Coronaviruses Quiz

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.