Immune responses to protozoan parasites and its relevance to diagnosis in immunocompromised patients

The parasitology includes different parasites, of which some are very severe, which have a development in the blood, inside the cells and visible after coloration (Plasmodium, Babesia, Leishmania, Toxoplasma) or mobiles, outside the cells (Trypanosoma, microfilariae). The diagnosis of these parasites is the first aim of the biological technics. Direct diagnosis, under the microscope, allows to identifie the parasite, its stage of development, and the parasitaemia, which is essential to the prognosis and the therapeutic outcome.The technics include the direct examination to identify the extra cellular parasites, which are mobile among the blood red cells, or thin and thick smear, after coloration. It is often useful to use other technics, such as filtration, culture or animal inoculation. Recently, the molecular biology increased the sensitivity and the specificity of classical methods. Such progress, available by some laboratories, must be adapted to the methods of emergency and low cost diagnosis. In some cases of pauciparasitism or retrospective diagnosis, serological methods are useful to detect the trail of parasites by circulating antigens or antibodies.