Background and study aim: There is a need for more detailed characterisation of T. gondii strains to determine the level of genetic variability which is useful in effective diagnosis, treatment and control of toxoplasmosis. This work aimed to assess the difference between the two sequences of Hsp60 gene of both RH and ME 49 strains of T. gondii and to investigate its role in the virulence of the parasite.
Materials and Methods: Two strains of T. gondii parasite RH and ME-49 were used for experimental infection of mice groups which were divided into group I (infected with RH strain), group II (infected with ME-49), and group III (non-infected non treated group).
Results: Histopathological examination showed that there was a statistically significant increase in the intensity of infection in liver and spleen of group I and in kidney and brain of group II, with no difference between both groups organs. Molecular and Bioinformatics studies included Primers design using primer 3 program, primer 2 (P2) was selected and used in PCR amplification according to its highest product size 247 bp. The results of Insilico PCR amplification program that was carried out to amplify Hsp60 gene theoretically using primer 2 (P2) showed higher number of positive samples that detected in group II than group I, there was significant statistical increase in frequency of brain infection in group II.
Conclusion: Our results showed that PCR was a highly sensitive, specific and rapid technique for detecting T. gondii. It revealed higher positive results in chronic strain (ME49) especially in brain tissue than acute strain (RH) but it may show false negative results in some samples. Both PCR technique and histopathological examination showed that the preferred tissue for detection of T. gondii in experimentally infected mice was liver & spleen in acute strain (RH) and brain & kidney in chronic strain (ME49).  Bioinformatic analysis of Hsp60 gene sequences of both (RH & ME 49) strains of T. gondii showed that there was a polymorphism in some nucleotides between the 2 sequences.