Influenza A Virus Study Notes

Influenza A Virus Study Notes

Transmission Methods

• Airborne Transmission: Spread via respiratory droplets when an infected person coughs, sneezes, or talks.
• Surface Contamination: Virus can survive on surfaces for hours; transmission occurs through contact with contaminated surfaces followed by touching the face.
• Close Contact: Increased risk in crowded settings or close quarters.

Symptoms and Diagnosis

• Common Symptoms: Fever, chills, cough, sore throat, runny or stuffy nose, body aches, headaches, fatigue, and sometimes vomiting or diarrhea (more common in children).
• Diagnosis:
  • Clinical evaluation based on symptoms.
  • Laboratory tests (e.g., RT-PCR, rapid influenza diagnostic tests) for confirmation.

Vaccine Development

• Types of Vaccines:
  • Inactivated virus vaccines (shots).
  • Live attenuated virus vaccines (nasal spray).
• Annual Updates: Vaccines updated yearly to match circulating strains.
• Production: Usually involves egg-based or cell-based systems; recombinant DNA technology is also used.

Treatment Options

• Antiviral Medications:
  • Neuraminidase inhibitors (e.g., Oseltamivir, Zanamivir) reduce severity and duration of illness.
  • Polymerase inhibitors (e.g., Baloxavir) are newer options.
• Supportive Care: Rest, hydration, and over-the-counter medications for symptom relief.

Virus Mutation and Strains

• Mutation Rate: High due to RNA genome; leads to antigenic drift (small mutations).
• Strain Variability: Different strains categorized by surface proteins (hemagglutinin [H] and neuraminidase [N]); e.g., H1N1, H3N2.
• Pandemic Potential: New strains can emerge from animal reservoirs, leading to pandemics.

Genetics

• RNA Virus: Influenza A has a segmented negative-sense RNA genome.
• Segmented Genome: Allows reassortment during co-infection, leading to new strains.

Structure

• Surface Proteins: Hemagglutinin (H) for cell entry and neuraminidase (N) for viral release.
• Capsid: Enveloped virus with a lipid bilayer surrounding the RNA segments.

Replication

• Entry: Virus enters host cells through receptor-mediated endocytosis.
• Transcription and Translation: Viral RNA is transcribed into mRNA for protein synthesis.
• Assembly: New virions are assembled in the cytoplasm and bud off from the cell membrane.

Antigenic Shift

• Major Changes: Occurs when two different strains infect the same cell, leading to the mixing of RNA segments.
• Pandemic Risk: Can result in new subtypes that the population has little immunity against, potentially causing widespread outbreaks.

Transmission Methods

• Airborne transmission occurs through respiratory droplets from coughing, sneezing, or talking by an infected person.
• Surface contamination allows the virus to survive on surfaces for hours; infection can happen through contact followed by touching the face.
• Close contact in crowded settings significantly increases the risk of transmission.

Symptoms and Diagnosis

• Common symptoms include fever, chills, cough, sore throat, runny or stuffy nose, body aches, headaches, and fatigue. Vomiting or diarrhea is more prevalent in children.
• Diagnosis primarily relies on clinical evaluation based on the patient's symptomatology, with laboratory tests such as RT-PCR and rapid influenza diagnostic tests used for confirmation.

Vaccine Development

• Vaccines include inactivated virus vaccines administered by injection and live attenuated virus vaccines delivered via nasal spray.
• Annual updates to vaccines are essential to align with circulating influenza strains.
• Vaccine production typically involves egg-based or cell-based systems, with recombinant DNA technology increasingly utilized.

Treatment Options

• Antiviral medications like neuraminidase inhibitors (e.g., Oseltamivir and Zanamivir) are effective in reducing the severity and duration of influenza.
• Newer antiviral options include polymerase inhibitors such as Baloxavir.
• Supportive care focuses on rest, hydration, and over-the-counter medications to alleviate symptoms.

Virus Mutation and Strains

• Influenza A exhibits a high mutation rate due to its RNA genome, leading to antigenic drift from small mutations.
• Different strains are classified based on hemagglutinin (H) and neuraminidase (N) surface proteins, with notable strains like H1N1 and H3N2.
• The potential for pandemics arises from new strains emerging from animal reservoirs, which can create significant global outbreaks.

Genetics

• Influenza A is classified as an RNA virus with a segmented negative-sense RNA genome.
• The segmented genome facilitates reassortment during co-infection, contributing to the development of new strains.

Structure

• The virus's surface proteins include hemagglutinin (H) for facilitating cell entry and neuraminidase (N) for promoting viral release.
• Influenza A has an enveloped structure, with a lipid bilayer that encases its RNA segments.

Replication

• The entry of the virus into host cells occurs via receptor-mediated endocytosis.
• Viral RNA is transcribed into mRNA, which is essential for protein synthesis necessary for viral replication.
• New virions are assembled in the cytoplasm and subsequently bud off from the host cell's membrane.

Antigenic Shift

• Antigenic shift refers to significant genetic changes resulting from two different strains infecting the same host cell, leading to a mixed RNA population.
• This process can create new subtypes against which the population may have little pre-existing immunity, elevating the risk of widespread outbreaks.