Virology Quiz on Viruses and Their Characteristics

Medical Important Viruses

• Viruses are infectious agents made of a genome (RNA or DNA, not both) and a protein-containing structure (capsid) to protect the genome.
• Some viruses have an additional lipid-containing envelope.
• A complete virus particle is called a virion, which acts like a delivery system for the genome.
• Viruses need a host cell to replicate, and the method of replication is intracellular.
• Viral pathogenicity depends on structural and functional characteristics, even within related virus groups.

Virus Structure

• Viruses are much smaller than cells (100-1000 times smaller).
• The smallest viruses are ~20nm in diameter, while the largest are ~300nm.
• This small size allows viruses to pass through filters designed to trap bacteria.

Viral Structure

• Viruses have a protein shell (capsid) which encloses the genome.
• The capsid may be helical (rod-shaped) or icosahedral (spherical).
• The capsid is composed of multiple copies of a single protein(or a few proteins), requiring limited genetic information.

Viral Genome

• Viral genomes may be RNA or DNA, either single-stranded (ss) or double-stranded (ds).
• ssRNA can be positive-polarity (messenger RNA sense) or negative-polarity (antisense).
• ssRNA viruses are most common.
• Positive-sense RNA can immediately be used as a template for protein synthesis, while negative-sense needs to be converted first.

Viral Capsid Symmetry

• The capsid, the protein shell encloses the genome.
• Viruses can be helical (rod-shaped) or icosahedral (spherical or symmetrical).
• The capsid is formed from multiple copies of a single polypeptide or a few different polypeptides.

Helical Symmetry

• Capsids with helical symmetry are similar to a cylinder, composed of repeating units of the same polypeptide. These units are bound together with hydrogen bonds.

Icosahedral Symmetry

• Icosahedral symmetry capsids are more complex.
• They are composed of multiple different polypeptide units called capsomers that arrange in an icosahedron shape.

Viral Envelope

• Some viruses have an envelope, a lipid-containing membrane acquired from the host cell.
• The envelope contains proteins that help the virus bind to host cells.
• Viruses without envelopes are called "naked" viruses.

Viral Replication

• The replication cycle begins with virus attachment to a host cell and leads to penetration and uncoating of the viral genome.
• Gene expression and replication follow uncoating, then assembly and release of viral progeny.

Baltimore Classification

• Viruses are classified into seven groups based on their genome structure and viral replication.
  • dsDNA viruses (herpes, adeno, pox, papova)
  • ssDNA viruses (parvo)
  • dsRNA viruses (reo, rota)
  • (+)ssRNA viruses (picorna, toga, flavi, corona)
  • (-)ssRNA viruses (rhabdo, orthomyxo, bunya, filo)
  • (+)ssRNA-RT viruses (retro, lenti)
  • dsDNA-RT viruses (hepadna)

Papoviruses

• Papovaviruses are nonenveloped, icosahedral viruses containing double-stranded circular DNA.
• They can cause different diseases in humans.

Adenoviruses

• Adenoviruses are nonenveloped, icosahedral viruses with double stranded linear DNA.
• They can cause various diseases in humans.

Hepadnaviruses

• Hepadnaviruses are enveloped viruses that appear roughly spherical and have a double shelled capsid with double-stranded DNA but a missing strand.
• Hepatitis B virus is a human pathogen in this family.

Herpesviruses

• Herpesviruses are enveloped with an icosahedral nucleocapsid and double-stranded linear DNA.
• They can cause latent infections.

Poxviruses

• Poxviruses are the largest viruses with a brick-like shape, an envelop, and have a complex capsid symmetry.
• They are responsible for skin lesions ("pocks.")

RNA Viruses

• RNA viruses are categorized into eight groups based on their properties.

Picornaviruses

• Picornaviruses are small, naked viruses with single-stranded RNA.
• They can cause various diseases in humans.

Caliciviruses

• Caliciviruses are naked viruses with single-stranded RNA and have an icosahedral capsid shape.
• Some can cause diarrhea.

Reoviruses

• Reoviruses are naked viruses with two icosahedral capsids and double-stranded RNA segments.
• Rotavirus causes diarrhea, mainly in infants.

Flaviviruses

• Flaviviruses are enveloped viruses with a single-stranded RNA and an icosahedral capsid.
• They cause yellow fever, dengue fever, West Nile virus, and Japanese encephalitis.

Togaviruses

• Togaviruses are enveloped viruses with a single-stranded RNA.
• Western and Eastern encephalitis are examples caused by these viruses

Retroviruses

• Retroviruses are enveloped viruses with single-stranded RNA.
• They contain the enzyme reverse transcriptase that transcribes RNA into DNA.

Paramyxoviruses

• Paramyxoviruses are enveloped viruses containing eight segments of single-stranded, negative-sense RNA in their helical nucleocapsid.
• They contain human Measles, Mumps, Parainfluenza, and Respiratory Syncytial viruses.

Rhabdoviruses

• Rhabdoviruses are enveloped viruses with a helical nucleocapsid and a single-stranded RNA.
• The only important human pathogen is Rabies virus.

Filoviruses

• Filoviruses are enveloped viruses with a helical nucleocapsid and a single-stranded RNA.
• Ebola virus and Marburg virus are the important human pathogens.

Coronaviruses

• Coronaviruses are enveloped viruses with a helical nucleocapsid and single-stranded RNA, and prominent spike proteins.
• Common cold, SARS, MERS and COVID-19 are diseases caused by these viruses

Medical Important Viruses Diseases

• Different types of coronaviruses are viruses can cause the common cold, SARS, MERS, and COVID-19.

COVID-19 Symptoms

• Common symptoms of COVID-19 include fever, tiredness, dry cough, aches, pains, nasal congestion, runny nose, sore throat, and diarrhea.
• Severe symptoms include difficulty breathing and high blood pressure.

Covid-19 Prevention

• Wash hands often, maintain physical distance, and wear a mask to help slow the spread of COVID-19.

Molecular Tests for COVID-19

• Nucleic acid detection tests use PCR to detect viral RNA in samples.
• Antibody tests detect the presence of antibodies to SARS-CoV-2.

COVID-19 Vaccines

• Several COVID-19 vaccines are available worldwide inactivated virus, mRNA, viral vector, and protein-based vaccines.

Virus Variants

• New labels and classification for SARS-CoV-2 variants based on their origin location are being assigned regularly.

Summary

• Viruses are primarily classified based on their DNA/RNA type and if the virus has an envelope.
• The summary emphasizes different RNA and DNA virus classifications, and examples.

Test your knowledge on various types of viruses, including their classifications, characteristics, and significant examples. This quiz covers enveloped and naked viruses, RNA types, and specific virus families, providing a comprehensive assessment of your virology understanding.