Abstract: AIM: To investigate the pathogenic mechanisms of Toxoplasma strains
with different virulence. METHODS: Tachyzoites from 3 strains, Viz.RH, B 36 and
Fukaya strains, were challenged to in vitro cultivated Vero cells. Systematic
examinations on the earliest invasion time, the invasion rate and intracellular
multiplication were performed under different cultivation conditions. RESULTS: The
tachyzoites of all the 3 strains invaded the host cells wi thin a short period
after inoculation. Invasion rates were all increased along with the prolonged duration of infection. The intracellular multiplication was found to be most active in RH strain, moderate in B36, and comparatively slow in Fukaya strain s. Using purified tachyzoites freed from host debris and proteins and adding sufficient FCS in the medium may facilitate the invasion and subsequent multiplication of the parasite. CONCLUSION: Strain differences in pathogenicity to the host may be correlated to the genetically predetermined multiplication capabilities of the parasites after being invaded to the host cell, and that environmental factors may give certain impact on the invasibility of the parasite.

Key words: Toxoplasma, Vero cells, pathogenicity, invasion, multiplication