Cutaneous larva migrans is a creeping eruption, which arises due to infection by the filariform larva of the hookworm (Ancylostoma), or the dog tapeworm (Strongyloides). It is the most common skin condition to occur in travelers who have been in tropical or subtropical regions.
It is usually acquired by direct contact with the larva in fecally-contaminated soil or sand, as on tropical or subtropical beaches.
The contact may occur through any part of the body, because the larva contains protease enzymes, which break down skin proteins to give them access to the epidermis. They enter intact skin, infect the skin follicles or creep through minute breaks in the skin.
Helminth infestation is rife in warm tropical or subtropical areas. Thus, the geographical distribution of cutaneous larva migrans follows the south-east coast of North America, Africa and Asia where helminthiasis is endemic.
The Etiologic Agents
Worms that cause cutaneous larva migrans include:
A. braziliense – definitive hosts are dogs, cats
A. caninum – definitive hosts are dogs
Urcinaria stenocephala – definitive hosts are European dogs
Bunostoma phlebotomun – definitive hosts are cattle
S. pyoncyonis – definitive host is the raccoon
Gnathostoma spinergium – definitive hosts are cats, dogs
Loa-loa worm – produces Calabar swelling
Fasciola hepatica – during ectopic migration only
A. ceylanicum – definitive hosts are humans and other mammals
A. tubaeforme – definitive host is the cat
S. papillosus – definitive hosts are large and small cattle
S. westeri – definitive hosts are horses
Etiopathogenesis of Cutaneous larva migrans
Dogs and cats are infected with helminth larvae either by:
- vertical transmission of larvae between the mother and the nursing baby animal
- by ingesting infected animal meat
- by oral ingestion of fecally-contaminated food containing the worm eggs
This form of human helminth infection occurs in those who walk, sit or lie with bare skin exposed to soil or sand, which is contaminated by infected dog or cat feces. The host animals pass eggs into the soil, following which hatching occurs. The larvae undergo molting repeatedly, and transform into the filariform larvae.
These are able to penetrate the skin of humans, and travel through the epidermis. A papule or vesicle is often formed at the site of entry of the larvae. They move slowly or rapidly, from 1 cm per hour to 1 cm per day. They burrow through sub-epidermal tissue, leaving winding red raised indurated burrows, which eventually dry and crust. Besides the tortuous track, the key symptom is the severe itching that occurs immediately after the larva starts to move. The redness is well-defined.
Most Stronglyloides species produce the same rash as above. In the case of S. stercoralis, the track is less clear. The larva moves much faster, up to 10 cm per hour, producing a rapidly advancing line with a red flare around it. The rash lasts only a few hours. This reaction is therefore distinct from cutaneous larva migrans, and is designated larva currens, since it races rather than creeps.