Lecture+5-+Influenza

Lecture Overview

  • Title: Lecture 5 - 1918 Influenza (Flu) and Other Influenza Pandemics

  • Instructor: Dr. Blanca Lupiani, VTPB 221

  • Date: September 3, 2024

  • Scope: Detailed examination of influenza pandemics focusing on the 1918 pandemic.

Learning Objectives

  • Understand genome organization and antigenic proteins of Type A influenza virus.

  • Explore the ecology of Type A influenza virus.

  • Discuss naming conventions of influenza viruses and their subtypes.

  • Explain antigenic shift and drift, and their involvement in seasonal and pandemic flu.

  • Describe clinical signs, transmission, and annual impact of influenza viruses.

  • Discuss the impacts of the 1918 flu pandemic in the US and its control measures.

  • Study current status of avian influenza and preparation of influenza vaccines.

  • Identify antiviral drug targets for flu treatment.

Influenza Virus Classification

  • Type A: Moderate to severe illness in all age groups; affects humans and animals.

  • Type B: Moderate illness; humans only.

  • Type C: Rare in humans; no epidemics.

  • Type D: Primarily affects cattle; not known to cause human illness.

Influenza A and B Viruses

  • Nature: RNA viruses with a genome consisting of 8 RNA segments.

  • Important Proteins:

    • Haemagglutinin (HA)

    • Neuraminidase (NA)

  • Subtypes:

    • Type A has various HA and NA subtypes.

    • Type B has variants but no subtypes.

Influenza Virus Replication Cycle

  1. Attachment: Virus binds to host cell.

  2. Endocytosis: Virus enters cell.

  3. Fusion/Uncoating: Viral RNA released into the cytoplasm for replication.

  4. Transcription & Translation: Viral proteins produced.

  5. Replication: RNA genome is replicated.

  6. Budding: New virions exit the cell.

Naming Influenza Viruses

  • Format: Type/Hemagglutinin/Neuraminidase/Location/Strain Number/Year

    • Example: A/duck/Alberta/35/76(H1N1)

  • Identification includes source, geographic origin, and strain characteristics.

Ecology of Influenza A Viruses

  • Natural reservoir in water birds; major subtypes represented.

  • Humans, mammals, and birds display combinations of HA and NA subtypes (e.g., H1N1, H3N2).

  • Notable: 1918 pandemic was due to an H1N1 strain.

Antigenic Drift vs. Antigenic Shift

  • Antigenic Drift: Small mutations leading to minor antigenic changes.

  • Antigenic Shift: Major changes via genetic reassortment (e.g. mixing of viruses in swine).

Clinical Signs of Influenza

  • Symptoms: Fever, chills, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis.

  • Severe cases in children may include gastrointestinal symptoms.

  • Typical resolution in 3-7 days, but cough and malaise can persist longer.

Transmission of Influenza

  • Mode of Transmission: Primarily through droplets and surface contact.

  • Contagious period generally lasts for 1 day before symptoms to 5-7 days after onset.

Impact of the 1918 Flu Pandemic

  • Affected 500 million people worldwide.

  • Led to 50 million deaths globally; 675,000 in the US.

  • Significant life expectancy reduction in the US (12 years).

  • High mortality in young adults (18-50 age group).

Control Measures during the 1918 Pandemic

  • Limitations: No vaccines or antibiotics available.

  • Control methods included isolation, quarantine, public hygiene recommendations, face masks, and limiting gatherings.

Future Insights

  • Advances in molecular biology are facilitating the study of 1918 strain characteristics and development of vaccines against broad influenza variants.

  • Vaccine Development: New strategies focus on broadly neutralizing antibodies targeting conserved regions of the virus.

  • Antiviral Drugs: Neuraminidase inhibitors like Tamiflu and novel approaches targeting polymerase activity.