Medical Microbiology

380 7 GeneralVirology

Classification

&Thetaxonomicsystemusedforvirusesisartificial(i.e.,itdoesnotreflect

virusevolution)andisbasedonthefollowingmorphologicalandbiochem-

icalcriteria:

— Genome:DNAorRNAgenome(importantbasicdifferentiationofvirus

types!)aswellasconfigurationofnucleicacidstructure:single-stranded

(ss)ordouble-stranded(ds);RNAvirusesarefurthersubclassifiedaccord-

ingtoplusandminuspolarity(p. 38 3f.).

— Capsidsymmetry:cubic,helical,orcomplexsymmetry.

— Presenceorabsenceofanenvelope.

— Diameterofthevirion,orofthenucleocapsidwithhelicalsymmetry.

ViruseswithHelicalSymmetry

Ribonucleoprotein

a

Hämagglutinin Envelope

Neuraminidase

Protein

Lipid

Fig. 7. 3 aSchematicstructure

ofamyxovirus.

b Influenza viruses viewed

withanelectronmicroscope:

The ribonucleoprotein spiral

(nucleocapsid, NC) is visible

inside the partially removed

envelope(E).S=spikes.

7

Kayser, Medical Microbiology © 2005 Thieme