Feb 12 - Viral Pathogenesis

Overview of Viral Entry Points

  • Focus on how viruses enter and infect human hosts.

  • Future discussions may cover the spread of viruses, considered an advanced topic.

Understanding Viral Hosts

  • Previous lectures discussed various hosts for viral replication: primates, cell cultures, and laboratory animals.

  • Today, consider humans as the hosts to understand viral infections.

Skin as a Barrier to Infection

  • Human skin acts as a primary barrier against viral infections.

    • Intact skin prevents viruses from entering unless broken (e.g. cuts or bites).

    • Epidermis consists of dead cells that do not support viral replication.

Concept of Inherent Infections

  • Introduced through a case study on the West Nile virus, first identified in 1999 in North America (New York City, Queens).

    • This virus belongs to the Flaviviridae family and includes others such as yellow fever and dengue viruses.

  • Important characteristics of the West Nile virus:

    • Positive strand RNA virus that requires no additional modifications for replication.

    • Enveloped virus with lipoproteins embedded within.

Historical Context of West Nile Virus Outbreak

  • Initial ignorance about the potential for West Nile virus in North America led to a lack of testing.

  • Public health response involved insecticide spraying to eliminate mosquito populations.

  • Social impact included major events being canceled due to the outbreak.

Viral Pathogenesis in Humans

  • Infection can lead to severe health issues if not contained by the immune system.

    • Diseases may result from the immune response rather than the virus itself.

  • Viremia observed as the virus travels through the bloodstream to infect other organs.

Entry Routes of Viruses into Humans

  • Entry points include:

    • Respiratory Tract:

      • Over 40 square meters of surface area allows for effective viral entry via droplets (coughing, sneezing).

    • Alimentary Tract:

      • Fecal-oral transmission can vary; viruses can survive different routes.

    • Neurogenic Tract:

      • Sexual transmission of viruses (e.g. HIV, HPV).

    • Conjunctiva:

      • Entry through rubbing of eyes leading to infections like adenovirus.

Example of Infectious Process Using Mousepox Virus

  • Mousepox virus was injected into the footpad of mice, leading to observable symptoms elsewhere on the body, indicative of systemic infection through viremia.

  • This experiment illustrates how a localized infection can disseminate throughout the body via the bloodstream.

Viral Shedding Mechanisms

  • Infected individuals can shed viruses via various routes (e.g. respiratory secretions, feces).

    • Sewage analysis can reveal presence of viruses affecting human populations (e.g. adenoviruses).

Impact of Environment on Virus Transmission

  • Environmental factors can influence transmission:

    • Aerosols can carry viruses over distances.

    • Raw sewage presents a risk for fecal-oral virus transmission.

Paradigm of Viral Entry and Amplification

  • Viral entry leads to replication, spread within the host, and potential to initiate an infection.

  • Each virus has unique entry mechanisms and characteristics that determine susceptibility and spread.

Case Study: Hepatitis A Virus Transmission

  • Hepatitis A virus (positive single strand RNA) linked to consumption of raw shellfish contaminated during collection by infected individuals.

  • Understanding of environmental factors and human behavior illustrates the mechanism of transmission during specific routine events (e.g. New Year's traditions in Southern Italy).

Conclusion

  • Recognition of how viruses exploit various entry points enhances our understanding of viral pathogenesis and public health responses.