Medical Microbiology

456 8 VirusesasHumanPathogen

Pathogen.Thenamereovirusisderivedfromtheabbreviationforrespiratory

entericorphanvirus,recallingthatnodiseaseswereassociatedwiththevirus

uponitsdiscovery(hence“orphanvirus”).ThefamilyReoviridaeincludes,in

additiontophytopathogenicandzoopathogenicstrains,threegenerain

whichhumanpathogensareclassified:

— Coltivirusesincludealargenumberofpathogenssignificantinveterinary

medicineaswellasthehumanpathogenvirusthatcausesColoradotick

fever.

— Reovirusesinthenarrowersense,withthreeserogroups.

— Rotaviruses,groupsAtoF,furthersubdividedintosubgroups,serotypes,

andelectropherotypes(seebelow).Therotaviralgenomeconsistsofele-

vensegmentsofdouble-strandedRNA.Eachsegmentcodesforoneviral

protein.Somesegmentsinotherreovirusescodefortwoorthreeproteins.

Pathogenesisandclinicalpicture.

— Coltiviruses.Coloradotickfeverusuallyrunsamildcoursewithfever,

myalgias,nausea,andvomiting,rarelyencephalitis.

— Reoviruses.Implicationofthesevirusesindiseasesisstilluncertain.It

appearstheyarecapableofinfectingtherespiratoryandintestinaltracts

ofchildren.Thefactthattheyarealsofoundveryfrequentlyinasympto-

maticpersonsmakesitdifficulttocorrelatethemwithspecificclinical

pictures.

— Rotaviruses.Inthemid-seventiestheseviruseswererecognizedasdiar-

rhea-causingvirusesininfantsandsmallchildren(Fig.8. 15 ).Theyarethe

mostfrequentcauseofdiarrheainchildrenagedsixmonthstotwoyears.

Itwasrecentlydiscoveredthattheyalsoplayaroleininfectionsofthe

elderly,andaboveallinimmunosuppressedpatients(e.g.,bonemarrow

transplantpatients),andcancausesevereclinicalpicturesinthese

groups.Rotavirusesenterthebodyperosorbydropletinfection,replicate

inthevilliofthesmallintestineandcausediarrhea,potentiallyresulting

inexsiccosis.

Diagnosis.Coloradotickfevercanbediagnosedserologically.Reovirusinfec-

tionscanbediagnosedbyisolatingthepathogensincellcultures.Rotaviruses

donotreadilygrowincellculturesfordiagnosticpurposes.Theycanbede-

tectedmorereadilyunderanelectronmicroscopeorinantigenassaysusing

commerciallyavailablesolidphasetests(EIA)orpassiveagglutination.An

eleganttypingmethodforthedifferentrotavirusstrainsinvolvesanalysis

oftheelectrophoreticmobilityofthe 11 dsRNAstrandsoftheviralgenome.

Epidemiology.Humansarethesolenaturalreservoiroftheinfantpathogen

rotaviruses.Generalizedcontaminationispractically 100 %whenchildren

reachschoolage,butcarriersandreinfectionsarestillpossibledespiteim-

munity.Diarrhealinfectionsareamongthemostimportantcausesofdeathin

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Kayser, Medical Microbiology © 2005 Thieme