Study of Genetic Polymorphism of Toxoplasma Gondii Through Isoenzyme Analysis

Abstract

Genetic polymorphism is a well-known phenomenon in protozoan species. It has been studied for many years in Leishmania sp., Entamoeba histolytica, Trypanosoma sp., and Plasmodium falciparum. Toxoplasma gondii is one of the last medically important protozoa to be studied. Several aspects of T. gondii epidemiology and biology strongly suggested genetic diversity. This parasite has a wide geographical distribution and a considerable host range. Furthermore, differences in parasite behaviour within the same host species could indicate that the species T. gondii may be composed of heterogeneous populations. Based on pathogenicity in Swiss mice, 3 main groups of isolates are generally recognised: acute isolates which kill the mice in 5 to 10 days, chronic or non-pathogenic isolates, and subacute isolates killing the mice within a few weeks or months. Similarly, human toxoplasmosis exhibits a wide range of clinical manifestations which can not entirely be explained by the immune status of the host. Nevertheless, because of the influence of host or environmental factors on extrinsic characteristics, there is no certainty that such variability reflects genetic differences between strains.