Medical Microbiology

Nematoda(Roundworms) 603

Toxocara

Causativeagentoftoxocarosis

Distribution,lifecycle,andepidemiology.Dogs,cats,andfoxesalloverthe

world,especiallyyoungeranimals,arefrequentlyinfectedwithadultToxo-

cararoundworms.Theparasitesliveinthesmallintestineandinmostcases

producelargenumbersofeggs.Aninfectivelarvadevelopsinaneggshed

intotheenvironmentwithintwotothreeweeks.Humansareinfectedbyac-

cidentalperoralingestionofinfectiveeggs(geophagia,contaminatedfoods).

Smallchildrenrunaparticularlyhighrisk.Fairlyhighlevelsofcontamination

ofpublicparksandplaygroundswithToxocaraeggs(sandboxes>1–5 0 %)

havebeenfoundinmanycitiesinEuropeandelsewhere.Meanantibodypre-

valencelevelsofabout 1 – 8 %weremeasuredinhealthypersonsinGermany,

Austria,andSwitzerlandinserologicalscreeningbasedonaspecificELISA,

withfiguresashighas 30 %insomepopulationsubgroups.

Afterinfection,theToxocaralarvaehatchfromtheeggshellsinthesmall

intestine,penetratetheintestinalwall,andmigratehematogenouslyintothe

liver,lungs,CNS,eyes,musculature,andotherorgansystems.Larvaecaught

inthecapillaryfilterleavethevascularsystemandbegintomigratethrough

theorganinvolved.Thisresultsinhemorrhagesandtissuedestructionaswell

asinflammatoryreactionsandformationofgranulomatousfoci.Livinglarvae

areencapsulatedinconnectivetissueinallorgansexcepttheCNS,butthey

canalsoleavethecapsulesandcontinuemigrating.Thelarvaecanlivefora

numberofyears(atleast 10 yearsinmonkeys).DevelopmentofadultToxo-

carastagesinthehumanintestineisaveryrareoccurrence.

Clinicalmanifestations.VLMremainsinapparentinmostcases.Sympto-

maticcasesaremostfrequentlyobservedinchildrenagedtwotofiveyears.

Theclinicalsymptomsdependonthelocalizationanddegreeofpathological

changesandincludenonspecificandvariedconditionssuchaseosinophilia,

leukocytosis,hepatomegaly,brieffebrileepisodes,mildgastrointestinaldis-

orders,asthmaticattacks,pneumonicsymptoms,lymphadenopathy,urticar-

ialskinchanges,centralnervousdisorderswithparalyses,orepileptiform

convulsions.Eyeinfectionsareseeninallagegroupsandpresentasgranu-

lomatouschorioretinitis,cloudingofthevitreousbodyandotherchanges.

Oculartoxocariosisisoftenobservedwithoutsignsofvisceralinfection.

Diagnosis.Persistenteosinophiliaandtheothersymptomsdescribedabove

justifyatentativediagnosis.Etiologicalconfirmationrequiresserological

testingforspecificantibodies.Highlysensitiveandspecifictechniquesare

available(ELISA,Westernblot)(Table 11. 5 ,p.625).Positiveseroreactions

canbeexpectedfourweeksafterinfection.

10

Kayser, Medical Microbiology © 2005 Thieme