STEPTRACKERMICROBIOLOGY | VIRAL CLASSIFICATION | HIGH-YIELD REVIEW

Viral Classification Map

Every family on one page — genome, envelope, shape and the key members. Use it as the map before the DNA and RNA virus chapters.

FOCUS ON
Seven DNA families: herpes, hepadna, adeno, papilloma, polyoma, parvo, pox. Enveloped DNA: herpes, hepadna, pox. Naked RNA: picorna, calici, reo, hepevirus. + RNA: picorna, calici, flavi, toga, corona, retro. − RNA: orthomyxo, paramyxo, rhabdo, filo, arena, bunya, delta. Segmented: bunya, orthomyxo, arena, reo. Learn one prototype disease per family first, then the details in 6.01–7.08.
FAMILY
GENOME · ENVELOPE · SHAPE
KEY MEMBERS
NOTE
Herpesviruses
dsDNA linear · enveloped · icosahedral
HSV-1/2, VZV, EBV, CMV, HHV-6/7, HHV-8
Latency · envelope from nucleus
Hepadnavirus
Partly dsDNA circular · enveloped
HBV
Has reverse transcriptase (RNA intermediate)
Adenovirus
dsDNA linear · naked
Adenovirus
Conjunctivitis, pharyngitis, hemorrhagic cystitis
Papillomavirus · Polyomavirus
dsDNA circular · naked
HPV · JC, BK
Warts, cancer · PML, transplant nephropathy
Parvovirus
ssDNA linear · naked · smallest
B19
Erythema infectiosum, aplastic crisis, hydrops
Poxvirus
dsDNA linear · enveloped · complex, largest
Smallpox, vaccinia, molluscum, mpox
Cytoplasmic replication
Picornavirus
+ssRNA · naked · icosahedral
Polio, echo, rhino, coxsackie, hepatitis A
Polyprotein cleaved by viral protease
Calicivirus · Hepevirus
+ssRNA · naked
Norovirus · hepatitis E
Fecal-oral
Reovirus
dsRNA, segmented · naked · double capsid
Rotavirus
Infant diarrhea
Flavivirus
+ssRNA · enveloped
HCV, yellow fever, dengue, West Nile, Zika, Japanese encephalitis
Mostly arboviruses
Togavirus · Matonavirus
+ssRNA · enveloped
Chikungunya, EEE/WEE · rubella
Rubella now its own family (Matonaviridae)
Coronavirus
+ssRNA · enveloped · helical
Common cold coronaviruses, SARS-CoV-2, MERS
Largest RNA genome
Retrovirus
+ssRNA, diploid · enveloped
HIV, HTLV-1
Reverse transcriptase, integrase
Orthomyxovirus
−ssRNA, 8 segments · enveloped · helical
Influenza A, B
Replicates in nucleus
Paramyxovirus · Pneumovirus
−ssRNA, nonsegmented · enveloped · helical
Parainfluenza, mumps, measles · RSV, metapneumovirus
F (fusion) protein → syncytia
Rhabdovirus
−ssRNA · enveloped · bullet-shaped
Rabies
Negri bodies
Filovirus
−ssRNA · enveloped · filamentous
Ebola, Marburg
Hemorrhagic fever
Arenavirus · Bunyavirus
−ssRNA (ambisense), segmented · enveloped
LCMV, Lassa · hantavirus, Rift Valley, Crimean-Congo
Rodent-borne
Deltavirus
−ssRNA circular · uses HBsAg envelope
HDV
Needs HBV

Mechanism — envelope predicts transmission

Naked capsid
→
Survives acid, bile, drying
→
Fecal-oral, fomitesPolio, HAV, noro, rota, adeno
Lipid envelope
→
Destroyed by drying, detergents
→
Respiratory, sexual, blood, vectors

Naked vs enveloped at a glance

GENOME
NAKED
ENVELOPED
DNA
Papilloma, adeno, parvo, polyoma
Herpes, hepadna, pox
+ RNA
Picorna, calici, hepe
Flavi, toga, corona, retro
− RNA
—
All
ds RNA
Reo
—

How it's tested

COMMON CONFUSIONHBV is a DNA virus that uses reverse transcriptase; HIV is an RNA virus that makes DNA — both are targets for some of the same drugs (tenofovir, lamivudine).
THE TRAPEvery negative-sense RNA virus is enveloped — if a question describes a naked RNA virus, it's positive-sense or reovirus.
YOUR APPROACHPlace the virus on this map first; transmission, replication site and drug targets follow from its row.

If you see… think…

Bullet-shaped virus → rabies (rhabdovirus)
Filamentous virus causing hemorrhagic fever → Ebola, Marburg
Largest DNA virus, brick-shaped → poxvirus
Circular, partly double-stranded DNA with RT → HBV
Naked +RNA causing paralysis → poliovirus (picornavirus)
Segmented viruses → bunya, orthomyxo, arena, reo
Diploid RNA genome → retroviruses
Defective virus borrowing HBsAg → HDV
Syncytia from fusion protein → paramyxoviruses (RSV, measles)
Rodent-borne segmented viruses → arena (Lassa), bunya (hanta)