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Questions and Answers
Which of the following coronaviruses is considered an alpha-coronavirus?
Which of the following coronaviruses is considered an alpha-coronavirus?
What percentage of human respiratory infections are attributed to HCoV-229E and HCoV-OC43 combined?
What percentage of human respiratory infections are attributed to HCoV-229E and HCoV-OC43 combined?
How are coronaviruses primarily transmitted?
How are coronaviruses primarily transmitted?
What is a significant characteristic of reinfection after a coronavirus infection?
What is a significant characteristic of reinfection after a coronavirus infection?
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During which season do coronavirus outbreaks primarily occur?
During which season do coronavirus outbreaks primarily occur?
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What is a characteristic feature of the RNA replication strategy in Coronaviridae?
What is a characteristic feature of the RNA replication strategy in Coronaviridae?
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Which of the following genera is NOT part of the Coronaviridae family?
Which of the following genera is NOT part of the Coronaviridae family?
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Which method do coronaviruses predominantly use to transcribe their full-length complementary RNA?
Which method do coronaviruses predominantly use to transcribe their full-length complementary RNA?
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How are coronaviruses classified within the order Nidovirales?
How are coronaviruses classified within the order Nidovirales?
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Which of the following statements is true regarding the subfamily Torovirinae?
Which of the following statements is true regarding the subfamily Torovirinae?
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What is the significance of high-frequency deletion mutations in coronaviruses?
What is the significance of high-frequency deletion mutations in coronaviruses?
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Which serogroups of human coronaviruses are represented by strains 229E and OC43?
Which serogroups of human coronaviruses are represented by strains 229E and OC43?
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What role does the rough endoplasmic reticulum play in coronavirus replication?
What role does the rough endoplasmic reticulum play in coronavirus replication?
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What component of the influenza virus is responsible for its antigenic variation?
What component of the influenza virus is responsible for its antigenic variation?
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Which of the following statements regarding influenza virus A is correct?
Which of the following statements regarding influenza virus A is correct?
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How many antigenically distinct types of neuraminidase are associated with the influenza virus?
How many antigenically distinct types of neuraminidase are associated with the influenza virus?
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What is the primary function of hemagglutinin in the influenza virus?
What is the primary function of hemagglutinin in the influenza virus?
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What describes the genome structure of the influenza virus?
What describes the genome structure of the influenza virus?
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How are influenza virus subtypes named?
How are influenza virus subtypes named?
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Which protein is NOT found as a surface antigen in the influenza virus?
Which protein is NOT found as a surface antigen in the influenza virus?
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Which of the following characteristics is true about influenza B virus?
Which of the following characteristics is true about influenza B virus?
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Which matrix protein of the Influenza A virus plays a role in forming an ion channel critical for virion uncoating?
Which matrix protein of the Influenza A virus plays a role in forming an ion channel critical for virion uncoating?
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What are the two lineages of Influenza B viruses?
What are the two lineages of Influenza B viruses?
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Which antigens are considered type-specific for influenza viruses?
Which antigens are considered type-specific for influenza viruses?
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What role does the NS 1 protein play in Influenza virus virulence?
What role does the NS 1 protein play in Influenza virus virulence?
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How does hemagglutinin facilitate the infection of a host cell?
How does hemagglutinin facilitate the infection of a host cell?
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Which of the following properties are characteristic of the M1 matrix protein?
Which of the following properties are characteristic of the M1 matrix protein?
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What is the purpose of the M2 matrix protein in the uncoating process?
What is the purpose of the M2 matrix protein in the uncoating process?
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Which statement about the group-specific antigens of influenza viruses is true?
Which statement about the group-specific antigens of influenza viruses is true?
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What is the primary function of hemagglutinin during the viral infection cycle?
What is the primary function of hemagglutinin during the viral infection cycle?
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What is the level of accuracy for rapid influenza tests in determining infection with the influenza virus?
What is the level of accuracy for rapid influenza tests in determining infection with the influenza virus?
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How does neuraminidase contribute to the viral life cycle?
How does neuraminidase contribute to the viral life cycle?
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What is the outcome of antigenic drift in orthomyxoviruses?
What is the outcome of antigenic drift in orthomyxoviruses?
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What type of antibodies primarily provides immunity in the respiratory tract against orthomyxoviruses?
What type of antibodies primarily provides immunity in the respiratory tract against orthomyxoviruses?
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What role does the matrix protein play in the assembly of orthomyxoviruses?
What role does the matrix protein play in the assembly of orthomyxoviruses?
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Which of the following drugs is effective only against influenza A viruses?
Which of the following drugs is effective only against influenza A viruses?
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Which statement correctly describes the process of viral mRNA translation?
Which statement correctly describes the process of viral mRNA translation?
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What is the role of neuraminidase inhibitors in treating influenza infections?
What is the role of neuraminidase inhibitors in treating influenza infections?
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What causes antigenic shift in orthomyxoviruses?
What causes antigenic shift in orthomyxoviruses?
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What challenge do existing influenza vaccines face?
What challenge do existing influenza vaccines face?
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At what point does the virion RNA polymerase function in the viral replication process?
At what point does the virion RNA polymerase function in the viral replication process?
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Which samples can be used for viral cultures to diagnose influenza?
Which samples can be used for viral cultures to diagnose influenza?
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Which statement is true about the blood tests for influenza antibodies?
Which statement is true about the blood tests for influenza antibodies?
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Where does the final step of virion release occur in the host cell?
Where does the final step of virion release occur in the host cell?
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Which of the following best describes the vaccines used against influenza?
Which of the following best describes the vaccines used against influenza?
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Study Notes
RNA Viruses: Coronaviruses
- Coronaviruses are large, enveloped RNA viruses.
- Animal coronaviruses cause diseases in domestic animals, which can cause human infection.
- Human coronaviruses cause common colds (second in frequency only to rhinovirus) and gastroenteritis in infants.
- Human coronaviruses are difficult to culture.
- Worldwide spread.
Types of Coronaviruses
- SARS-CoV (2002): an atypical pneumonia, severe acute respiratory syndrome (SARS)
- MERS-CoV (2012): Middle East respiratory syndrome (MERS), severe pneumonia
- COVID-19 (2019): New severe respiratory infection with pneumonia and respiratory distress
- COVID-19 or SARS-CoV-2 is a new strain of coronavirus
Structure and Composition
- Coronaviruses are enveloped, 120-160 nm particles
- Helical nucleocapsid is 9-11 nm in diameter
- 20-nm club- or petal-shaped projections are widely spaced on the outer surface of the envelope (a "solar corona").
- Two serotypes: 229E and OC43
- Nonsegmented, single-stranded, positive-polarity RNA genome
Replication
- Virus replicates in the cytoplasm
- Virus attaches to receptors on target cells by glycoprotein spikes (either S or HE)
- Functional receptor for SARS-CoV is angiotensin-converting enzyme 2 (ACE-2)
- SARS-CoV binds to CD-26 on the respiratory mucosa.
- Receptor for human coronavirus 229E (aminopeptidase N)
- The S glycoprotein may cause fusion of the viral envelope with the cell membrane, leading to uncoating.
- Requires pH 6.5 or higher
- Newly synthesized genomic RNA molecules interact in the cytoplasm with the nucleocapsid protein to form helical nucleocapsids.
- Nucleocapsids bud through membranes in the rough endoplasmic reticulum and the Golgi apparatus.
- Coronaviruses exhibit a high frequency of mutation and deletion during replication.
- This is unusual for an RNA virus with a non-segmented genome, contributing to the evolution of new virus strains.
Classification
- The Coronaviridae family is classified within the order Nidovirales.
- Two subfamilies: Coronavirinae and Torovirinae
- Six genera exist: Alphacoronavirus, Betacoronavirus, Gammacoronavirus, Deltacoronavirus, Bafinivirus, and Torovirus
- Characteristics used to classify Coronaviridae include particle morphology, unique RNA-replication strategy, genome organization, and nucleotide sequence homology.
- Two serogroups of human coronaviruses which are represented by strains 229E and OC43.
- SARS virus can be placed in the same group (group 2) as OC43.
- A third distinct antigenic group contains the avian infectious bronchitis virus of chickens.
- Seven coronaviruses are known to infect humans.
Epidemiology
- Coronaviruses are distributed worldwide.
- Outbreaks primarily occur in the winter on a 2-3 year cycle.
- They are transmitted by respiratory aerosol.
- Infection is typically limited to the mucosal cells of the respiratory tract.
- Approximately 50% of infections are asymptomatic.
- Immunity following infection appears to be brief, and reinfection can occur.
Origin Stories
- SARS-CoV: Originated in horseshoe bats.
- MERS-CoV: Originated in bats and became widespread in camels.
- COVID-19: Originated in horseshoe bats and a pangolin may have been an intermediate host.
Diagnosis
- Combination of symptoms, risk factors, and a chest CT
- RT-PCR from a nasopharyngeal swab
Treatment/Prevention
- No proven antiviral treatment for human coronavirus infections.
- Potential drugs like Ribavirin (for RSV and HCV), protease inhibitors, and Remdesivir.
- There are several vaccines.
- Inactivated influenza A and B virus vaccines are licensed for parenteral use in humans.
Immunity
- Immunity develops but is not absolute.
- Immunity against the surface projection antigen is most important
- Resistance to reinfection may last several years
- Reinfections with similar strains are common
- 95% of patients with SARS or MERS developed an antibody response
Prevention
- Frequent hand washing
- Social distancing
- Covering coughs and sneezes
- Keeping unwashed hands away from the face
- Using of masks for those who suspect they have the virus
- Management with symptom treatment, supportive care, isolation, and experimental measures
Coronavirus COVID-19
- Caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) identified in Wuhan, China in late 2019.
- The disease spread globally, resulting in a pandemic.
- Common symptoms include fever, cough, and shortness of breath, muscle pain, sputum production, diarrhea, sore throat, loss of smell, and abdominal pain.
- Symptoms, depending on the viral dose and immune status of the host typically appear abruptly and lasts 3-5 days.
ORTHOMYXOVIRUSES
- Influenza viruses are a major cause of respiratory disease.
- High frequency of genetic reassortment and resultant antigenic changes makes them difficult to control.
- Influenza is of three Types: A, B and C. A is most common and usually causes epidemics.
- Influenza A virus undergoes shifts and drifts with HA and NA.
- The two surface antigens of influenza undergo antigenic variation independent of each other.
- Type A has subtypes.
Replication
- The internal ribonucleoprotein complex is the group-specific antigen (influenza A, B, C).
- The hemagglutinin and neuraminidase are the type-specific antigens on the surface
- Influenza viruses have both group-specific and type-specific antigens.
- The virus adsorbs to host cell sialic acid receptors and enters cells in vesicles.
- The virion RNA polymerase transcribes the eight genome segments into eight mRNAs in the nucleus.
- Most of the mRNA that moves to the cytoplasm, where they are translated into viral proteins.
- Some of the viral mRNA remain in the nucleus, which serves as the template for the synthesis of the negative-strand RNA genomes in the progeny virions.
- The helical ribonucleoprotein assembles in the cytoplasm
- Matrix protein mediates the interaction of nucleocapsid with envelope.
- The virion releases from the cell by budding from the outer cell membrane.
- Minor antigenic changes are termed antigenic drift while mutations in the gene domain, that result in amino acid change, are termed antigenic shift
Other important facts
- Viruses can survive on surfaces for up to 72 hours
- The incubation period is 2-14 days (average 5 days)
Complications
- Reye's syndrome.
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Test your knowledge on coronaviruses with this quiz! Explore key facts about alpha-coronaviruses, transmission methods, and seasonal outbreaks. Enhance your understanding of these important respiratory pathogens.
