It's like something out of the movie Aliens, but it's science, not fiction. Larval parasites can
be transmitted to humans, where they can "migrate"-or move-from the intestine to the eye,
brain, or other internal organs, possibly causing organ damage, blindness, and in rare
instances even death. Luckily, only a very small number of people get these symptoms, and
you can take steps to reduce the risks for your pet and for you.

"Toxocara canis is one of the most common intestinal parasites of dogs. This type of worm
is one of a group known as ascarids," says Dr. Allan Paul, small animal Extension
veterinarian at the University of Illinois College of Veterinary Medicine in Urbana.

"Almost every puppy is born with this parasite. Every puppy should be dewormed at 2, 4,
6, and 8 weeks of age. The mother and her pups should be dewormed at the same time,"
explains Dr. Paul. Kittens should be dewormed at 6, 8, and 10 weeks. Kittens, unlike
puppies, are not infected before birth but rather obtain the infection through their mother's
milk.

Puppies get the infection before birth through the placenta and after birth via the mother's
milk. Even if the mother has been dewormed, larvae encapsulated in her liver, skeletal
muscle, and kidneys are not killed. At day 42 in the dog's pregnancy, these larvae "wake
up" and migrate through the placenta and umbilical vein to the fetal liver. Late in the
pregnancy larvae move to the mammary glands, and by the fifth day of nursing they infect
the milk. Eggs are passed in the puppy's feces about 3 weeks after birth. Two weeks later
the egg of Toxcara canis may be capable of infecting humans.

Infected puppies typically have a rough coat, pot bellies, bad breath, general failure to
thrive, and sometimes vomiting and diarrhea. "Migrating larvae may carry bacteria into the
intestinal wall, the circulatory system, and other organs through which they move. They can
also cause meningitis, encephalitis, and other central nervous system disorders," says Dr.
Paul.

If two-week-old eggs are somehow ingested by humans (typically by young children who
eat dirt), the eggs hatch and larvae may migrate through organs or to the eye or central
nervous system. Such migration may cause organ damage, blindness, or, if the central
nervous system is involved, death. These cases are very rare. One estimate indicates that
about 2.8% of people in the United States test positive for Toxocara infection. The vast
majority of these, however, do not experience symptoms or problems.

Wildlife can also harbor and distribute the infective stages of migratory parasites. "Hygienic
measures, such as thorough hand washing, should especially be taken when working where
raccoons have been," says Dr. Paul. Raccoons like to defecate on wood piles. Cases have
been reported of children being infected by sucking on wood chips from an outdoor wood
pile.

Several types of hookworms migrate in humans as well. People are infected when larvae
penetrate their skin. "The main problem of hookworm infections in your pet is blood loss.
Because the hookworms damage the lining of the intestine when they suck blood, bacterial
infections may arise at feeding sites," says Dr. Paul.

In humans, a type of hookworm called Ancyclostoma can cause cutaneous larva migrans,
also known as "plumber's itch." The disease is described as a creeping eruption, i.e., a trail
of the larval migration in your skin. "Electricians, plumbers and other workers who crawl
beneath raised buildings, sunbathers who recline on wet sand, and children typically
become infected," according to the Centers for Disease Control and Prevention (CDC).

A publication from the CDC that urges veterinarians to educate pet owners about intestinal
parasites notes: "In the United States, the popularity of pets together with high ascarid and
hookworm infection rates in dogs and cats, especially pups and kittens, result in widespread
contamination of soil with infective-stage larvae." Children's play habits and attraction to
pets put them at risk for parasite infection.

The best way to prevent ascarid and hookworm infection in you and your pet is to deworm
pets, especially young pups and kittens and their mothers. These animals harbor large
numbers of the parasites at an infective stage. To prevent contaminating the environment,
always pick up your pet's feces whether your animal is infected or not. Do not allow
children to play in areas where infected pets or wildlife may have been.