VIRUS-HOST INTERACTION | PARAMEDICS WORLD
VIRUS-HOST INTERACTION - WHAT HAPPENS WHEN VIRUS INTERACTS WITH LIVING HOST

VIRUS-HOST INTERACTION – WHAT HAPPENS WHEN VIRUS INTERACTS WITH THE LIVING HOST?

WHAT IS VIRUS-HOST INTERACTION?

⇒ All the processes that occur in the host body and viral particle after it enters the host body are called as virus-host interaction.

⇒ The virus-host interaction may cause different effects ranging from no apparent cell damage to rapid cell destruction.




CAUSES OF CELLULAR INJURY

⇒ Early or Non-structural viral proteins – shut down the host protein & DNA synthesis.

⇒ A large number of macromolecules – accumulates in host cells – distorts the cellular architecture & exerts a toxic effect.

⇒ Alterations in the permeability of plasma membrane – results in autolysis.

⇒ Alterations in the cytoplasmic membrane of the infected cell.

⇒ Damages the chromosomes of host cells.

⇒ Fusion of adjacent cell membrane – Syncytium formation.

VIRAL INCLUSION BODIES

⇒ These are the virus-specific intracellular globular masses which are produced during replication of the virus in host cells.

⇒ Inclusion bodies may be present in the cytoplasm, nucleus or both.

⇒ Intracytoplasmic inclusion bodies are found in:-

  • RABIES – Negri bodies
  • VACCINIA, VARIOLA – Guarneri bodies
  • MOLLUSCUM CONTAGIOSUM – Henderson-Patterson bodies
  • FOWL POX – Bollinger bodies

⇒ Intranuclear inclusion bodies are found in:- classified as Cowdry type A & B

                  Cowdry type A:-

  • HERPES – Lipschutz inclusions
  • YELLOW FEVER – Torres bodies

                  Cowdry type B:-

  • ADENOVIRUS – Basophilic bodies
  • POLIOVIRUS – Acidophilic bodies

⇒ Intracytoplasmic & Intranuclear inclusions are found in:-

  • MEASLES – Warthin-Finkeldey bodies

PATHOGENESIS OF VIRAL INFECTIONS

⇒ Depending on the clinical outcome, viral infections can be classified as follows:-

⇒ In apparent or subclinical infections

⇒ Apparent or clinical infections – Acute/Subacute/Chronic

⇒ Latent infection –

  1. Recurrent viral infections
  2. Slow viral infection
  3. Persistent tolerant viral infections
  4. Oncogenic viral infections

⇒ HIV virus leads to special type of latency – initially asymptomatic followed by progressive immune damage – secondary diseases – death after many years




ROUTES OF TRANSMISSION OF VIRUSES

⇒ Viruses enter the body through the following routes:-

⇒ Respiratory Tract, e.g. – Chickenpox, Influenza etc.

⇒ Alimentary Canal, e.g. – Enterovirus, Hepatitis viruses etc.

⇒ Skin, e.g. – Human Papillomavirus, Rabies virus, Vaccinia virus etc.

⇒ Genital Tract, e.g. HBV, HCV, HIV, HSV etc.

⇒ Conjunctiva, e.g. – Some Adenovirus & few Enteroviruses

⇒ Congenital, e.g. – Rubella, CMV, HIV, HSV etc.

HOST RESPONSE TO VIRUS INFECTION

⇒ The outcome of the virus infection is influenced by the virulence of the infecting strain and the resistance offered by the host

⇒ Mechanism of host resistance may be immunological or non-specific.

  1. Immunological resistance:-
    • Virions are good antigens and induce both humoral and cellular immune response –
      • HUMORAL RESPONSE:-
        1. In mediating humoral antiviral immunity, the important classes of antibodies are IgG, IgM & IgA.
        2. IgG & IgM plays a major role in blood and tissue spaces, IgA is more important on mucosal surfaces.
        3. Antibodies neutralize virus particle by several mechanisms:-
        4. May prevent adsorption of the virus to the cell receptor.
        5. Enhances virus degradation.
        6. Prevents the release of progeny virus from infected cells.
      • CELL-MEDIATED:- cell-mediated immunity is of critical importance in viral infections. The earliest indication of cell-mediated immunity in viral infections was the demonstration of delayed hypersensitivity following vaccination in immune individuals.
      • SUPPRESSION (exceptional case):- Some viral infections cause suppression of the immune response. For e.g. – HIV strikes at the center of the immune system by infecting the CD4+ helper T cells.
  2. Non – immunological resistance:-
    • These include:-
      • Phagocytosis
      • Body Temperature
      • Hormones
      • Malnutrition
      • Age
      • Interferons
    • Interferons are the family of host – coded proteins produced by cells on induction by viral or non-viral inducers.
      • The main biological effects of Interferons are as follows:-
        1. Antiviral effects:- Induction of resistance to infection
        2. Antimicrobial effects:- Resistance to intracellular infections, e.g. – Toxoplasma, Chlamydia, Malaria etc.
        3. Cellular effects:- Inhibition of cell growth & proliferation, DNA & Protein synthesis; increased expression of MHC antigens on the cell surface.
        4. Immunoregulatory effects:- The Enhanced cytotoxic activity of NK.K and T cells; activation of macrophage cytocidal activity; modulation of antibody formation; activation of suppressor T cells etc.



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