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Questions and Answers
What are the two main components of a virus?
What are the two main components of a virus?
What term describes a complete virus particle that includes the genome and protective structures?
What term describes a complete virus particle that includes the genome and protective structures?
How does the size of viruses compare to the cells they infect?
How does the size of viruses compare to the cells they infect?
Which characteristic is NOT used to define virus families and species?
Which characteristic is NOT used to define virus families and species?
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What can be inferred from the ability of viruses to pass through filters designed to trap bacteria?
What can be inferred from the ability of viruses to pass through filters designed to trap bacteria?
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What type of envelope do many viruses possess?
What type of envelope do many viruses possess?
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What is a common feature that distinguishes different virus groups?
What is a common feature that distinguishes different virus groups?
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Which size range is typical for most viruses?
Which size range is typical for most viruses?
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What is the main structural feature that defines whether a virus is enveloped or naked?
What is the main structural feature that defines whether a virus is enveloped or naked?
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Which of the following is a feature of enveloped viruses?
Which of the following is a feature of enveloped viruses?
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Which virus family does Hepatitis B virus belong to?
Which virus family does Hepatitis B virus belong to?
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How are papovaviruses classified in terms of structure?
How are papovaviruses classified in terms of structure?
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What does the term 'antigenicity' refer to in the context of enveloped viruses?
What does the term 'antigenicity' refer to in the context of enveloped viruses?
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Which of the following is NOT included in the classification of medically important viruses?
Which of the following is NOT included in the classification of medically important viruses?
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Which virus is associated with progressive multifocal leukoencephalopathy?
Which virus is associated with progressive multifocal leukoencephalopathy?
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What characteristic do poxviruses exhibit compared to other virus families?
What characteristic do poxviruses exhibit compared to other virus families?
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What causes latent infections among the listed viruses?
What causes latent infections among the listed viruses?
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Which of the following viruses is an example of a human pathogen in the Hepadnaviruses family?
Which of the following viruses is an example of a human pathogen in the Hepadnaviruses family?
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What type of DNA is characteristic of adenoviruses?
What type of DNA is characteristic of adenoviruses?
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What is the primary visual feature that distinguishes poxviruses?
What is the primary visual feature that distinguishes poxviruses?
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Which family of viruses includes enteroviruses and rhinoviruses?
Which family of viruses includes enteroviruses and rhinoviruses?
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What type of capsid do caliciviruses possess?
What type of capsid do caliciviruses possess?
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Which human pathogen is associated with Epstein-Barr virus?
Which human pathogen is associated with Epstein-Barr virus?
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Which of the following statements about adenoviruses is true?
Which of the following statements about adenoviruses is true?
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Which virus has been classified into its own genus called hepevirus?
Which virus has been classified into its own genus called hepevirus?
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What is the primary human pathogen associated with reoviruses?
What is the primary human pathogen associated with reoviruses?
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Which group does the hepatitis C virus belong to?
Which group does the hepatitis C virus belong to?
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What type of RNA do retroviruses possess?
What type of RNA do retroviruses possess?
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Which of the following viruses is the main human pathogen under orthomyxoviruses?
Which of the following viruses is the main human pathogen under orthomyxoviruses?
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What is a characteristic feature of paramyxoviruses?
What is a characteristic feature of paramyxoviruses?
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Which family of viruses includes eastern and western encephalitis viruses?
Which family of viruses includes eastern and western encephalitis viruses?
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What property distinguishes orthomyxoviruses from paramyxoviruses?
What property distinguishes orthomyxoviruses from paramyxoviruses?
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Which virus is solely classified as a human pathogen among rhabdoviruses?
Which virus is solely classified as a human pathogen among rhabdoviruses?
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What is the primary structural characteristic of coronaviruses?
What is the primary structural characteristic of coronaviruses?
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Which disease is NOT caused by coronaviruses?
Which disease is NOT caused by coronaviruses?
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What does the term 'filo' refer to in the context of filoviruses?
What does the term 'filo' refer to in the context of filoviruses?
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What is the natural reservoir for the SARS-CoV virus?
What is the natural reservoir for the SARS-CoV virus?
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Which of the following diseases is characterized by a high fatality rate and originated in 2002?
Which of the following diseases is characterized by a high fatality rate and originated in 2002?
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Which feature is not true about rabies virus?
Which feature is not true about rabies virus?
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Which of the following statements about filoviruses is accurate?
Which of the following statements about filoviruses is accurate?
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What is the main mode of transmission of MERS to humans?
What is the main mode of transmission of MERS to humans?
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What is the incubation period for COVID-19?
What is the incubation period for COVID-19?
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Which symptom is NOT commonly associated with COVID-19?
Which symptom is NOT commonly associated with COVID-19?
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Which group of people is most likely to develop severe illness from COVID-19?
Which group of people is most likely to develop severe illness from COVID-19?
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What is another name for MERS coronavirus?
What is another name for MERS coronavirus?
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What percentage of people are expected to recover from COVID-19 without special treatment?
What percentage of people are expected to recover from COVID-19 without special treatment?
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What is the closest relative of MERS coronavirus?
What is the closest relative of MERS coronavirus?
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When was COVID-19 declared a pandemic by WHO?
When was COVID-19 declared a pandemic by WHO?
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Study Notes
Medical Important Viruses
- Viruses are infectious agents
- Composed of either RNA or DNA, but not both
- Also includes a protein-containing structure (capsid) to protect the genome
- Some viruses have additional features like an envelope with a lipid bilayer
- A complete virus particle is called a virion
- Viruses need host cells to reproduce
Virion
- A virion is a delivery system for the viral genome
- It protects the genome and enables the virus to bind to host cells
- May contain enzymes for initial steps in viral replication
- The pathogenicity of a virus depends on structural and functional characteristics
- Different species of viruses in a group can have varying clinical pathologies
Virus Structure
- Viruses are much smaller than cells; 100-1000 times smaller
- Smallest viruses are 20nm, and largest are about 300nm; overlapping with bacterial cells
- Pass through filters used for bacteria, supporting viral etiology
Virus Classification
- Viruses are categorized into families, subfamilies, genera, and species
- Based on viral nucleic acid type and structure
- Strategy of viral replication
- Symmetry of the viral capsid (structure of the protein shell)
- Presence or absence of a lipid envelope
Viral Genome
- Genomes can be DNA or RNA, either single or double stranded
- Common forms in nature are single-stranded RNA (ssRNA) and double-stranded DNA (dsDNA)
- Single-stranded RNA (ssRNA) genomes are subdivided into positive and negative polarity
- Positive polarity is used as a template for protein synthesis; negative polarity requires conversion
Capsid Symmetry
- The protein shell enclosing the genome has two geometric configurations
- Helical symmetry; rod or coiled shape
- Icosahedral symmetry; spherical or symmetric
Envelope
- An important structural feature used to categorize viruses
- The envelope is a lipid-containing membrane surrounding the nucleocapsid
- Viruses without envelopes are called naked viruses
- The envelope is derived from the host cell membrane
- Replaced by virus-specific proteins, imparting virus-specific antigenicity
Viral Replication
- Virus replication steps begin with attachment, penetration and uncoating of viral genome
- Gene expression and replication are followed by assembly and release of progeny viruses
- Not all the stages are the same across all types; some can change
Baltimore Classification
- This classifies medically important viruses into 7 groups
- Based on DNA or RNA, double or single stranded
- Positive (+) polarity or negative (-) polarity
- Other features like using reverse transcriptase also included
DNA Viruses
- Three naked, icosahedral families presented in order of increasing particle size
- Hepadnaviruses and herpesviruses are enveloped icosahedral viruses
- Poxviruses have a complex internal structure These families have several virus types (Parvoviruses, Papovaviruses, Adenoviruses)
Papovaviruses
- Naked icosahedral viruses with double-stranded circular DNA
- The name is an acronym of papilloma, polyoma, and SV40 viruses
Adenoviruses
- Naked icosahedral virus with double-stranded linear DNA
- Cause mild diseases like nose, mouth, pharynx infections
Hepadnaviruses
- Double-shelled viruses with icosahedral capsids enclosed by an envelope
- DNA is a double-stranded circle, unusual because complete strand is missing-
- Hepatitis B virus is the key pathogen in this family
Herpesviruses
- Enveloped viruses with icosahedral nucleocapsids, double-stranded linear DNA
- Cause latent infections
- Examples are Herpes simplex virus, Varicella-zoster virus, Cytomegalovirus, Epstein-Barr virus
Poxviruses
- Largest viruses with brick-like structures
- Envelope with unusual appearance, containing complex capsid symmetry
- Important members include smallpox and vaccinia viruses
RNA Viruses
- Three naked icosahedral families listed first, followed by enveloped icosahedral viruses
- Remaining families are enveloped helical viruses
- First five have single-stranded linear RNA, last three have single-stranded circular RNA
Picornaviruses
- Smallest RNA viruses (28nm in diameter)
- Single-stranded, linear, nonsegmented, positive-polarity RNA
- Naked icosahedral capsid
- Pathogens include poliovirus, coxsackievirus, echovirus, hepatitis A virus, and rhinoviruses
- Transmitted with contaminated food and water
Caliciviruses
- Naked viruses (38 nm diameter) with icosahedral capsids
- Single-stranded, linear, nonsegmented, positive-polarity RNA
- Common cold, and hepatitis E virus; contaminated water/food
Reoviruses
- Naked viruses (75nm in diameter); two icosahedral capsid coats
- Double-stranded linear RNA
- Respiratory enteric orphan viruses
- The main human pathogen is rotavirus, leading to diarrhea in infants
Flaviviruses
- Enveloped viruses, icosahedral capsid, single-stranded linear RNA
- Positive-polarity RNA
- Pathogens like hepatitis C, yellow fever, dengue, West Nile virus, St. Louis and Japanese encephalitis
Togaviruses
- Enveloped viruses, icosahedral capsid, single-stranded linear RNA
- Positive-polarity RNA
- Examples are alphaviruses and rubiviruses (Eastern and Western encephalitis viruses, rubella)
Retroviruses
- Enveloped viruses, icosahedral nucleocapsid, single-stranded linear RNA
- Positive-polarity RNA (but reverse transcriptase)
- Oncoviruses (sarcoma and leukemia viruses) and lentiviruses ("slow viruses") important pathogens
Orthomyxoviruses
- Enveloped viruses with helical nucleocapsids
- Eight segments of linear, single-stranded, negative-polarity RNA
- Major pathogen is influenza virus
Paramyxoviruses
- Enveloped viruses with helical nucleocapsids; single-stranded linear RNA
- Negative-polarity RNA
- Measles, mumps, parainfluenza, and respiratory syncytial viruses
Rhabdoviruses
- Enveloped viruses in bullet shape with helical nucleocapsids; single-stranded linear RNA
- Negative-polarity RNA
- The most important human pathogen is rabies virus
Filoviruses
- Enveloped viruses with helical nucleocapsids; single-stranded linear RNA
- Negative-polarity RNA
- Pathogens are Ebola and Marburg virus
Coronaviruses
- Enveloped viruses with helical nucleocapsids and single-stranded, linear, nonsegmented positive-polarity RNA
- The spikes around the surface give the appearance of a 'corona'
- Cause common cold, SARS, MERS and COVID-19.
Diseases
- Coronaviruses are a significant cause of common cold, often trailing in frequency only to rhinoviruses
- 2002: Severe acute respiratory syndrome (SARS) emerged
- 2012: Middle East respiratory syndrome (MERS) emerged
- 2020: SARS-CoV-2 and COVID-19 emerged
Prevention
- Washing hands frequently with water and soap or hand sanitizer
- Avoid contact with sick people
- Avoid touching eyes, nose, and mouth with unwashed hands
- Wear a mask in public situations
- Avoid crowded places
Molecular Tests
- Nucleic acid detection utilizing swabs or blood samples for diagnosis
- Antibody tests to detect immune response (serology) following exposure
COVID-19 Vaccines
- Multiple types of vaccines (mRNA, inactivated virus, viral vector, protein-based)
- Wide accessibility due to significant global research and collaboration
COVID-19 Variants
- Genetic variations arising in the virus over time
Summary of Viral Classifications and characteristics
- Viruses are classified based on their genome type (DNA or RNA), strandedness (single or double), the presence or absence of an envelope, and the symmetry of their capsid
References
- Various books on microbiology (e.g., from Lippincourt, Jawetz Melnick, and Adelbergs) and others
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Description
Test your knowledge on the fundamental concepts of virology including virus structure, classification, and key features that distinguish different virus families. This quiz covers essential topics that are crucial for understanding viruses and their interactions with host cells.
