Viral Structure and Function Quiz

MABS Microbiology

• Course covers virology, respiratory viruses, hepatitis viruses, papilloma and polyoma viruses, and human retroviruses.

Course Instructional Objectives

• MCRO 3.1: Students will describe the taxonomy, structure, and function of coronaviruses, including transmission, pathogenesis, stages of viral infection, viral gene expression, viral replication, effects at the cellular level and/or human immune response.
• MCRO 3.2: Students will describe the taxonomy, structure, and function of influenza viruses, including transmission, pathogenesis, stages of viral infection, viral gene expression, viral replication, effects at the cellular level, human immune response and treatment
• MCRO 3.3: Students will describe the taxonomy, structure and function of RSV, including transmission, pathogenesis, effects at the cellular level, and human immune response.
• MCRO 3.4: Students will describe the taxonomy, structure, and function of adenoviruses, including transmission, pathogenesis, viral gene expression, viral replication, effects at the cellular level and/or human immune response.
• MCRO 3.5: Students will describe the taxonomy, structure, and function of retroviruses, especially HIV-1, including transmission, pathogenesis, stages of viral infection, viral gene expression, viral replication, effects at the cellular level, and human immune response and/or treatment.
• MCRO 3.6: Students will describe the taxonomy, structure, function of papillomaviruses, including transmission, pathogenesis, stages of viral infection, viral gene expression, viral replication, and the likelihood of HPV to cause cancer.
• MCRO 3.7: Students will describe the taxonomy, structure, and function of hepatitis viruses, focusing on transmission, pathogenesis, and cellular effects.

Review: Components of a Virus

• Viral Component: Nucleic acid, Capsid, Structural proteins, Non-structural proteins, Envelope.
• Role in Viral Life Cycle: Encodes information for progeny virions, protein shell protecting nucleic acid, contains/packages viral nucleic acid, form capsid, package genome, and/or attachment proteins, required for replication, for assembly, or facilitate disease progression, lipid bilayer for viral attachment, penetrates host cell membrane.
• Example: DNA or RNA, icosahedral, helical, complex, Matrix, nucleocapsid, VP, Polymerase, helicase, protease, transcription factors.

Respiratory Viruses

• Respiratory disease accounts for ~75-80% of acute morbidity in the United States.
• Most illnesses are viral, typically transmitted by respiratory droplets or hand-transfer.
• Incubation period is generally 1-4 days, but up to 14 days.
• The viruses commonly associated with acute respiratory disease (ARD) include parainfluenza viruses, influenza viruses, respiratory syncytial virus (RSV), coronaviruses, adenoviruses, rhinoviruses, human metapneumovirus (hMPV), and bocaviruses.

Overview: Coronaviruses

• Coronaviruses are large RNA viruses with a helical nucleocapsid and a lipid bilayer envelope.
• Viral Spike (S) glycoprotein, membrane, and envelope glycoproteins are essential.
• Replication occurs in the cytoplasm, acquiring an envelope from ER-Golgi membranes.
• Three novel coronaviruses have been identified: SARS-CoV-1, MERS-CoV, and SARS-CoV-2 (COVID-19).
• COVID-19, while initially limited, became a pandemic.

Respiratory Epithelium

• Upper respiratory tract epithelium is composed of taller, ciliated epithelial cells, with mucus-producing cells.
• Aids in debris clearance within inhaled air.
• Lower respiratory tract epithelium is composed of shorter, non-ciliated cells to facilitate better O2 & CO2 diffusion.

SARS-CoV-2

• SARS-CoV-2 enters the body through the respiratory tract (nasopharynx, oropharynx), airways, and alveolar epithelial cells.
• Viral Spike (S) glycoprotein's RBD interacts with ACE2 receptor.
• ACE2 receptors are in the respiratory system, kidney, and myocardium.

Coronavirus Characteristics

• Linear, positive sense ssRNA
• Envelope with club-shaped protein peplomers, which protect against acidic conditions (unique among enveloped viruses).

Viral Infection and the Immune System

• The body's innate immune response involves phagocytes, T-cells, and the release of cytokines.

Immune System & Coronaviruses

• Recruited leukocytes (lymphocytes, monocytes, and neutrophils) are essential immune responses to viral infections.
• Cell-mediated immunity plays a role in controlling severe and reducing viral infection, though antibody-mediated can result in more lingering protection.
• Viral infections can lead to tissue damage which, in turn, makes the body more susceptible to bacterial infections.

Influenza Virus

• Influenza is classified into three types (A, B, and C), based on antigenic differences.
• Influenza A viruses cause more extensive epidemics than other subtypes.
• Influenza B viruses are more stable and cause more localized outbreaks.
• Influenza C, less frequent, commonly affects humans and pigs.

Pathogenicity and Virulence

• Pathogenicity describes a microbe’s ability to cause disease within a person.
• Virulence describes the degree of pathogenicity among strains of the same microbe.

Antigenic Shift vs. Antigenic Drift

• Antigenic drift: Gradual, slight changes in viral surface proteins (HA & NA) due to mutations, resulting in less effective antibodies.
• Antigenic shift: Abrupt, major changes in viral surface proteins via re-assortment of the viral genome from different sources (typically host exchange from animals).

Influenza Virus Summary

• Family is Orthomyxoviridae.
• Genome is linear ssRNA.
• Enveloped with helical capsid.
• Transmission is by respiratory droplets.
• Tropism primarily affecting respiratory tract epithelium.
• Major surface glycoproteins are HA (hemagglutinin) and NA (neuraminidase)
• 18 HA and 11 NA subtypes are known, and some cause significant human disease.

Influenza Life Cycle

• Viral RNA transcription and genome replication occur in host cell's nucleus.
• Nucleocapsids assemble in the nucleus, then assemble/bud from plasma membrane in cytoplasm.

Influenza Disease

• Can cause different degrees of severity, from mild cold to fatal pneumonia.
• Severity can be influenced by pre-existing immunity and the specific influenza strain.

Influenza Treatment and Prevention

• Symptomatic treatment (e.g. acetaminophen, antihistamines).
• Antiviral medication (e.g. amantadine, rimantadine, oseltamivir, zanamivir) can be effective if given early.
• Prevention via vaccinations, which are updated to combat prevalent strains.

Classification of RNA Viruses

• All RNA viruses are single-stranded, except for the Reoviridae family
• All negative sense RNA viruses are enveloped with helical capsid structure.
• All non-enveloped RNA viruses have an icosahedral capsid.

Paramyxoviridae (e.g., Respiratory Syncytial Virus (RSV))

• RSV primarily infects bronchi, bronchioles, and alveoli of the lung, resulting in croup, bronchitis, or pneumonia in infants.
• RSV is spread via respiratory secretions and has an incubation period of 4-6 days.

Respiratory Syncytial Virus (RSV)

• Leading cause of fatal acute respiratory infection in infants and young children.
• Two serotypes circulating during the RSV season (October-March).
• Viral attachment proteins (attachment G glycoprotein and fusion F glycoprotein).
• Tropism is limited to the respiratory epithelium, with no viremia (absence of virus in the bloodstream).
• Transmission is through respiratory droplets and direct contact.
• At high risk include premature infants and elderly.

Adenovirus

• Adenoviruses are dsDNA viruses, generally non-enveloped, helical capsid.
• They are highly resistant to disinfectants.
• Frequently cause respiratory infections (types 1, 2, 3).
• Can cause conjunctivitis, and other non-respiratory infections.

Retroviruses

• Retroviruses are RNA viruses, using reverse transcriptase to convert their RNA genome into DNA during replication, and then are integrated into the host cell's genome.

Human Immunodeficiency Virus (HIV)-1

• A retrovirus, with two copies of positive-sense RNA.
• Viral attachment protein gp160 (gp120 + gp41)
• CD4 receptors are an initial target, along with co-receptors CCR5 and CXCR4 in cells (T-cells, macrophages, DCs).

Hepatitis Viruses

• A diverse group of viruses affecting liver inflammation, known for their variety regarding genomes (RNA or DNA viruses).
• A to E are caused by different viruses, with varied transmission routes, leading to acute or chronic illnesses.
• Hepatitis B is a DNA virus, while others are RNA.

Hepatitis A (HAV)

• Fecal-oral transmission of a picornavirus.
• Short incubation (~1 month).
• Primarily associated with acute hepatitis.
• No chronic sequelae (e.g. no long-term complications).

Hepatitis B (HBV)

• DNA virus (Hepadnavirus family).
• Primarily transmitted via body fluids (e.g. blood, sexual contact).
• Long incubation (3 months).
• Frequently resulting in chronic infections.
• Potential for severe complications, including cirrhosis and hepatocellular carcinoma (liver cancer)

Hepatitis C (HCV)

• RNA virus (Flavivirus).
• Transmitted through blood-to-blood contact.
• Long incubation (~6-7 weeks).
• Predominantly a chronic infection.
• High risk of cirrhosis and hepatocellular carcinoma.