An Sci 362 1st Edition Lecture 25 Outline of Last Lecture I. Some definitionsII. What is bovine spongiform encephalopathy (BSE)?a. Causative Agentb. Symptomsc. TransmissionIII. BSE and vCJDIV. Genetic variation in the bovine prion proteinV. Testing for BSE and preventionOutline of Current Lecture I. What is scrapiea. Signsb. Diagnosisc. Causative AgentII. Genetic variation in the sheep prion protein and association with disease susceptibilityIII. Consequences of selectionCurrent LectureWhat is scrapie?- Progressive neural disordero Signs appear 2-5 years after infectiono Live 1-6 months after onset of clinical signs- Incidence of 0.2% (1 in 500) for mature sheep in USA- Costs American sheep producers $10-20 MD/yr in lost sales abroad, in increased costs, and in lost animals- Reported through the world (only Australia and New Zealand are free)- Not limited to, but most frequently observed in Suffolk breed in USA- Clinical signso Changes in behavior Hypersensitivity to noise or movement Scratching and rubbing  Diminished social interaction o Death, possibly suddenThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Neurological abnormalities  Loss of coordination Lip smacking Gait abnormalities, i.e. bunny hopping, walking on eggshellso Weakness, unable to riseo Weight loss- Could be confused with:o Ovine progressive pneumoniao Listeriosiso Rabieso External parasites (lice, mites)o Pregnancy toxemiao Toxins- Tests available for live animal and postmortemDiagnosis- Dead animalo Brain tissue and lymphoid tissue- Live animalo Lymphoid tissue of third eyelido Only effective 10-14mo post infection (low sensitivity)Causative Agent- Prion (abnormal form of a normal cellular protein)- Extremely resistant to heat- No detectable immune response or inflammatory reaction- In sheep, PRNP gene produces:- A normal cellular prion protein molecule PrPc- In infected sheep, PrPc is converted to: - PrPsc, scrapie prion protein molecule, the abnormal infectious form of the prion protein molecule - PrPc exists in all animals with small differences between species - PrPsc makes more of itself by causing misfolding of normal cellular prion protein. Transmission- Transmitted from affected ewe to susceptible offspring or other sheep by contact with placenta or placental fluids- In lab, transmitted by inoculation to - Hamsters, mice, rats, voles, gerbils, mink, - Cattle and some species of monkeys- No evidence for transmission to humans by contact with affected animals or carcasses from sameThe National Accelerated Scrapie Eradication Program- Individual ID requirement began September 2001o Applies to the following animals in commerce: Breeding sheep and most breeding goats of any age Most exhibition sheep and goats except wethers All sheep over 18 months of ageo Purpose: Able to trace scrapie infected and exposed animals Genetic Variation in Sheep PrP (prion protein)- In the PRNP gene, three codons affect scrapie susceptibility:o Codon 136: affects susceptibility in sheep exposed to some classical scrapie typeso Codon 154: minor role, not used in US regulatory programso Codon 171: major determinant of scrapie susceptibility - Codon 136 à valine (V) or alanine (A)- Codon 154 à arginine (R) or histidine (H)- Codon 171 à glutamine (Q), arginine (R), histidine (H) or lysine (K) - 2 x 2 x 4 = 16 possible haplotypes- Only 5-6 commonly seen- UK Haplotypeso A136R154R171resistanceo A136R154Q171susceptibility (esp. Suffolk)o V136R154Q171high susceptibilityo A136H154Q171resistance in some breeds ?o A136R154H171neutral ?- USDA -- ignore codon 154o Major forms A136R171(AR) A136Q171(AQ) V136Q171(VQ)o AQ and AR most common formso Minor forms A136H171 (AQ) A136K171(AQ)o Consider H or K at codon 171 equivalent to Q- USDA -- “There are only four combinations that need to be considered in order to eliminate scrapie from a flock”.o AARR (AR/AR) -- Nearly completely resistanto AAQR (AR/AQ) -- Rarely susceptible Some infected animals have occurred in flocks with high scrapie prevalenceo AVQR (AR/VQ) -- Somewhat susceptibleo QQ (AQ/AQ, AQ/VQ, VQ/VQ) -- SusceptibleGenotyping as a Tool in Preventing Scrapie- All QR placentas that have been examined from infected QQ ewes have been negative for scrapie whereas QQ placentas from infected QQ ewes have been positive.- Therefore, QR placenta/birth fluids from infected ewes are unlikely to transmit scrapie tonearby susceptible sheep.- Lambs have a combination of DNA from the ewe and from the ram:- a QQ ewe bred to an RR ram will produce a QR lamb with QR placenta/birth fluids. - A QQ ewe bred to a QQ ram will produce a QQ lamb with QQ placenta/birth fluidsAny Correlated or Pleiotropic Effects?- Pleiotropy -- Single gene has effects on more than one trait- Correlation -- Any closely linked genes with beneficial or detrimental effects on other traits of interest- Examined association of PRNP genotype with:o Lamb birth and weaning weights, single vs. multiple births, weight of lamb weaned per ewe- Multiple breeds evaluated:o Suffolk, Hampshire, Rambouillet, Columbia, Targhee and a commercial western white-face pop- Evaluated 25 growth, carcass and meat quality traits- Examined Dorset x Romanov F2 population- Limited effects observed (Romanov only):o ARR haplotype associated witho Longer carcasses P=0.013o Narrower rumps P=0.038o Less marbling