General pathology of viral infections

GENERAL PATHOLOGY OF VIRAL INFECTION

Viral induced Cell Injury

  • Once a virus enters a cell the cell injury depends on the the nature of interaction between the cell and the virus

There are three types of cell injury:

  • Cytocidal
  • Infection with apparent pathological affect (Cytocidal)
  • Cell transformation (Non- cytocidal)

Cytocidal effect

  • Causes cell death or necrosis
  • Examples- Herpes virus, picorna virus, parvovirus , adeno viruses, flaviviruses
  • Capsid proteins produced by virus are toxic and affects host protein synthesis, DNA and RNA synthesis

Non- cytocidal effect

  • Causes cytopathic effect (CPE) which occurs in two forms

Persistent infection

  • Viral replication and release occurs without killing the cell by budding
  • Example –Arena virus and retrovirus

Chronic infection

  • Recovery from acute infection in which cell lysis occurs
  • Virus remains within cells
  • Reproduce at low levels
  • Chronic infection results in
    - Infectious carriers e.g. FMD
    - Chronic disease - e.g. African swine fever
    - Disease appearing after several years e.g. canine distemper

Slow viral infection: Viruses with long incubation period resulting in progressive fatal disease . Example-Lenti virus

Latent viral infection: Viral genome exists within the host but no viral replication occurs. Under suitable conditions the virus can be reactivated. Example- Herpes virus

Cell lysis due to immune response against virus infected cells

Both cytocidal and non cytocidal viruses express new antigens on the surface of infected cells that are recognised by the host as foreign and incite an immune response Example - Cytotoxic T lymphocytes and Natural killer cells. It is one of the most important defence mechanism

Cytopathic effect : (CPE)

Characterised by inclusion bodies

  • Inlcusion bodies are aggregates of virions and viral proteins
  • Intranuclear or intracytoplasmic or both
  • Basophilic or EosinophilicIntranuclear i/n- Herpes virus, adenovirus, parvovirus
  • Intracytoplasmic i/c- Pox virus, paramyxovirus, reovirus, rhabdovirus
  • Both i/n and i/c- Canine distemper, measles

Syncytia formation

  • Formation of multinucleated cells with single cytoplasm
    Examples - Herpes virus, paramyxo virus

Cell transformation

  • Certain viruses transform in vitro normal cells to cancer cells -Example- Oncogenic virus
  • DNA viruses- Polyoma virus, papillomavirus, hepatitis B viruses, herpes viruses
  • RNA viruses- Retro virus or oncorna viruses
Last modified: Saturday, 17 December 2011, 9:54 AM