Medical Microbiology

474 8 VirusesasHumanPathogen

Allofthesediseasesaredesignatedastransmissibleencephalopathieschar-

acterizedbyincubationperiodsofanumberofyears,longdurationsofdis-

ease(onetoseveralyearsinhumans)andlethalcourseswithmotordistur-

bances(animals)andprogressivedementia(humans).Histologically,the

brainshowsnoinflammation,butrathervacuolizationofneurons,lossof

neurons,proliferationofglialcells,andamyloidplaques(seeabove).

Diagnosis.Thediagnosticprocedureishistological.Sincethereisnoimmune

responsetothepathologicalPrP,serodiagnosticmethodsareuseless.The

pathologicalproteincan,however,bedetectedinlymphoidtissuebiopsies

usingmonoclonalantibodies.

Epidemiology.CJD,whichoccurssporadically(onecasepermillioninhabi-

tantsperyear)isproducedanewineverycasebymutationsinPrPc.The

diseasecanbetransmittediatrogenically(brainelectrodes,cornealtrans-

plants).ThepathogenicityoftheGSSprion(PrPgss)isbasedonasingleamino

acidchange.Geneticfactorsalsoappeartohaveapredisposingeffectinview

oftheexistenceoffamilialformsofGSS.Kuruisadiseasethatwasspreadin

NewGuineabycannibalisticrites,probablyoriginatingwithacaseofCJD.

Kurunolongeroccurstoday.

Alimentarytransmissionispossibleinanimals.PrPscwastransmittedto

cattlebyfeedingthemanimalmealmadefromscrapie-infectedsheepre-

mains,resultinginBSE.Despitethefactthattransmissionofprionsfrom

onespeciestoanotherisnotasimpleprocessinprinciple,BSEprions

weretransmittedtohumansbythealimentaryroute,resultinginnvCJD.

ThisrouteoftransmissionwasconfirmedbystructuralanalyzeoftheBSE

andnvCJDprions.

From 1 995,whenthefirstnvCJDpatientdied,totheendof 200 0, 51 cases

ofCJDwithlethaloutcomehavebeendescribed.IncontrasttoclassicCJD,

theseinfectionsoccurredinyoungpeople,wherebytheincidenceofnvCJD

inolderpersonscanbemaskedbydementiasfromothercauses.Theex-

pectedoutbreakofnvCJDbecauseoftheBSEepidemiciscurrentlyatopic

ofextensivediscussion.

Asaresultofthisnewdiseasethreat,somecountrieshavenowprohibited

thefeedingofanimalmealtocertainkindsoflivestock(inparticularrumi-

nants).

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Kayser, Medical Microbiology © 2005 Thieme