Answers

Short answers

1 Cutaneous larva migrans is a common, tropically acquired dermatosis caused by the percutaneous penetration and migration of larvae of nematode parasites.

2 Other infestations—including erythema migrans of Lyme disease, migratory myiasis, and larva currens caused by Strongyloides stercoralis—should be considered.

3 Cutaneous larva migrans is self limiting, but its clinical course is shortened by effective treatment with topical and oral anthelmintics such as albendazole, thiabendazole, and ivermectin.

Long answers
Cutaneous larva migrans is one of the most common imported parasitic infestations diagnosed in travel clinics¹ and to be considered in the returned traveller.^{2 3} It is a parasitic skin infection caused by hookworm larvae which parasitise cats and dogs but may also penetrate into the epidermis of humans.⁴ It is most commonly, but not exclusively, found in the tropical and subtropical areas as well as the southwestern United States, and is usually associated with outdoor activities that include exposure to contaminated water or soil in such areas.

In Brazil, cutaneous larva migrans is highly endemic in resource poor communities: in Fortaleza, a capital city in the northeast, a 2003 study reported a prevalence of 3%,⁵ and a further study showed that less than 1% of travellers to northeast Brazil acquired cutaneous larva migrans during an average two week stay.⁶

Many different species of hookworm may cause cutaneous larva migrans, the commonest of which are listed in the box. The lifecycle of the parasite starts when eggs are passed from infected animal faeces into warm water or moist soil, where the larvae hatch. The larvae use various proteolytic enzymes to penetrate the stratum corneum before migrating. In human hosts, the larvae lack the collagenase enzymes required to traverse the basement membrane into the dermis, so the infection is confined to the skin in humans (other animal hosts have systemic manifestations).

Cutaneous larva migrans often starts as a tingling or pricking sensation at the site of penetration, usually within 30 minutes of the larva breaching the skin. As the larvae migrate they cause a highly pruritic, advancing, serpiginous eruption. The lesion is erythematous, 2-3 mm wide, and often palpable, extending at a rate of 1-2 cm per day. For this reason it is also known as the creeping eruption. Oedematous papules and vesicles may be additional features, and secondary staphylococcal or streptococcal infection can complicate this parasitic infection. Lesions typically affect the feet and toes, but also the anogenital region, buttocks, breasts, hands, and knees—any area of skin likely to be in contact with contaminated sand. Systemic features, although not common, include peripheral eosinophilia, migratory pulmonary infiltrates, and raised concentrations of IgE.⁷

The diagnosis is based on the appearance of the rash and relevant travel history (the rash is often seen in patients who have been lying, sitting, or walking on a beach). A skin biopsy is not usually necessary but may show a superficial, eosinophil rich, chronic inflammatory infiltrate with spongiosis and necrotic keratinocytes. Larvae positive on periodic acid Schiff (PAS) staining can be seen on skin biopsy.

The condition is benign and self limiting. As human hosts do not support the lifecycle of the parasite, the larvae eventually die and the rash resolves within 4-8 weeks without treatment, depending on the species. The condition is highly treatable with anthelmintics, which shorten the course of the disease and relieve symptoms. The treatment of choice in localised disease is topical thiabendazole (15% in a hygroscopic base) for five days.⁸ Oral albendazole 400 mg a day for three days or thiabendazole or ivermectin 200 µg/kg in a single dose are used when topical treatment fails or in more florid cases. The prognosis is good, and with treatment the lesions resolve within a week or two.

Measures to prevent cutaneous larva migrans infection are also relevant, and travellers should be aware of the condition. Avoiding direct contact with sand is especially important, particularly in areas protected from tidal movement or intense sunlight, where the larvae are most likely to survive.⁷

Cite this as: BMJ 2009;338:b1451