RNA Virus Classification Quiz

RNA Virus Classification

• Picornaviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has positive polarity. Important examples include poliovirus, rhinovirus, and hepatitis A virus.
• Hepeviruses are also non-enveloped viruses with an icosahedral capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has positive polarity. Hepatitis E virus is the primary medical example.
• Caliciviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has positive polarity. Norwalk virus is a significant example.
• Reoviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is double-stranded, linear, segmented, and contains 10 or 11 segments. Rotavirus is a major example.
• Flaviviruses are enveloped viruses with an icosahedral capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has positive polarity. Important examples include yellow fever virus, dengue virus, West Nile virus, and hepatitis C virus.
• Togaviruses are enveloped viruses with icosahedral capsid symmetry and an RNA genome that is single-stranded, linear, nonsegmented, and has positive polarity. Rubella virus is the most notable example.
• Retroviruses are enveloped viruses with an icosahedral capsid symmetry. Their genome is single-stranded, linear, and contains two identical strands (diploid). The polarity is positive. HIV and human T-cell leukemia virus are prominent examples.
• Orthomyxoviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, linear, segmented, and has negative polarity. Influenza virus is the primary example.
• Paramyxoviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has negative polarity. Significant examples include measles virus, mumps virus, and respiratory syncytial virus.
• Rhabdoviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has negative polarity. Rabies virus is the most notable example.
• Filoviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has negative polarity. Ebola virus and Marburg virus are prominent examples.
• Coronaviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, linear, nonsegmented, and has positive polarity.
• Arenaviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, circular, segmented, and has negative polarity. The two segments are connected by cohesive ends. Lymphocytic choriomeningitis virus is a significant example.
• Bunyaviruses are enveloped viruses with a helical capsid symmetry. Their genome is single-stranded, circular, segmented, and has negative polarity. The three segments are connected by cohesive ends. California encephalitis virus and hantavirus are notable examples.
• Deltaviruses are enveloped viruses with an uncertain capsid symmetry. Their genome is single-stranded, circular, and has a closed circle, negative polarity. Hepatitis delta virus is the primary example.

Viral Replication

• All viruses have one copy of their genome (haploid), except for retroviruses, which have two copies (diploid).
• Viruses replicate by entering host cells and utilizing their machinery (e.g., ribosomes, enzymes) to synthesize new viral proteins and replicate their genetic material.
• This process can be divided into early events, late events, and assembly/release.

Virus Structure

• Capsid: A protein coat that protects the viral genome from nucleases. It is composed of repeating subunits called capsomers.
• Nucleocapsid: The capsid and the enclosed nucleic acid.
• Icosahedral Capsids: Capsomeres are arranged in 20 triangles, forming a symmetric figure (icosahedron). This structure appears as an approximate sphere. All DNA viruses are icosahedral except poxvirus, which has a complex capsid.
• Helical Capsids: Capsomeres are arranged in a hollow coil that appears rod-shaped.
• Viral Proteins:
  • Surface proteins: Mediate attachment to host cell receptors and are targets of antibodies which inhibit viral replication.
  • Internal proteins: Include DNA or RNA polymerases.
  • Matrix protein: Connects the viral nucleocapsid and envelope proteins.
  • Superantigens: Non-specific T-cell activators produced by some viruses like Epstein-Barr virus and Cytomegalovirus.
  • Regulatory proteins: Control viral and cellular processes.
• Viral Envelope: Lipid bilayer containing viral glycoproteins and lipids derived from the host cell. The envelope is acquired as the virus buds off from the host cell.

Enveloped vs. Naked Viruses

• Enveloped Viruses: More sensitive to heat, drying, and disinfectants (alcohol, detergents) due to the presence of the lipid bilayer. Transmission typically occurs through blood and body fluids.
• Naked Viruses: More resistant to heat, drying, and disinfectants. Transmission often happens through indirect routes, like fecal-oral.

Viral Growth Curve

• Eclipse Period: The time during which no virus is found inside the cell. This ends with the appearance of new virus particles.
• Latent Period: The time from the onset of infection to the appearance of virus extracellularly.
• Viral Nucleic acid continues to function and begins to accumulate within the cell.
• Virus disappears and the virus particle is no longer detectable within the cell.

DNA Virus Classification

• Parvoviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is single-stranded, linear. B19 virus is a significant example.
• Polyomaviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is double-stranded, circular, supercoiled. Important examples include JC virus and BK virus.
• Papillomaviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is double-stranded, circular, supercoiled. Human papilloma virus is the primary example.
• Adenoviruses are non-enveloped viruses with an icosahedral capsid symmetry. Their genome is double-stranded, linear.
• Hepadnaviruses are enveloped viruses with an icosahedral capsid symmetry. Their genome is double-stranded, incomplete circular. Hepatitis B virus is the primary example.
• Herpesviruses are enveloped viruses with an icosahedral capsid symmetry. Their genome is double-stranded, linear. Herpes simplex virus, varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus are notable examples.
• Poxviruses are enveloped viruses with complex capsid symmetry. Their genome is double-stranded, linear. Smallpox virus and molluscum contagiosum virus are prominent examples.