Laboratory Diagnosis of Viral Diseases: In-Depth Notes

Chapter Overview

  • Focus on laboratory diagnosis of viral diseases and working with viruses in research laboratories.

7.0 Definitive Laboratory Tests for Viral Diseases

  • Purpose of Lab Tests:
    • Manage patient treatments
    • Assess availability of antiviral medications
    • Support rapid advancements in drug therapies
    • Screen blood donors
    • Track and respond to novel viral strains
    • Implement disease-specific control measures and surveillance.

7.1 Proving Causation of Viral Diseases

  • Adapting Koch's postulates (used for bacterial diseases) presents challenges:

    • Viruses can have asymptomatic carriers
    • Subclinical infections complicate straightforward diagnosis.

  • Rivers’s 6 criteria for confirming viral causation:

    1. Isolate virus from diseased hosts.
    2. Cultivate virus in host cells.
    3. Prove filterability.
    4. Induce comparable disease in experimental models.
    5. Reisolate the virus from infected hosts.
    6. Document specific immune responses to the virus.

  • Advancements: Fredericks and Relman’s approach, utilizing biotechnology and PCR to refine causation guidelines.

7.2 Viral Diagnostics in the Clinical Laboratory

  • Over 60% of infectious diseases are viral.
  • Importance of accurate and rapid detection for effective treatment.
  • Factors affecting laboratory outcomes include:
    • Type and quality of specimen
    • Conditions and timing of specimen transport.

7.3 Storage and Collection of Biological Specimens

  • Varies based on suspected virus and symptoms.
  • Interaction process:
    • Patient visits doctor.
    • Tests ordered and interpreted by laboratories.
    • Results inform diagnosis and treatment.

Common Viral Infections and Specimen Collection

  • Diseases:
    • Respiratory (e.g., influenza)
    • Skin rashes (e.g., measles)
    • Central nervous system infections (e.g., rabies)
    • Hepatitis and other systemic infections.
  • Specimens:
    • Respiratory swabs, cerebrospinal fluid, serum, etc.

7.4 Five Approaches for Laboratory Diagnosis of Viral Infections

  1. Microscopy:

    • Light Microscopy for seeing cellular inclusions or using IHC.
    • Electron Microscopy to observe individual viruses.

  2. Viral Antigen Detection:

    • Techniques such as ELISA are rapid, inexpensive, and easy to perform.

  3. Culture:

    • Virus isolation through cell culture, observing cytopathic effects (CPEs).

  4. Nucleic Acid Detection:

    • NAATs like PCR and RT-PCR detect viral nucleic acids, aiding in diagnosis and monitoring (e.g., HIV, hepatitis).

  5. Antibody Detection:

    • Measures antibodies (IgM for recent infection, IgG for reinfection).
    • Methods: IFA, ELISA, Western blot.

7.5 Laboratory Safety

  • Laboratories classified by biosafety levels (BSL):
    • BSL-1: Minimum containment.
    • BSL-2: Increased precautions.
    • BSL-3: High containment protocols.
    • BSL-4: Maximum containment settings.