It’s not at all uncommon for strange skin conditions to be attributed to bugs, or bug bites. As an entomologist, it’s also not at all uncommon for someone to ask me to look at their weird skin condition, sometimes even when I really don’t want to.*
Today’s strange skin feature is Larva Migrans. Or, more technically, cutaneous larva migrans.
What’s going on? A parasitic worm has found a potential host! It’s tiny enough to burrow into your skin via a pore or a hair follicle, looking for a good home.
Check out the life cycle of some of these parasitic worms. If it’s a human hookworm, they burrow into your feet, travel in your blood stream to your lungs where you cough them up, swallow them, and then they finally reach their happy home in your intestine. Where they breed.
Larva Migrans is what happens when something goes wrong in that worm lifecycle.
Usually you see these marks on the skin when the worm that’s gotten into you isn’t one that’s supposed to live in people–dog hookworms are a common cause of Larva Migrans. These worms may not be able to penetrate the lower layers of human skin to get into the blood stream, so just wander around between the layers, looking for an opening. Hence the name: Larva Migrans, or wandering larva.
What are the risk factors for Larva Migrans?
- Hobbies and occupations that involve contact with warm, moist, sandy soil
- Tropical/subtropical climate travel
- Barefoot beachgoers/sunbathers
- Farmers and Gardeners (Ahem.)
Fortunately, while it looks gross, and the concept usually squicks people, it’s usually harmless and self-limiting. The larva dies, and the problem is solved after some severe itching and mild freaking out.
The worms that most commonly cause LM are found in damp, humid areas, or moist soils. The free-living stage of the worm is very tiny, so they need a wet environment to keep from dehydrating. Tropical jungles and swampy land tend to be a very nice place for these worms to live.
The other thing these worms need is for a currently infected animal to poop someplace near that moist soil or sand, so that the eggs and juvenile worms can find a new host. Like your foot.
So, Larva Migrans is mostly limited to those who live in or visit developing countries where sanitation is lacking, or natural areas and farms where infected animals’ feces are deposited at will.
And where bare skin comes in contact with said soils or feces. When mom yelled at you to put your shoes on, she was onto something.
It’s pretty rare, especially for those of us up here in the frozen north, but I thought you would like something new to be paranoid about.
*I had a guy try to drop trou in my office once so he could show me the bites on his derrière. Fortunately my boss was there, and made the guy put his pants back on.