yes people underestimate the survival ability of these parasites, as dormant eggs have been found in soil over a few thousand years old.
as far as i understand, parasites love to eat the solvents that your body creates. when a woman becomes pregnant the uterus is lined with a multitude of solvents to help prepare a safe place for the new child to grow, and these worms, sporozoa, flukes, etc, are attracted to the solvents to feast upon.