KINETICS IN PARASITE ABUNDANCE IN SUSCEPTIBLE AND RESISTANT MICE INFECTED WITH AN AVIRULENT STRAIN OF TOXOPLASMA-GONDII BY USING QUANTITATIVE COMPETITIVE PCR

The kinetics of changes in Toxoplasma gondii abundance were evaluated with a quantitative competitive (QC)-polymerase chain reaction (PCR) a ssay at various sites in both C57BL/6 and BALB/c mice. Higher mortalit y was apparent in C57BL/6 mice than in BALB/c mice when infected with a high dose of cysts. There were significant differences in cyst numbe r when infected with a low dose of cysts, although there was no signif icant difference in mortality between the 2 mouse strains. One day aft er infection with a low dose of an avirulent Fukaya strain, T. gondii was detected in peripheral blood, mesenteric lymph nodes, spleen, lung s, and brain. Two weeks after infection, the number of T. gondii in th e brain greatly increased in C57BL/6 mice but not in BALB/c mice. Thus , it would appear that the first to second week after infection is a c ritical period in determining T. gondii abundance. QC PCR allows the d etection of low numbers of T. gondii at an early stage of infection in the murine model. This is useful for the early diagnosis of toxoplasm osis and to understand reactivation of toxoplasmosis.