In vitro culture of Toxoplasma gondii can provide tachyzoites which are active, viable and with desirable purity. Thus the aim of this study was to optimize the cell culture method for T. gondii propagation to obtain a consistent source of parasites with maximum yield and viability, but minimum host cell contamination for use in production of excretory-scretory antigen. Tachyzoites with seed counts of 1× 106, 1× 107 and 1× 108 harvested from infected mice were added to VERO cells of different degrees of confluence, namely 50%, 85% and 100%, and examined periodically using an inverted microscope. When the maximum release of the tachyzoites was observed from the host cells, the culture supernatant was removed and the tachyzoites harvested. Using a Neubauer chamber, the percentages of viable tachyzoites and host cell contamination were determined using trypan blue stain. Parameters that gave the best yield and purity of viable tachyzoites were found to be as follows: VERO cells at 85% confluence in DMEM medium and inoculum comprising 1× 107 tachyzoites. After about 3 days post infection, the tachyzoites multiplied 78×, with a yield of~ 7.8× 108 per flask, 99% viability and 3% host cell contamination. This study has successfully optimized the method of propagation of T. gondii tachyzoites in VERO cells which produce parasites with high yield, purity and viability.

Toxoplasma gondii is an obligate intracellular protozoan parasite. The RH strain can be easily grown in vivo and in vitro, and a culture system which can reliably provide tachyzoites of consistent high quality would greatly benefit studies on the live organism (Chatterton et al., 2002). The Sabin-Feldman dye test is the gold standard among serological tests for detection of T. gondii infection, it is also the most difficult test to maintain because of its requirement for viable tachyzoites, and this has been made possible by in vitro culture