Scrapie Susceptibility codons 136, 154 and 171
Scrapie is an infectious disease; a susceptible animal must come in contact with the disease agent to become infected.
Sample Collection Instructions:
Ear Notch: A medium pig ear-notcher or ear-notching tool that yields a 1 cm notch works best if used on the lower aspect of the ear where the notch can be seen from a distance yet does not affect the function of the ear flap.
Clean the notching tool with disinfectant, then ALWAYS clean away any disinfectant with distilled water. It is important to remember that any residual disinfectant on the notching tool can cause false-negative results, therefore thorough rinsing with clean water is essential. Place the notch into a labeled, dry, red top collection tube with no formalin or other liquids. Collected ear notch MUST be free of contamination including dirt, feces, and tattoo ink.
Store collected ear notches for a maximum of 72 hours at refrigerator temperatures and ship over.
Prevention and Control:
Each gene has a pair of alleles, one on each chromosome of a chromosome pair. Alleles reside in the same site on each chromosome. When only codons 171 and 136 are considered and H or K at 171 is treated as a Q at 171, there are only four combinations that need to be considered in order to eliminate scrapie from a flock AARR, AAQR, AVQR, and QQ.
1. AA RR sheep are nearly completely resistance to scrapie. Only one case (in Japan) has ever been reported. These sheep are highly unlikely to carry or transmit scrapie;
2. AA QR sheep are rarely susceptible. In rare cases, AA QR sheep in Europe have become infected. Most but not all cases have been in flocks with high scrapie prevalence. It is unknown whether infected AA QR sheep can transmit the disease. The risk from exposed AA QR sheep is probably minor, since infected
AA QR sheep are rare and it is unusual for PrP scrapie to be found outside the brain of these sheep;
3. AV QR sheep are somewhat susceptible to some scrapie strains. Two cases have been identified in the US. The risk from exposed AV QR sheep is probably minor, since infected AV QR sheep are rare and it is unusual for PrP scrapie to be found outside the brain of these sheep. AV QR sheep are significantly less
susceptible to the scrapie strains that affect them than are the QQ sheep that are affected by these strains
4. QQ Sheep (AA QQ, AV QQ, and VV QQ) are susceptible to scrapie and can transmit the disease to susceptible flock mates.
Tools for Eradicating Scrapie
In addition to a genetics based flock clean up plan, USDA is using several tools to eradicate scrapie. These include (1) finding infected and source flocks through the testing of exposed animals traced out of known infected flocks and, beginning in April 2003, through slaughter surveillance, (2) identification of sheep and goats in commerce to allow for effective tracing of scrapie positive and exposed animals, (3) restricting the movement of genetically susceptible exposed animals, and (4) educating producers, veterinarians, and others about clinical signs of scrapie.