RNA Viruses

RNA Virus Table

(+) Strand RNA
Picornavirus
	Disease	Treatment or Vaccine
Poliovirus	Paralytic poliomyelitis (paralysis)Aseptic meningitis Post-polio syndrome	Sabin vaccine (live)SalK vaccine (Killed)
Rhinovirus	Common cold (most common cause)	No specific treatment
Coxsackievirus	Aseptic meningitis CarditisHand, foot, and mouth diseaseHerpangiaPleurodyniaBornholm disease (Devil’s grip)	No specific treatment
Echovirus	Aseptic meningitis	–
Hepatitis A virus	Mild acute hepatitis	Killed vaccineSerum globulin
Calicivirus
Norwalk virus	Acute gastroenteritis (schoolchildren)	No specific treatment
Togavirus
Rubella virus	Rubella (German measles)Congenital rubella	Live attenuated vaccine (MMR)
Eastern equine encephalitis	–	Killed vaccine
Western equine encephalitis	–	Killed vaccine
Flavivirus
Yellow fever virus	Yellow fever	Live attenuated vaccine
Dengue	Dengue (“break bone fever”)	Supportive only
Hepatitis C virus	Chronic hepatitis	IFNRibavirin
West Nile virus	Aseptic meningitisEncephalitisParalysis	Supportive only
St. Louis encephalitis	Encephalitis	Supportive only
Coronavirus
Coronavirus	Common coldSARS	Self-limiting
Retrovirus
HIV	AIDS	HAART
Human T cell leukemia virus	T-cell leukemia	–
Hepevirus
Hepatitis E virus	Mild acute hepatitis (fatal when prEgnant)	Self-limiting

(-) Strand RNA
Bunyavirus
Hantavirus	Hantavirus pulmonary syndrome (50% mortality)	Supportive only
CA Encephalitis virus	Encephalitis	–
Orthomyxovirus
Influenza virus	Flu	Zanamivir/oseltamivir
Paramyxovirus
Rubeola	Measles	Live attenuated vaccine (MMR)
Mumps virus	Mumps	Live attenuated vaccine (MMR)
RSV	Pneumonia (infants)	Palivizumab
Parainfluenza	CroupBronchiolitisPneumonia	Supportive only
Rhabdovirus
Rabies virus	Rabies	hRIG
Arenavirus
Lassa fever virus	Hemorrhagic fever (50% mortality)	Ribavirin
Lymphocytic choriomeningitis virus (LCMV)	Meningitis	–
Filovirus
Ebola and marburg viruses	Hemorrhagic fever (up to 90% mortality)	Supportive only

Double-Stranded (ds) RNA
Reovirus
Reovirus	Common coldGastroenteritis	Self-limiting
Rotavirus	Gastroenteritis (infants)	Self-limiting
Colorado tick fever virus	Flu-like	Supportive only

Virus Overview

Viruses are obligate intracellular infectious agents with the following basic components
- DNA or RNA
  - never both
- capsid
  - a protein coat that surrounds the genetic material
  - icosahedral or helical symmetry
  - made of capsomers
    - polypeptide chains organized into a globular subunit
    - in helical symmetry, capsomers are bound to RNA and coiled
      - forms a helical nucleoprotein capsid
- sometimes an envelope
Viruses are classified by
- nucleic acid
  - DNA or RNA
  - double stranded or single stranded
  - (+) or (-) stranded RNA
  - single or segmented pieces of nucleic acid
  - complexity of genome
- capsid
  - icosahedral or helical
- envelope
  - naked
    - DNA or RNA + capsomers and other structural proteins = nucleocapsid
  - enveloped
    - nucleocapsid + host membrane with viral-specified glycoproteins = enveloped virus
- size
  - diameter or number of capsomers
- ploidy
  - all viruses are haploid (1 copy of DNA or RNA)
  - except retroviruses
    - retroviruses have 2 identical copies of their ssRNA, approximating diploidy
- infectivity of purified nucleic acid
  - purified nucleic acid that is intrinsically infectious
    - dsDNA from most viruses
      - except poxviridae
      - except HBV
    - (+) strand ssRNA from most viruses
      - (+) linear, nonsegmented ssRNA can be translated immediately into a large protein by host machinery
      - virus must carry protease to cleave the 1 large protein product that will be generated by the host machinery
  - purified nucleic acid that is NOT intrinsically infectious
    - (-) ssRNA
      - viruses must carry an RNA-dependent RNA polymerase to generate mRNA the host machinery can read
    - dsRNA
they require enzymes contained in the complete virion for infectivity

RNA Viruses

Most RNA viruses
- are single-stranded (ssRNA, like human mRNA)
- have helical symmetry
- replicate in the cytoplasm
- are enveloped
Exceptions
- double-stranded (dsRNA)
  - reo
- icosahedral
  - reo
  - picorna
  - toga
  - flavi
  - calici
- replicate in nucleus
  - retro
  - orthomyxo
- non-enveloped
  - picorna
  - calici
  - reo
  - hepe

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