Bovine tuberculosis: increased surveillance in a worrying regional context

Bovine tuberculosis is classified as B in the Animal Health Act, a disease that must be eradicated in all European countries, and its management is overseen by the DDETSPP.

A contagious pathogen…

“The disease is caused by bacteria of the Mycobacterium genus (bovis, caprae, tuberculosis). They infect livestock, but also all mammals, including humans; it is a zoonosis.”

After contamination, the infection slowly develops with the appearance of caseous nodules. Symptoms are usually uncharacteristic early in the course, then weight loss and coughing dominate. The animal is contagious long before any clinical manifestation and even before the presence of visible lesions. Transmission occurs mainly through direct contact between an infected animal and a healthy animal.1 bacterium can be enough for the respiratory route!).

…and very resistant in the external environment

“Discard, urine and excrement being contaminants, the environment plays a big role in the persistence of the disease, the bacteria resisting for several weeks in the water or manure”

In contaminated areas, the risk factors identified are proximity to pastures, access to water points or ingestion of contaminated food (stem grass, salt rock, feeder).

Systematic prophylaxis in some departments…

To date, the Creuse is tuberculosis free and has no cattle for tuberculosis prophylaxis. In the affected areas, prophylaxis concerns all cattle over 24 months of age, which may be reduced to 18 months or even 12 months depending on the level of risk identified. Intradermotuberculination is comparative (IDC) to rule out reactions that would be due to other mycobacteria (avian or paratuberculosis, for example). The vet cuts the skin at two points on the neck, measures the thickness of the skinfolds with a cutimeter, injects avian and bovine tuberculins and remeasures the same skinfolds 72 hours later (+/- 4 hours) if the slightest thickening of the skin is detected to palpation. The result is considered negative, doubtful or positive comparing the thickening with the reference values. During any screening, it is the responsibility of the breeder to ensure that the animal is properly contained, with adequate facilities and human resources, on the day of the intradermal tuberculin test and during the verification, so that the veterinarian can carry out the injection and measurements in good conditions.

…and a worrying regional situation

25% of French farms were contaminated around 1950, but prophylaxis lowered this rate to 0.016% in 2005. Today, the annual incidence rate remains below 0.1% of herds, the threshold to maintain officially disease-free status. France, but tuberculosis outbreaks reappeared, especially in New Aquitaine. In 2021, 99 hotspots were declared nationally, including 70 in New Aquitaine (71%). This value remains globally stable despite the measures implemented.

New Aquitaine concentrates 71% of French bovine tuberculosis outbreaks.

A complex and long fight

“When an outbreak is confirmed, total culling is the rule to limit contamination of the environment, followed by extensive disinfection measures and a tracking space.”

The breeder is compensated and can then rebuild his herd. But in the historically most affected areas, environmental contamination makes combat complex. At farm level, prevention involves the implementation of biosecurity measures: isolation of animals introduced until the result of the control, footbaths for everyone involved, disinfection of shared buildings and equipment, management of effluents (especially manure), installation of double fences , placement of drinkers, feeders and salt rocks more than 80 cm from the ground.

Good cattle restraint for reliable intradermotuberculination

Animal restraint is an essential condition to be put in place by the breeder on the day of the intervention. AND during verification. The veterinarian performs the intradermal tuberculin skin test in several stages: mowing the injection area; measurement of the skinfold with the cutimeter; tuberculin injection into the dermis; After 72 hours, palpate the area with a new cutimeter measurement if the slightest thickening is observed.

In unharmed areas, movement monitoring…

In an uncontaminated area, the introduction of a carrier bovine remains the main factor of contamination. Initial herd status is verified by the GDS during any introduction to herd. If classified as “at risk of tuberculosis” (neighbor or former home), screening by the IDC had to be done before the cattle left. In addition, when an outbreak is discovered, an investigation is carried out by DDETSPP to identify herds with an epidemiological link. IDC screening can then be implemented on the herd (upstream link) or on produced cattle (downstream link). In Creuse, it was possible to identify a carrier animal in a derogatory fattening workshop, from an outbreak, leading to the slaughter of the animals and the disinfection of the place.

at the slaughterhouse, by examination of the lymph nodes…

Tuberculosis surveillance is carried out at the slaughterhouse by systematically examining the lymph nodes of the throat and lungs in cattle. Any evocative lesion is suspected, confirmed or invalidated by further analysis. In Creuse, in 2022, 11 suspected bovine tuberculosis originated from detection in the slaughterhouse, none were confirmed after analyzing the lesions. During the investigation period, farms are placed under APMS and may, under certain conditions, benefit from compensation under the FMSE.

…and wildlife

In areas where tuberculosis is established, wildlife is contaminated by contact with livestock and the environment, which can constitute a reservoir of the bacteria. Deer and badgers can then recontaminate livestock, with the case of wild boar and foxes remaining unresolved. In Creuse, wildlife monitoring is carried out within the Sylvatub network, complemented by departmental surveillance organized by the Fédération des Chasseurs de la Creuse, DDETSPP, DDT, LDA and GDS Creuse (cf. article of 06/01/2022). The checks carried out in 2022 were once again negative.

continuous surveillance

In the current regional context, surveillance must be required, both for breeders (knowledge of the situation of the herd of origin, isolating any introduced animal, having perfect containment for the eventual intervention of the veterinarian) and for veterinarians (performing IDCs with the maximum of rigor) or commercial operators. Biosecurity measures that are still insufficiently applied need to be developed. It is part of the GDS awareness and training axes in relation to veterinarians for breeders. Your health veterinarian, the DDETSPP and the GDS remain at your disposal for any further information.

DMV Jean-Yves POIRRIER – DMV Marie-Luc JEANDAUX – DDETSPP and DMV Boris BOUBET – Christophe LE MAUX – GDS Creuse – www.gdscreuse.fr

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