How do parasites survive inside an immunocompetent host ?

Ectoparasites
Infestation leads to local lesions of minor to moderate importance. This leads only to:
- allergic reactions (itching)
- immunological reactions (without result)
  
  None of these reactions really harm the parasite, but do harm the host
Intracellular parasites
These parasites try to escape any immunological reactions mounted by the host by hiding themselves inside the host cells where the immune system cannot reach them.
Examples are:
- Toxoplasma in lymphocytes,
- Plasmodium in erythrocytes,
- Leishmania, in macrophages,
- T.cruzi in muscle cells.
Extracellular parasites
- Some parasites cover their cell surface with host serum proteins to avoid recognition by the immune system of the host
  Examples are:
  - Schistosoma worms that cover themselves with host serum albumin
  - Rodent trypanosomes that cover themselves with ablastin (IgE)
- Antigenic variation in the African trypanosomes that live freely in the bloodstream and body fluids of the host is another effective mechanism of evasion.
- Cyst formation by Entamoeba and other amoeboid parasites

Last updated: 29 September 2000.