Appeared in the XVIIIe century, scrapie has survived the decades without weakening. This disease deadly which affects sheep and goats is all the more formidable as no treatment manages to eliminate it. Point.
Sheep scrapie: what is it?
Sheep scrapie has been known for 1732, the year it was first observed in small ruminants (goats and sheep) in Britain. This fatal disease belongs to the group of subacute transmissible spongiform encephalopathies (TSSS). Decryption:
- Theencephalopathy is a disease characterized by degeneration of the brain;
- Spongiform means that the brains of animals become flabby and have numerous microscopic holes resembling the appearance of a sponge;
- Subacute indicates that after the onset of symptoms, the patient’s condition worsens irreparably until the subjects die in a few weeks or even a few months;
- Transmissible because the infection is due to the transmission of a pathogen (the prion).
Scrapie in sheep: the causes
If the precise origin of scrapie is not yet unanimous, the theory most recognized by scientists is the infectious agent named prion. This abnormal protein is resistant to enzymes and therefore does not undergo degradation. It is the accumulation of this defective, undegraded protein that causes the destruction nerve cells and spongiosis lesions seen in the brain.
Scrapie in sheep: modes of transmission
Scrapie infection in animals occurs by:
- Transmission horizontal, from mother to offspring through the placenta, the fluid or tissues of which may contain large amounts of pathogenic prions;
- Transmission vertical during ingestion of materials contaminated by congeners. Unharmed animals are thus infected when they consume or lick the placenta and the excrements present in the places of birth. The little ones get contaminated through breast milk.
You must know that :
- The males can contract scrapie but cannot pass it on to others;
- The Genoa of a sheep affect its resistance to disease and the duration of incubation;
- No demonstration of transmission toman has been established, but as a precaution, all affected animals are kept out of the food chain.
- A nervousness, teeth grinding, lip smacking, aggressiveness;
- A reflex of biting legs or sides;
- A licking and excessive scratching due to itching with pruritus;
- A fall from the oldest boy ;
- A weight loss despite a conservation of appetite;
- A state of weakness general (the animal remains lying down and is unable to get up);
- The dead : the affected animal can simply be found lifeless.
Scrapie in sheep: clinical signs
Scrapie is a slowly developing disease: the duration ofincubation ranges from a few months in very sensitive animals to several years (two years on average). However, in some cases the infection took up to eight years to manifest. Most detections occurred late (at the slaughterhouse or rendering plant) and very rarely by observation of clinical signs. The infection usually affects individuals aged 2 to 5 years, but the youngest subject identified had 7 months. Death occurs within two months of the onset of symptoms which are in particular:
- Troubles locomotors : tremors, lack of coordination, disorderly movements of the hind limbs causing “rabbit hopping”;
Scrapie in sheep: diagnosis
The diagnosis aimed at establishing with certainty the presence of the pathogenic prion responsible for scrapie is carried out on an animal dead. A microscopic examination of the brain tissue reveals spongiform lesions characteristics of the brain. Can also be analyzed: tonsils, lymph nodes or spleen after injection of a dye special. On an animal living, peripheral lymphoid tissue biopsy can accurately detect animals with scrapie. However, results negative do not mean that the subject is healthy, hence the impossibility of a definite diagnosis on living animals.
Scrapie in sheep: treatment and prevention
At present, there is no no treatment no vaccine against scrapie in sheep. In the presence of clinical signs, it is recommended toisolate the animal and burn the placenta and litter soiled with fluids and fetal membranes. It is also asked not to do breast-feed the young by suspicious mothers. In France, the state has set up prevention programs including:
- The genetic selection consisting in keeping the resistant animals, eliminating the most sensitive and repopulating the affected farms with resistant animals;
- Monitoring by survey on a sample of animals over 18 months old in slaughterhouses and rendering plants;
- The establishment of a monitoring network scrapie clinic in sheep and goats over 1 year of age with nervous disorders detected by health veterinarians;
- The intervention of a health police based on APMS surveillance (prefectural surveillance order) of the farm when scrapie is suspected.