Medical Microbiology

Nematoda(Roundworms) 597

Trichinella

Causativeagentoftrichinellosis

&HumanscanacquireaninfectionwithlarvaeofvariousTrichinellaspecies

byingestingrawmeat(frompigs,wildboars,horses,andotherspecies).

Adultstagesdevelopfromthelarvaeandinhabitthesmallintestine,where

thefemalesproducelarvaethatmigratethroughthelymphaticsandblood-

streamintoskeletalmusculature,penetrateintomusclecellsandencyst

(withtheexceptionofTrichinellapseudospiralisandsomeotherspecies

whichdoesnotencyst).Clinicalmanifestationsoftrichinellosisarecharac-

terizedbyintestinalandmuscularsymptoms.Diagnosisrequiresmuscle

biopsiesandserumantibodydetection. &

Parasitespeciesandoccurrence.EightTrichinellaspeciesandseveralstrains

havebeendescribedtodatebasedontypicalenzymepatterns,DNAse-

quences,andbiologicalcharacteristics.Theareasofdistributionarelisted

inTable 1 0. 5 ;severalTrichinellaspeciesoccursympatrically,i.e.,inthe

samegeographicregion(Table 1 0. 5 ).

ThemostwidespreadandmostimportantspeciesisTrichinellaspiralis,

whichdevelopsmainlyinasynanthropiccycle.Despitethegenerallylow

prevalenceofTrichinellainEurope,anumberofoutbreakshaveoccurred

since 1975 (e.g.,inGermany,France,Italy,Spain,England,andPoland)affect-

inggroupsofpersonsofvarioussizes(thelargestabout650).Worldwide,

theannualincidencesper 100000 inhabitants(1 991 – 200 0)havevaried

widely,forexamplebetween0.0 1 inGermanyandtheUSA,5. 1 inLithuania,

and 11 .4inBulgaria.

Morphologyandlifecycle(Fig. 1 0. 18 ).MaleTrichinellaspiralisareapproxi-

mately 1 – 2 mmlong,thefemales 2 – 4 mm.Acharacteristicfeatureisthesub-

dividedesophaguswithamuscularanteriorportionandaposteriorpartcon-

sistingofglandularcells(“stichocytes”).TheotherTrichinellaspeciesareof

aboutthesamelengthanddonotshowmorphologicaldifferences,exceptT.

pseudospiralis,T.papuae,andTrichinellazimbabwensisthemusclelarvaeof

whichdonotencyst.

ThelifecycledescribedherereferstoT.spiralis.Infectionofhumansand

otherhostsresultsfromingestionofraworundercookedmeatcontaining

encystedTrichinellalarvae(Fig. 1 0. 16 e).Thelarvaearereleasedfollowing

exposuretothedigestivejuices,whereupontheyinvadeepithelialcellsin

thesmallintestine,reachingsexualmaturitywithinafewdaysafterfour

moltings.Themalessoondieaftercopulation,thefemalesliveforabout

fourtosixweeks.Eachfemaleproducesabout 200 – 1500 larvae(eacharound

100 lmlong),whichpenetrateintothelaminapropria.Thelarvaedisperse

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Kayser, Medical Microbiology © 2005 Thieme