Visceral Larva Migrans

Visceral larva migrans are what happens when human organs are invaded by nematode larva. Toxocara canis (typically found in dogs) and Toxocara cati (cats) are the most common forms of this infection. The eggs are passed out of the body of the host in feces, and are then ingested. When they accidentally get into humans, they hatch in the small intestine, and then permeate the intestinal mucosa, from which they migrate through the blood and lymph systems to the major organs, such as liver and lungs. This problem is rarely fatal, and is indeed very often asymptomatic. Unless one gets into somewhere really bad, it may only present as slightly high levels of eosiniphils in the blood, which can also be caused by allergies or asthma. Problems can occur, however, when a larva invades the eye. This can look like a retinoblastoma. Since the cure for retinoblastomas is removing the eye, and the cure for visceral larva migrans is a simple course of anti-helminthics (and possibly surgical removal of the larva), this can be an important distinction to make! One clue is that this typically presents in older kids than those commonly infected with retinoblastomas. Just something to look out for!




A MUCH larger problem can occur when the visceral larva migrans are due to Baylisascaris procyonis. These helminths are found in the intestinal system of raccoons. They have become more of a problem lately, as raccoons are moving closer and closer into where people live. They are an ascarid-type nematod (remember Ascaris lumbracoides, the intestinal roundworm!). They need to live in raccoon feces in the soil for around one month before they are infectious. Seems pretty easy to avoid raccoon feces, right? The problem is, raccoons like to have one spot that they designate the "toilet", traditionally in the crook of tree branches. As raccoons are moving closer to humans, they are more and more frequently building their "toilets" on top of buildings, which causes the feces to get swept down to the ground when it rains. Since the majority of the debris will be washed away, it can be difficult to tell where eggs might be! Once the Baylisascaris larva are ingested, they really go crazy. They go straight to the eggs and the brain. Unlike most other lost baby worms, these actually do grow up to adults - in your brain. This causes both an eosiniphilic allergic reaction (meningitis) AND severe brain damage, as you now have a worm carving tunnels in your brain. Unfortunately, the only real prevention for this one is washing your hands if you think you've been anywhere near a raccoon toilet.

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