Influenza: Past, Present, and Future

Overview of Influenza

  • Definition: Influenza is a respiratory infection caused by influenza viruses, primarily spread through respiratory secretions (e.g., coughing, sneezing) between people.

  • Symptoms: Common symptoms include:

    • Fever

    • Non-productive cough

    • Chills

    • Runny nose

    • Sore throat

    • Body aches and headaches

  • Impact: Annually, influenza results in approximately:

    • 36,000 deaths in the U.S.

    • 200,000 hospitalizations in the U.S.

Historical Influenza Pandemics

  • Major historical pandemics include:

    • 1918 Spanish Influenza (H1N1): 30% of the global population infected with 20-50 million deaths, over 500,000 in the U.S.

    • Asian Influenza (H2N2) in 1957: Approximately 69,800 deaths in the U.S.

    • Hong Kong Influenza (H3N2) in 1968: About 33,800 deaths in the U.S.

    • 2009 H1N1 Pandemic: 60 million infected and 12,000 deaths in the U.S.

  • Definition of Pandemic: An outbreak that spreads across a large region, affecting people globally.

The Spanish Influenza of 1918-1919

  • Characteristics: The 1918 influenza virus was lethal and poorly understood due to limited virology knowledge at the time.

  • Fatalities in Brevig Mission, Alaska: 72 of 80 residents died; only one unaffected adult was present at the time.

Research on the 1918 Virus

  • Johan Hultin's Investigation (1951): Attempted to extract the influenza virus from mass graves in Brevig Mission but didn’t find viable samples.

  • Recreating the Virus: In modern research, having the nucleic acid sequence allows for the reconstruction of the influenza virus using plasmids, which aids in vaccine design.

    • Process: Involves using plasmids with influenza genes in a cell line to assemble a new infectious virus.

Advances in Molecular Virology

  • Dr. Jeffery Taubenberger's Research: Identified samples with likely influenza nucleic acids and sequenced them to study the reconstructed 1918 virus.

Recovery of the 1918 Virus: Findings

  • Avian Origins: The virus was found to replicate well in both the upper and lower respiratory facets and elicits strong inflammatory responses.

Vaccination and Immune Response

  • Annual Influenza Vaccination: Vaccines are designed to elicit protective immune responses against influenza. However, due to rapid changes in the virus, reinfections occur frequently.

  • Genome Characteristics: The influenza virus genome is comprised of segmented RNA with 8 separate RNA pieces, which contributes to its variability.

Mechanisms of Viral Change

  1. Antigenic Drift:

    • Gradual small mutations that accumulate over time due to the high mutation rate of the viral RNA polymerase.

    • Impacts vaccine effectiveness, requiring updates every few years.

  2. Antigenic Shift:

    • Abrupt major changes resulting from the reassortment of RNA segments when two distinct viruses infect the same cell.

    • Can lead to novel strains that generate pandemics, such as the 2009 H1N1 pandemic.

Current and Future Concerns: Avian Influenza

  • H5N1 Avian Influenza: Detected in humans since 1997 with a significant fatality rate (52% from known cases). Mostly associated with direct contact with poultry.

  • H7N9 Strain: Emerged in humans in February 2012 with limited human-to-human transmission.

  • Recent Findings: Bird flu has recently been found in mammals, raising concerns over potential pandemics.

Health Implications**

  • Surveillance and Control: The necessity for continued surveillance of both human and avian influenza strains to prevent potential pandemics.

  • Public Health Response: Incorporate vaccination and education strategies to mitigate outbreaks effectively.

Summary

Influenza, while a familiar illness, poses severe public health threats due to its potential for rapid mutation and pandemics. Understanding its transmission, historical impact, and mechanisms of change, alongside advances in research, can better prepare for and mitigate future outbreaks.