Week 3

Injury or death of the host cell caused by viral replication and release.
- Key Points:
- Viruses utilize host cell machinery for their replication, leading to potential damage or death of the host cell.

Viruses are considered acellular (not made of cells).
Fragile in the environment.
Can also refer to various viral classes:
- COVID-19
- Influenza
- Bacteriophages (viruses that infect bacteria)
Basic Structure of a Virus:
- Protein shell that protects the genome.
- Lipid membrane taken from the host cell.
- Contains genetic instructions (DNA or RNA).
Verbatim Definition: "A virus is a tiny infectious agent that… must enter a living cell to reproduce."

Virion: Complete, infectious viral particle (found inside or outside a host cell).
Capsid: Protein coat surrounding and protecting the viral genome.
Capsomeres: Repeating protein subunits that assemble to form the capsid.
- Examples include Influenza, Adenovirus, and RSV (Respiratory Syncytial Virus).
Bacteriophage: A virus that infects and replicates within bacteria.
General Notes:
- 🔴 RED NOTE: Antibiotics DO NOT work against viruses; prevention relies on vaccination and infection control.
- 🔴 RED NOTE: Enveloped viruses are generally easier to destroy with soap and alcohol than non-enveloped viruses.
- All viruses are smaller than bacteria and not considered alive outside a host cell.

Viruses exhibit various shapes and structures:
- Examples of shapes:
- Icosahedral (20-sided geometric shape, like Adenovirus).
- Helical (spiral shape, like Influenza).
- Complex forms (e.g., bacteriophages).
Structure's effects on viruses:
- Affects stability and susceptibility to disinfectants.
- Non-enveloped viruses require soap and water for effective cleaning, while alcohol alone is less effective.
Key Idea: Capsid shape affects infection control effectiveness and survival in the environment.

Classifies based on:
- Structure and genome.
- RNA or DNA (with subcategories such as double-stranded or single-stranded).
Baltimore Classification System: Explains viral replication strategy, which is crucial for understanding mutation, chronicity, and treatment options.
- High mutation rates, as seen in flu viruses, explain why flu vaccines need adjustments annually.
ICTV System: Official virus naming system that contributes to global scientific communication.

Some viruses replicate quickly, causing rapid disease spread and increased symptom severity.
- They can produce thousands of new viruses from one infected cell.
- Fast replication leads to potential mutations enabling immune detection evasion.
Chronic infections occur when viruses can evade immune responses or integrate into the host cell genome, as seen with HIV and hepatitis B.
Critical Thinking: Why do some infections become chronic or persistent?
- Possible causes include latencies, mutations, and immune evasion mechanisms.

The process leads to host cell damage and is significant for understanding symptoms and disease progression:
1. Entry: Virus enters the cell via endocytosis or membrane fusion.
2. Uncoating: Viral capsid is removed, releasing nucleic acid into the cell.
3. Replication: Genome copied using host and/or viral enzymes.
4. Assembly: New viral genomes and proteins are assembled into virions.
5. Release: Viruses exit the cell through lysis or budding, often causing cell damage.
Clinical Relevance:
- Understanding replication patterns provides insights into disease spread, acute symptoms, and infection control strategies.
- Mutations can affect treatment and prevention efforts.

Lytic (cytocidal): Functionality and morphology are affected, leading to immediate cell death. Examples include Rotavirus and Norovirus.
Persistent (chronic): Ongoing infections, where cells continuously produce the virus, like in Hepatitis C and some retroviruses.
Latent: Viruses remain dormant within the host but can reactivate later (e.g., Herpes Simplex Virus).
Transforming: Viruses cause ongoing cellular damage and can lead to cancer (oncogenic potential).

Types of damage caused by viral infections include:
1. Morphological effects (structural damage): Changes in shape, function, and membrane integrity (e.g., lysis).
2. Physiological effects (functional damage): Production of cellular proteins is inhibited, leading to failures in normal cell processes.
3. Biochemical/genotoxic effects: Can cause mutations and increase cancer risk (e.g., HPV).
4. Cell death: Can occur via necrosis or apoptosis.

Characteristics:
- Spread through fecal-oral route and are highly contagious.
- Often survive well on surfaces, necessitating strict infection control measures.
- Example: Norovirus, a significant cause of vomiting and diarrhea, requiring minimal infectious dose.

Positive PCR/NAAT tests indicate the presence of viral genetic material; interpretation requires the clinical context and associated symptoms.
- Understanding test results is essential for clinical decision-making and patient communication by nursing professionals.

Vaccines are crucial in preventing viral infections, including ensuring that immunity does not fade over time with boosters and managing circulating strains.
Important to communicate to patients why boosters are needed due to the nature of the virus's mutation and immunity decay.

Blood-borne viruses include Hepatitis B and C, which are preventable with safe practices and early treatment.
Nursing practices play a significant role in education, prevention, and mitigating the spread of blood-borne viruses through safe needle practices and patient education.

Viroids: Simple infectious agents that consist of small circular RNA, infect plants, and require a helper virus for replication.
Prions: Misfolded proteins that cause fatal brain diseases (e.g., Variant CJD). They lack nucleic acids, making them unique among infectious agents.
Requires special sterilization protocols due to their resistance to conventional sterilization methods.

Oncoviruses can disrupt normal cell cycles leading to cancer through mechanisms like disabling tumor suppressor genes.
Important for understanding the relationship between certain viral infections and cancer development.