Virology Fundamentals Quiz

Introduction to Virology, Lecture 1

• The lecture is titled "Introduction to Virology, Lecture 1" and was delivered by Dr. Craig Thompson, Assistant Professor of Molecular Pathology at Warwick Medical School.
• Learning outcomes include describing key elements defining a virus, key experiments identifying viruses, the structure of viruses (with specific examples of influenza, varicella, and SARS-CoV-2), characteristics of the infectious cycle (examples of influenza, varicella, and SARS-CoV-2), viral infection terms (latency, chronic active, persistence), and the pathogenesis of viral infection (with emphasis on influenza and varicella).

Viruses

• Viruses infect all living things, and humans carry viral genomes as part of their genetic material.
• There are more than 10³⁰ bacteriophage particles in the world's waters.
• A bacteriophage weighs a femtogram (10^-15 g).
• The weight of all the people in the UK is 5.29 x 10⁹ kg.
• The weight of the population of Europe is 3.512 x 10¹⁰ kg.
• The weight of the world's population is 6.3 x 10¹¹ kg.

Viruses in a Liter of Seawater

• A liter of seawater contains more viruses than there are people on Earth.
• Abundance is measured by particle number.
• Viruses comprise a significant portion of both abundance and biomass in seawater.

Viruses – Infect Us

• Some viruses, like herpes simplex, varicella zoster, cytomegalovirus, Epstein-Barr virus, and human herpesviruses 6, 7, and 8, persist for life.
• The human virome lists specific virus types in various body fluids/organs.

Viruses – Disease

• Viruses cause a significant amount of human disease.
• Top causes of death worldwide in 2019 included cardiovascular diseases, cancers, respiratory diseases, digestive diseases, and lower respiratory infections, among others.
• Similarly, causes of death in children under five in 2019 included lower respiratory infections, neonatal preterm birth, neonatal asphyxia & trauma, and diarrheal diseases, among others.

Viruses - Key Examples and Information

• Annual deaths from influenza range from 250,000 to 600,000.
• SARS-CoV-2 caused approximately 3,000,000 deaths per year.
• HIV caused approximately 680,000 deaths per year.
• Flaviviruses caused approximately 100,000 deaths per year.
• Norovirus caused approximately 200,000 deaths per year.

Infectious Diseases Impact

• Infectious diseases have a significantly greater impact on lower and middle-income nations compared to higher-income countries.
• Leading causes of death in several income groups are noted. This includes communicable and non-communicable causes.

Gene Regulation and Viruses

• Much of the human genome consists of integrated retroviruses in the form of transposons, specifically LINES and SINEs.
• Viruses can insert themselves into the genome and regulate associated genes.
• The placenta is formed from a viral protein called syncytin.
• Viruses are being increasingly used as vaccine carriers (e.g., the ChadOx COVID-19 vaccine, based on an adenoviral vector).

The Role of Viral Gene Regulation

• Viral proteins are encoded by specific sections of viral genomes.
• LTRs, (long terminal repeats), gag, pol, env, and LTRs have important roles in viral gene regulation and co-option affecting placenta formation.

Key Experiments Identifying Viruses

• Charles Chamberlain's filter experiments showed that viruses are smaller than bacteria, requiring a host for replication, and are microscopic in size.
• The electron microscope allowed researchers to visualize viruses as microorganisms with organized proteins and nucleic acids.
• Hershey-Chase experiments demonstrated that DNA, not protein, is the heritable material of viruses, proving DNA is the genetic material.

Question 1: Microorganisms

• How scientists discovered that viruses were microorganisms relates to the early experimental methods and tools available.

The Structure of Viruses

• Viruses have a genetic core consisting of DNA or RNA. Viruses either have DNA or RNA, but never both.
• A protein coat, called a capsid, surrounds this core, with individual units called capsomeres.
• Some viruses have an envelope, a lipid layer surrounding the capsid.

Classification of Viruses

• Viruses are classified based on various features visualized with electron microscopy (e.g., adenoviruses, Ebola viruses, herpes viruses, SARS viruses).
• Examples of viruses illustrated in the classification include influenza, HIV, Papillomavirus, and more.

Influenza Virus

• An influenza virus contains antigenic sites on surface proteins (hemagglutinin and neuraminidase) vital for antibody recognition and neutralization when encountering influenza or influenza vaccine, preventing further infection.

Differences between Bacteria and Viruses

• Viruses are intracellular parasites, lacking ribosomes and metabolism; they rely on host cells.
• In contrast, bacteria are typically free-living, possess ribosomes, and have distinct metabolic processes.

Baltimore Classification

• This system groups viruses based on their genome type (DNA or RNA, single-stranded or double-stranded) & mRNA synthesis method.

Diversity of Viruses

• DNA viruses have structures including poxviruses, adenoviruses, herpesviruses, and more.
• RNA viruses have various structures, including coronaviruses, orthomyxoviruses, and retroviruses.

Question 2: Baltimore Classification of Influenza

• Influenza is classified as an RNA virus according to Baltimore classification.

The Infectious Cycle

• The infectious cycle encompasses all events within a virus-infected cell.
• This includes receptor binding, cell entry, viral genome replication, viral protein synthesis, and virion assembly followed by release.

Stages of Infection

• The infection process includes attachment and entry, translation, genome replication, and release phases.

Question 3 & 4: SARS-CoV-2 Entry Glycoprotein

• SARS-CoV-2 utilizes a specific glycoprotein (spike protein) and a receptor (ACE2) to enter host cells.

Viruses: Effects on Cells

• Viral infections can cause cell death (cytopathic effect), transformation into tumor cells, and persistent/latent infections.

Key Terms

• Susceptible cells have functional receptors for a specific virus.
• Resistant cells lack the necessary receptors.
• Permissive cells have the capability for viral replication.

Overview of Viral Infections

• Various viral infections impacting different parts of the human body are listed.

Viruses: Natural History of Infection

• Acute infections typically resolve swiftly, followed by immunity.
• Chronic infections persist, with either continuous viral replication or latency.

Viruses: Persistence

• Viruses may persist in host cells without causing cell death.
• The persistence occurs through integration of viral genomes into host cells, episomal circular molecules or avoidance of the host-immune system.