How mice survive infection by virulent Toxoplasma parasites

One of the commonest parasites in the world is Toxoplasma gondii. Toxoplasma can infect most warm-blooded animals, including humans, and causes significant damage to the unborn child if a woman becomes infected for the first time during pregnancy. The natural cycle of the organism depends on cats and on mice. Infection by Toxoplasma normally doesn't kill the animal, but there are some "virulent" strains that kill mice only a few days after infection.