Assay for protection against oral challenge. Mice were nasally immunised with 30 μg rTgUPase or PBS. Two weeks after the last immunisation, mice were orally challenged with tachyzoites. (A) Mice from two groups (n = 8 PBS and 8 rTgUPase) were orally infected with 1 × 10⁴ tachyzoites of the T. gondii RH strain. Liver and brain tachyzoite burdens were evaluated one month after the challenge. (B) Mouse survival rates of the two groups (n = 12 PBS and 12 rTgUPase) were monitored daily after challenge with 4 × 10⁴ tachyzoites of the T. gondii RH strain until Day 30 post-challenge. Differences in survival were significant (p < 0.01). These results are representative of two independent experiments. Values are the means ± SDs. ** p < 0.01. PBS, phosphate buffered saline.