Medical Microbiology

438 8 VirusesasHumanPathogen

Epidemiologyandprevention.Transmissionisbyfoodandwaterorinthe

formofsmearinfections.InfectionwithhepatitisAshowsaclearnorth–south

gradient:ithasbecomevirtuallyatravelers’diseaseincentralEurope.Im-

portedcasesfrequentlycauseminoroutbreaksinfamiliesorschools.Active

immunizationwithaninactivatedHAVvaccineisavailable.

Rhinoviruses

Pathogens.Thegenomicorganizationandreplicationsystemoftherhino-

viruses(1 17 serotypesfoundtodate)generallymatchthoseoftheentero-

viruses,althoughtheydifferinthattheyareacid-sensitiveandslightly

denser.

Pathogenicityandclinicalpicture.Therhinoviruses,thecausativepathogens

ofthecommoncold,infectthemucosaofthenasopharyngealspace(nose

andthroat).Theyremainstrictlylocalizedthereanddonotcausegeneralized

infections.Inrarecases,mainlyinchildren,theyareknowntocausebron-

chitisorbronchopneumoniaaswell.Theclinicalpictureisoftenworsenedby

bacterialsuperinfection.

Diagnosis.Laboratorydiagnosticsareonlyrequiredinspecialcasesofrhino-

virusinfection.Thevirusescanbegrownincellcultures.

Epidemiologyandprevention.Rhinovirusesaretransmitteddirectly,for

examplebycontaminatedhands,andpartlybydropletinfectionaswell.In-

fectivecontactsbetweenhumansappeartoinvolvemechanicalinoculation

(introductionintothenasopharyngealspacewithfingers).Rhinoviruses

occurworldwide,withpronouncedproliferationinthewintermonths.

Thefactthateveryonecomesdownwithcoldsrepeatedlyisexplainedby

theverybriefimmunityconferredbyinfectionandthemanydifferentviral

typesinvolved.Experimentshaveshownthattheinfectionsarealways

exogenous,i.e.,notreactivationsduetocold,wetness,etc.Theonlyconceiv-

ableprophylacticmeasureistoavoidlargegroupsofpeople.

AstrovirusandCalicivirus;HepatitisE

&Astroviruses,measuring 28 – 30 nmandcaliciviruses, 30 – 35 nm,areen-

teritispathogensinsmallchildren.Humanpathogensinthesegroupsinclude

theNorwalkvirusandhepatitisEvirus(HEV).Thelatteroccursepidemically

andendemicallyinAsian,CentralAmerican,andAfricancountries.Itistrans-

mittedbythefecal-oralroute,aboveallviadrinkingwater,andcausesrela-

tivelybenigninfectionsexceptinpregnantwomen.HepatitisEisconsidered

atraveler’sdisease. &

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Kayser, Medical Microbiology © 2005 Thieme