Although most common parasites of people, like pinworms and head
lice, only infect people, some intestinal helminths (worms) of
dogs and cats can also occasionally infect people, especially
children. How this occurs depends on the species or type of
worm. The common dog and cat ascarids (commonly referred to as
roundworms), Toxocara canis and Toxocara cati, respectively,
pass eggs in the feces of an infected pet. These eggs develop to
the infectious form in the soil and can survive in the
environment within a thick-shelled egg for many years. When
these infective eggs are ingested by another dog or cat, the
adult worms develop in the intestine. However, when the eggs are
ingested by a child - usually because the child eats dirt from
an area contaminated with animal feces sometime in the past –
the larvae migrate in the tissues of that child, creating severe
inflammation. The larvae may go to the liver and cause damage
there (visceral larva migrans), or they can even go to the eye,
where a condition known as o