A study of virulence parameters for Toxoplasma gondii infections in mice

With the aim of establishing assessments of the virulence of Toxoplasma gondii isolates for mice, we investigated weight loss, serum levels of haptoglobin, and serum levels of tumor necrosis factor-alpha (TNF-alpha) as alternative parameters to mouse mortality. Groups of BALB/c mice were inoculated i.p. with increasing parasite doses (5 x 10(1), 10(4), and 10(6)) of isolate 119 and with a low dose (5 x 10(1)) of isolates GT1 and NED. The inoculation dose was inversely correlated with the interval to the onset of weight loss (starting at days 9, 7, and 5, respectively) and the onset of increase in serum haptoglobin (starting at about days 8, 6, and 4, respectively). The GT1 strain (inducing 100% mortality at day 9) also gave the fastest response in terms of weight loss (onset by day 8) and increase in serum haptoglobin (onset by day 6), which occurred 1-2 days before these parameters were affected in the other low-dose groups. The low-dose NED and 119 inoculations were distinguished by continued weight loss, which lasted until day 20 in the former group (max. average weight loss 2.9 g as compared with 0.4 g).