Ask an Entomologist: Larva Migrans

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.

foot with larva migrans

This condition is NOT caused by an insect, but by a round worm, or more properly, a nematode. This is a photo of the bottom of someone’s foot, a common spot for the condition to occur.

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.
Yum.

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.

11 thoughts on “Ask an Entomologist: Larva Migrans

  1. We had a woman come into the museum once with a botfly larva in a jar. When asked where she had gotten it, she stammered for a moment and said “Out of my fatty tissue. I think there’s another one. Here, let me show you…” We had her keep her clothes on and see her physician. We still refer to her as Botfly Lady.

  2. Fortunately, some of us know the difference between a medical doctor, and a PhD of other disciplines. I’d hate to be the classicist asked to compare an affliction to Philoctetes.

  3. I knew there were even more reasons than I knew to wear chest waders while collecting field data for 2 summers in a Carolona Bay, ie. swamp.

  4. Working with pigs and chickens I get rather more exposure to parasites than is reasonable for non-bug people. Fortunately, I find them rather interesting—much to the disquiet of people who don’t.

    Anyone for Ascaris Suum?

  5. Parasites are fascinating! Although watch out for Ascaris, they’re quite nasty, and humans can get them (although rare).

    I really liked teaching parasitology. :)

  6. Most likely I’m posting this in the wrong place or in the wrong way so appologies in advance but I couldn’t seem to find the right place (what else is new?).

    The reason for my post is that I’ve lived in S. Calif. for many years and I recently observed an insect that I’ve never seen before. I thought at first that it was a baby hummingbird as it was gathering nectar from the flowers in my planter.

    It was approximately 2.0″ long with a triangular shaped body, antennae and a long probiscus that it was using to gather nectar. It also hovered in place much like a hummingbird

    Possibly this insect is common to S. Calif. and I’ve just been oblivious (which is also something that isn’t new). However, I’m fairly certain I’ve never seen one before.

    I’m wondering if you can identify it. I took a few photos if that will help.

    Jeff T

  7. thanks for the LARVA MIGRANS INFO – BEEN DEALING WITH THIS FOR MONTHS MYSELF WITH DR.S WHO REFUSE TO TREAT ME SO I HAVE HAD TO MAKE FRIENDS WITH MY PARASITIC MIGRANS. IT IS PAINFUL AS THEY TRAVEL IN MY MUSCLE TISSUE – SOME HAVE DIED BUT I DO BELIEVE I AM HEAVILY INFESTED … THEY HAVE MADE IT TO MUSCLE TISSUE IN THE EYE AREA AND THAT IS NOT ONLY SCARY BUT VERY PAINFUL AS THEY DIE AND COME OUT OF MY NOSE AND EYE DUCTS… HELP! DOES ANYONE HAVE ACCESS TO IVERMECTIN PASTE?

  8. First, using all capitals online is very rude. It’s considered shouting.

    Second, the definition of larva migrans is that they do NOT penetrate into deeper tissues.

    You may very well have a condition that makes you believe that you have things coming out your eyes and nose. But it isn’t parasitic.

    Your doctors probably have offered you some medication for pain, and probably also suggested a psychological or neurophysiology evaluation. Try that first, before dosing yourself with medication that won’t help, and may make things much worse.

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