The larvae of some nematodes penetrate transcutaneously and give rise to the classic dermatosis called "larva migrans cutanea" or, as it was described in England by Lee, "creeping eruption."
These nematodes, also called roundworms, usually infest some animal species and are:
- Ancylostoma brasiliense, a parasite of dogs, cats and wild animals. It is endemic in parts of Central and South America, but also in warm humid climate zones on other continents;
- Ancylostoma caninum, a parasite of the dog, which, having difficulty penetrating, can give a typical detected, serpiginous urticarial reaction;
- Necator americanus, is responsible for a strongly itchy urticarial rash similar to the parasite Ancylostoma caninum.
Penetration occurs typically in the back of the foot (not the sole, which is strongly resistant) and in the interdigital spaces, more rarely in the hands, knees, and buttocks.
Initially the sting is felt, not always detected by visual examination, followed later by erythema and itchy papule, marking the first stage of nematode migration.
The main feature is the serpiginous, relatively inflamed lesion. We can identify in the pathway of the parasite a head zone, with papular-vesicular or erythematous-vesicular appearance, and a tail zone, characterized by increased pigmentation and scaling. But among all of them, the most recognizable symptom is extremely intense itching.
It should be pointed out that the lesion is usually located in the epidermis: the parasites do not have enzymes capable of attacking the basement membrane, preventing them from penetrating into the superficial dermis.
The death of the larvae normally occurs after a period of 14 to 56 days, but given the nature of the symptoms and the risk of bacterial infection, treatment may be necessary.
Treatment generally consists of topical thiabendazole, particularly in galenic form, albendazole or ivermectin. Some dermatologists alternatively use cryotherapy, with the application of liquid nitrogen to the head area of the tunnel created by the advancement of the parasite.