Synonyms

Blue tongue disease

Name of the disease in English

Blue tongue

The disease in brief

General disease of domestic cattle, sheep, goats and many species of wild ruminants, not transmissible to humans, with no health impact on foodstuffs of animal origin, due to infection by an Orbivirus (Blue Tongue Virus or BTV), not contagious between animals, but transmitted by various insects (arbovirus), in particular midges (Culicoids spp).

If the infection is seasonal (beautiful season in particular autumn), because centered on the periods of activity of the vectors, the clinical expression can be observed over a much larger period (including winter, except period of exposure to the virus), due to the impact on gestation and the possible anatomical abnormalities induced in the fetus, and observed at birth (congenital malformations, in particular nervous).  

The disease is described in many countries of the 2 hemispheres. Currently, 27 different serotypes of BTV have been identified, each with a specific geographic distribution that changes over time. For example, serotypes 8, 1 and 4 were successively detected in mainland France between 1987 and 2020.

Transmission between farms and between countries is explained by the movements of animals infected by the virus and reservoirs of contamination for the vectors (trade in live animals), and by the movements of the vectors themselves, during exchanges animals or various goods, or under favorable climatic conditions (the wind is likely to carry vectors over very long distances).

The severity of clinical disorders at the individual level varies widely, from asymptomatic infections to direct mortality. The economic impact is also very variable at the breeding and country scales. This variability is explained by the viral serotype, the receptivity / sensitivity of the animal, in particular in relation to its species characteristics (sheep classically considered to be more sensitive than cattle), and specific immunity (individual and herd). , as well as by the abundance and spread of the vectors themselves.

Post-infectious immunity is classically considered to be serotype specific; however, heterologous protection is possible, more or less marked and variable depending on the serotypic “pairs” considered.

Clinic & diagnosis

The suspicion of FCO rests

• on the circumstances of appearance (good season with access to pasture and period of vector activity),
• on various symptoms combined with fever, or combined with each other,
• muzzle lesions, markedly congested, with possible erosions ("cooked", "burnt" muzzle), which extend to the border of the adjacent skin, and are a frequent warning sign, especially in breeds with depigmented muzzle,
• lesions of the mouth, with swollen and painful walls / lips, congestive mucosa with possible superficial ulcers (<1.5cm), in particular of the gums but possible also on the palate,
• lesions of the nasal openings, with possible erosions of the mucous membrane, and serous or mucopurulent discharge,
• lesions of the eyes, with inflammation of the conjunctiva, causing discharge that agglutinates the hairs (epiphora, chassie); the cattle "cry", the eyelids often half-closed,
• teat lesions, swollen and painful, with congested or hemorrhagic stinging skin (petechiae), or with ulcers / scabs, which may extend to adjacent skin, causing milking difficulties in dairy breeds , or stubborn in suckling breeds, but in the latter case often not detected by the breeder,
• lesions of the limbs, characterized by sloping edema (swollen fetlocks), congestion of the crown and interdigital space; the call sign is lameness, with difficulty in gait, with small steps, with a hunchbacked pace, as "on pins",
• reproductive disorders, which may result, at the herd level, by possible abortions at different stages of gestation, without clinical particularities, and by a deterioration in fertility indices, with in particular a decrease in the pregnancy rate at 90 days, an increase in the calving-calving interval, the empty cow rate, the stillbirth rate,
• anatomical abnormalities, in particular of the nervous system (hydranencephaly, etc.), detectable from birth (congenital) or delayed (a few weeks, months), and characterized, among other things, by behavioral disorders, state of vigilance (calf “Idiot”, “soft”, with difficulties of the head…).

 

 

Typical sign of the disease

No description

Pictures

See below

Diagnostic formulas

No description

Differential diagnosis

-Foot and mouth disease MC

-Acute mucous membrane disease DG44.5

- Gangrenous coryza

-IBR

-Papular stomatitis DG10

-Helitis ulcerative herpetic MA47

- Nickname cowpox

- Photosensitization

- Schmallenberg disease

- Abortions

- Congenital anatomical malformations

 

Confirm a suspicion?

During the acute phase of the disease, taking blood on an anticoagulant (Tube-EDTA-Purple stopper) allows the presence of the virus to be confirmed by a PCR test.

After the acute infection, a blood sample on a dry tube makes it possible to carry out a serological test to find traces of viral passage or of a vaccination! There is no reliable serological test to differentiate the antibodies produced after viral infection and the post-vaccine antibodies.

Prognosis and treatment

The vital prognosis is often not committed in cattle, and for most strains. The economic prognosis is reserved, in particular because of reproductive disorders, for certain serotypes, or for territories hitherto free.

No specific treatment, only symptomatic treatment, based on anti-inflammatory drugs and the prevention of possible bacterial complications (antiseptics - topical antibiotics), in particular when the teats are affected (complications of mastitis).

Prevention

The control and prevention of BCF are managed by the State - Ministry of Agriculture - Directorate General of Food (DGAl).

BLF is a notifiable disease to the World Organization for Animal Health (OIE).

Within the EU, the Animal Health Act (LSA), which entered into force on April 21, 2021, classifies BCF in the categories

• C (diseases subject to voluntary control by EU Member States - Voluntary but optional eradication),
• D (controls and restrictions on trade between Member States - certifications),
• E (monitoring and reporting).

The precise prevention or action measures change over time, depending on the goals (eradication, control) displayed (European Union and France, or third countries, etc.), and the epidemiological (serotype-s) and technico-economic context (export, production breeding, selection units,…).

In practice, prevention measures are divided into 3 main areas,

• the vaccination,
• monitoring and screening for viral infection,
• purely sanitary control of animal movements according to different perimeters (surveillance, prohibition), established at different territorial scales.

For an update of the data, consult in particular  

• the website of the DGAl - Ministry of Agriculture, official bulletin, technical instructions: https://info.agriculture.gouv.fr/gedei/site/bo-agri/supima/6e21dc0f-bd0c-42d6-9164-24e0728797e3#

the site of the animal epidemiological surveillance (ESA) platform: https://www.plateforme-esa.fr/page/thematique-fievre-catarrhale-ovine

References