Introduction to Virology

Introduction to Virology

• Viruses are the smallest microbes.
• They lack the characteristics of living things, except for the ability to replicate.
• Viruses are neither prokaryotes nor eukaryotes.

Viral Structure

• Viruses are made up of a core of genetic material (DNA or RNA) surrounded by a protein capsid.
• Sometimes, the capsid is surrounded by an additional spikey envelope.
• Viruses have proteins that help them bind to and enter host cells

Viral Replication

• Viruses make copies of themselves to regenerate.
• They acquire energy from their host cells.
• Viruses infect cells by inserting their genetic material into them.

Are Viruses Alive?

• Viruses are not considered alive because they have no cells and require a host cell to replicate.
• They use the host cell's mechanisms to reproduce.

Viral Infection

• A viral infection is the proliferation of a harmful virus inside the body.
• Viruses need a host cell to replicate.
• Viruses introduce their genetic material into host cells to produce more virus particles.

Active Viral Infection

• During an active viral infection, a virus makes many copies, causing the host cell to burst and release the new virus particles.
• The new virus particles can then infect other cells.

Symptoms of Viral Illness

• Symptoms of a viral illness arise from cell damage, tissue destruction, and the immune response.

Classification of Viruses

• Viruses are classified based on their nucleic acid (DNA or RNA).
• DNA viruses usually have double-stranded DNA (dsDNA), occasionally single-stranded DNA (ssDNA).
• RNA viruses typically have single-stranded RNA (ssRNA), sometimes double-stranded RNA (dsRNA).

Viral Transmission

• Transmission methods include: touch, droplets, airborne particles, contaminated food/water, contaminated needles, sexual contact, and insect vectors.

Respiratory Viral Infections

• Examples include Rhinovirus (common cold), influenza viruses, RSV
• Rhinovirus is responsible for most common colds.
• Influenza viruses are more severe than the common cold, including body aches and fatigue.

Seasonal Influenza

• More than 200,000 people in the US are hospitalized annually due to flu complications.
• Flu symptoms are more severe than colds.
• Influenza viruses belong to the Orthomyxoviridae family.
• Influenza viruses are classified based on nucleoproteins into types A, B and C; only A and B cause human disease.

Seasonal Influenza Variations (Delta, Omicron)

• Delta (B.1.617.2): Spreads easily, may be more severe, vaccines are effective, and treatments are available.
• Omicron (B.1.1.529): May spread easily, current severity is unclear, vaccines are effective but some antibody treatments may not be as effective.
• Fully vaccinated people can still spread the virus if infected.

Risk factors of Severe COVID-19

• Underlying conditions like older age, cardiovascular disease, chronic obstructive pulmonary disease, diabetes, and malignancy.
• Clinical presentations such as high fever, dyspnea, higher qSOFA score, and altered mental status.

COVID-19 Diagnosis

• Laboratory markers: Neutrophilia/lymphopenia, raised lactate dehydrogenase, raised C-reactive protein, raised ferritin, raised IL-6, raised ACE2, and D-dimer >1 µg/mL.
• Radiologic studies: Chest X-ray, Chest CT scan, and PCR.

Prevention of Viral Infections

• Frequent handwashing, social distancing, covering nose/mouth when coughing/sneezing, avoiding contact with infected individuals, disinfecting surfaces.

Respiratory Syncytial Virus (RSV)

• RSV can cause upper and lower respiratory infections, and symptoms mimic the common cold.

SARS-COV-2 (COVID-19)

• SARS-CoV-2 is a respiratory coronavirus.
• It caused a global pandemic in 2020.
• The virus is similar to SARS-CoV-1 and bat coronaviruses.
• The viral envelope contains spike, envelope, and membrane proteins.
• The virus binds to a host cell receptor via its spike protein.
• The S1 subunit of the S protein binds to ACE2 in the host cell.
• Symptoms of COVID-19 include cough, fever, shortness of breath, and pneumonia.

Discussed Topics

• General characteristics of viruses
• Viral structure
• Viral replication
• Viruses according to nucleic acid (DNA & RNA)
• Respiratory viral infections (Rhinovirus, Influenza, RSV)
• SARS viruses (COVID-19)

Explore the fascinating world of viruses, the smallest microbes that challenge our understanding of life. This quiz covers viral structure, replication, and the ongoing debate about whether viruses are alive. Test your knowledge on their unique characteristics and the impact they have on living organisms.