2024-09-02 11:48:11
This article is reproduced from dialogue sous licensed under Creative Commons. liraOriginal article.
*Conversation: What are the symptoms of bluetongue? *
Stephen Zientala : Bluetongue (BCF) is a non-communicable disease that infects a large number of domestic and wild ruminants and produces a variety of clinical symptoms. Fever, depression, dyspnea, and anorexia are typical symptoms in affected animals. Tongue cyanosis sometimes occurs: an abnormal blue or gray discoloration of the skin due to insufficient oxygenation of the blood, hence the name “blue tongue.” In the most severe cases, FCO can cause hemorrhagic fever and death in animals, especially sheep, the most susceptible species.
Goats and cattle usually show few or no signs of the disease. However, long-term viremia (levels of viral particles in the blood) has been observed in cattle, traditionally thought to be the source of infection. FCO has been included on the list of notifiable diseases to the World Organization for Animal Health (WHOA) since the 1960s due to its economic and health impacts on affected livestock.
TC: What causes this disease? How is it spread?
Shenzhen : The causative agent of FCO is bluetongue virus (BTV), which belongs to the genus BTV Circovirus within the family Astroviridae. Like other members of this family, BTV is a non-enveloped virus. Its genome consists of 10 double-stranded (ds) RNA segments that can be reassembled like influenza or other segmented viruses.
It encodes seven structural proteins (VP1 to VP7) and five nonstructural proteins (NS1 to NS5). VP2 forms the outer capsid of the virus and is considered the major serotype-defining protein of the virus. A serotype is defined as all the characteristics of certain viruses that make it possible to distinguish strains belonging to the same species.
As of 2008, there were 24 serotypes of the virus, but more serotypes have been discovered in recent years. A total of 36 BTV serotypes have been described, and other serotypes have recently been identified, particularly in countries bordering the Mediterranean basin.
BTV is an arbovirus spread through the bite of female midges of the genus Culicoides when they feed on the blood of infected animals. Serotypes 1 to 24 are mainly transmitted by midges, while others are transmitted by direct contact.
**TC: Are there risks to human health from the virus itself or from eating contaminated meat?
Shenzhen : The virus can infect many animal species but causes clinical signs, particularly in sheep (hence the name bluetongue), but also in cattle.
This virus cannot be transmitted to humans. Furthermore, it is safe for us to consume products (meat, milk, etc.) from infected animals.
**TC: What is the health situation like in France? What are the dynamics of animal epidemics?
Shenzhen : Before 1998, there were no FCOs in Europe. From 1998 to 2006, a few serotypes emerged in the Mediterranean basin, but it was only from 2006 that FCO became a real concern in the animal health field. In August 2006, the first epizootic outbreak associated with an unknown strain of BTV-8 was detected in the Netherlands, which had never reached this latitude. In late 2006, the virus spread rapidly to Belgium, Germany, Luxembourg, and northern France. It spread to the United Kingdom, Denmark, Switzerland and the Czech Republic, affecting nearly 60,000 mining operations.
At the same time, the BTV-1 strain that emerged in North Africa in 2006 spread on the one hand in Sardinia and on the other hand crossed the Iberian Peninsula to southwestern France in the summer of 2007. The spread continues, with France being the worst-affected country, with more than 24,000 cases of BTV-8 and more than 6,000 farms infected with BTV-1.
In 2008, large-scale vaccination campaigns with inactivated vaccines were launched across Europe, which significantly reduced the number of epidemics and thus curbed the spread of the epidemic. However, it was not until the second mass vaccination campaign the following year that the number of BTV-8 cases in France decreased significantly (an outbreak of 83 cases at the end of 2009). Most European countries returned to BTV-8 free status between 2010 and 2012. get hurt.
Three years after the elimination of BTV-8 in France, in September 2015, this serotype was detected again in a ram in the Allier department that developed clinical signs suggestive of FCO (increased body temperature, respiratory problems and facial edema). Despite control measures taken by health authorities, BTV-8 spread rapidly throughout much of France over the next few years (more than 3,000 cases). In April 2019, the virus spread to Germany, Switzerland and Belgium. From a pathophysiological point of view, almost no clinical symptoms were observed in the BTV-8 outbreak in France between 2006 and 2008.
In November 2017, serotype 4 virus was introduced from Corsica. Since then, two more endemic animal infections of serotypes 4 and 8 have appeared in France.
In 2023, a serotype 3 virus (BTV-3) was discovered in the Netherlands. The virus killed more than 55,000 sheep. It spread to Germany, Belgium and England. In 2024, the virus crossed the French and Belgian borders. As of August 28, there were more than 190 households in the northern French provinces.
**TC: How to fight FCO?
Shenzhen : There is no antiviral treatment (drug). Vaccination helps prevent infection and reduce viral circulation. Inactivated vaccines against serotypes 3, 4, and 8 are available.
In 2008, large-scale mandatory inactivated vaccination campaigns for cattle and sheep were carried out across Europe, which greatly reduced the occurrence of the epidemic and thus curbed its spread. However, it was not until the second mass vaccination campaign the following year that BTV-8 cases in France decreased significantly. In France, the use of inactivated vaccines against BTV-1 and -8 made the elimination of BTV possible in 2010, and the country was deemed free in December 2012.
However, the high cost of mass vaccination limits the implementation of this vaccine.
Movement restrictions and vaccination measures aim to reduce the clinical consequences of infection and reduce the spread of the virus. During the epidemic from 2006 to 2010, losses amounted to hundreds of millions of euros.
Nowadays, when an epidemic is detected, a 15-kilometer restricted zone is established. Animals can only leave the area after a PCR test (with a negative result). Implementation of vaccination will reduce the intensity or reduce clinical symptoms. When animals are exported, they are also treated individually with PCR control measures and pesticides. The aim of these measures is to reduce the impact of the disease on infected animals, limit the spread of the virus within the territory and prevent its spread to free areas/countries.
Comments collected by Benoît Tonson, Head of Science at La Dialogue France
Stéphan Zientara is a veterinarian and virologist. He works at ANSES on infectious, zoonotic and vector-borne diseases. He is the director of the Animal Health Laboratory.
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