Five questions on bluetongue

Bluetongue is a viral disease mostly affecting sheep, although it can also infect cattle, goats and wild ruminants. The virus responsible for bluetongue is an Orbivirus belonging to the family Sedoreoviridae. It has 36 different types, known as serotypes, and its pathogenicity varies considerably from one strain to another. The disease is an arbovirus: serotypes 1 to 24 of the virus are transmitted from one infected animal to another by the bite of a midge of the genus Culicoides. 

This strictly animal disease does not affect humans and has no impact on the quality of food from sick animals (meat, milk, etc.). The symptoms are fever, respiratory disorders, drooling, facial swelling and cyanosis of the tongue. Infected animals may also be asymptomatic. Some viral strains cause stunted growth in sick animals, death in some animals and abortions in infected females, resulting in significant economic losses for livestock farmers. 

Reported for the first time in South Africa, bluetongue has gradually spread northwards over the past few decades, probably due to global warming and international trade. Indeed, the transmission and geographical spread of this disease go hand in hand with the presence of populations of biting midges of the genus 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. In 2017, a serotype 4 virus was detected by the National Reference Laboratory for bluetongue, run by ANSES. This serotype then spread throughout mainland France.

A new type, serotype 3, arrived in Europe in late 2023. It mainly affects sheep, among which it causes high mortality. This new serotype was detected in France in early August 2024 and is also present in the Netherlands, Germany, Belgium and Luxembourg.

The most effective control measure known to date is vaccination. Measures can also be put in place to slow the spread of the virus when outbreaks are detected. They involve restricting the movement of animals susceptible to bluetongue within a 150 km zone around the outbreak: animals must have received an insecticide treatment two weeks prior to their departure and be negative for the disease before they can be transported anywhere else in France.

These measures, together with the vaccination campaigns on the French mainland between 2008 and 2010 with inactivated viruses directed against serotypes 1 and 8, have slowed the disease in France. However, from 2015, due to a lack of sufficient quantities of inactivated vaccines, vaccination was unable to control the re-emergence of two serotypes (BTV-8 in 2015 and BTV-4 in 2017). In August 2024, a campaign to vaccinate French livestock against serotype 3 was launched in response to detection of the virus in neighbouring countries and then in northern France.

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 studies to meet needs in terms of diagnosis, epidemiological surveillance and vaccinology.

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 sent to the veterinary laboratories. ANSES's NRL for bluetongue also takes part in the network led by the EU Reference Laboratory for bluetongue hosted in Algete, Spain.

Lastly, 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 or emerging threats. 

Research on bluetongue 

For several years, ANSES's Laboratory for Animal Health has been carrying out various research projects on bluetongue. These mainly aim to:

• characterise the bluetongue strains found in France at the molecular level;
• improve surveillance of bluetongue and epizootic haemorrhagic disease (EHD), which is caused by a virus closely related to that of bluetongue;
• produce proteins used to specifically detect serotypes 4, 8 and 3 of the bluetongue virus in ELISA tests;
• determine the presence of the bluetongue and EHD viruses in the French overseas territories and characterise the strains isolated;
• develop high-throughput rtRT-PCR tests for detection and typing of the bluetongue virus;
• study the virus's interactions with the cells of infected animals.

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 have also been made.

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. The bluetongue vaccines currently possessing MAs 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. In July 2024, after the contamination of farms by serotype 3 in Belgium and Germany, the ANMV issued temporary authorisations for use (ATU) for vaccines to counter this serotype.