a serotype 8 virus in central France, which then spread throughout the country. In 2017, the NRL detected a serotype 4 virus that also ended up infecting mainland France. In 2020, France was officially infected with both serotypes 4 and 8.
4/ What is being done to prevent and control bluetongue viruses?
The most effective control measure known to date is vaccination. Alongside the health measures put in place, vaccination campaigns on the French mainland with inactivated viruses directed against serotypes 1 and 8, from spring 2008 until autumn 2010, slowed the disease in France. However, from 2015 onwards, vaccination was unable to control the re-emergence of two serotypes (BTV-8 in 2015 and BTV-4 in 2017) due to a lack of sufficient quantities of inactivated vaccines.
5/ What is ANSES’s role in preventing the spread of bluetongue?
ANSES has been developing expertise in bluetongue since 2011. Drawing largely on the skills available, the dedicated facilities and the experience acquired, the Agency has carried out various work to meet needs in terms of diagnosis, epidemiological surveillance and vaccinology.
Current research on bluetongue
- Molecular characterisation of strains of bluetongue serotypes 4 and 8 isolated since their emergence;
- A new approach for monitoring bluetongue and epizootic haemorrhagic disease (EHD), another virus similar to bluetongue, in the Mediterranean basin;
- Production of recombinant proteins to assess their antigenic properties and their use as antigens for ELISA tests specific to serotypes 4 and 8 of the bluetongue virus;
- Survey in the French overseas regions to determine the presence of bluetongue and EHD viruses and characterisation of isolated strains;
- Development of high-throughput rtRT-PCR for detection and typing of both orbiviruses (bluetongue and EHD);
- Study of the pathogenesis of orbiviruses through the search for cellular partners;
- Role of the interferon pathway in host restriction mechanisms.
Assessing the risks associated with bluetongue
The Agency is regularly called upon by the Ministry of Agriculture to analyse the health situation, assess the risks associated with bluetongue, and propose and assess changes in surveillance and control measures, at national and sometimes local level. Its opinions have helped identify a number of areas where research is needed to improve risk assessment and more effectively control the spread of the virus. Several recommendations on surveillance, control and prevention measures have also been made. Following the outbreak of serotype BTV-1 in Corsica in early September 2013, an Emergency Collective Expert Appraisal Group (GECU) was set up to answer questions from the DGAL on the assessment of management measures for bluetongue outbreaks.
National Reference Laboratory (NRL) for bluetongue diagnosis
ANSES's Maisons-Alfort Laboratory for Animal Health performs virological diagnosis (detection of the viral genome by PCR, typing, viral isolation) as well as serological diagnosis.
As part of its reference activities, this laboratory develops PCR diagnostic techniques and coordinates the network of departmental veterinary laboratories for molecular diagnosis. The real-time PCR technique, developed in the NRL, has now been decentralised to 65 of these laboratories.
Together with three manufacturers, the NRL also took part in the development and validation of commercial kits for quantitative PCR (PCRq) to ensure rapid distribution of diagnostic kits to approved departmental laboratories. ANSES's NRL for bluetongue also participates in the network led by the EU Reference Laboratory for bluetongue hosted in Algete , Spain.
ANSES is actively involved in the National epidemiological surveillance platform for animal health, which ensures that the measures taken to monitor health hazards in France are adequate for dealing with current hazards or emerging threats.
Bluetongue vaccine assessment and authorisation
The French Agency for Veterinary Medicinal Products (ANMV) assesses national and European applications and, where appropriate, issues marketing authorisations (MAs) for all veterinary medicinal products.
Currently, the fourteen vaccines with MA are inactivated vaccines containing either a single serotype (serotypes 1 or 8) or two serotypes (serotypes 1-8 or 2-4). They are intended for use in cattle and/or sheep to prevent or reduce viraemia and, in some cases, to reduce the clinical signs caused by the bluetongue virus.
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