[Giardia-host relationship: variation of infection pattern]

In man, as well as in many species of vertebrates there exist several populations of Giardia duodenalis group which, though morphologically indistinguishable, show different level of heterogenicity in several characteristics, a.o. in surface antigens, isoenzyme make-up, RFLP, invasiveness for different hosts or pattern of experimental infection. Also the clinical observations in man distinctly suggested that G. intestinalis comprises several different populations. In the course of giardiasis apparent variability in clinical manifestations can be observed. In many patients the infection is symptomless and resolves spontaneously and in some others--variable intensity of symptoms is observed. Most likely both the parasite's characteristics and the host's feature will determine the clinical character of infection. It is well known that in some cases it is the host that responsible for the symptoms of the infection. Thus, for instance, clinical giardiasis links with immunodeficiency, malnutrition or young age. There are also evidences that some Giardia isolates have enhanced potency to provoke the disease of the host. It is considered that the variable pattern of the infection may be related to three different factors in host-parasite relationship: extra- and intrapopulation variability of Giardia isolates, the microenvironmental factors of the host's intestine, and the variable immune response of the host. The author describes data on the two first factors.