Cutaneous larva migrans

 

Salient features

 

·       Due to larvae of animal hookworms (intestinal nematodes)

 

·       Skin lesions are serpiginous and pruritic, representing the paths of migration of organisms within the epidermis

 

·       The rate of migration is 1–2 cm per day

 

·       Self-limited disease

Introduction

Cutaneous larva migrans is a serpiginous cutaneous eruption caused by the accidental penetration and migration of animal hookworm larvae through the epidermis. The prime features, as the name suggests, are that the lesions creep or migrate, and that they are due to the presence of moving parasites in the skin. The infection has a worldwide distribution and occurs most frequently in warmer climates. The skin lesions are usually self-limited.

 

Causative organisms

 

Cutaneous larva migrans is caused by the larvae of hookworms that infect domestic dogs and cats, most often Ancylostoma braziliense or A. caninum and occasionally Uncinaria stenocephala or Bunostomum phlebotomum.

Adult hookworms live in the intestines of dogs and cats, and their ova are deposited in the animals’ feces. Under favorable conditions of humidity and temperature, the ova hatch into infective larvae, which will penetrate human skin. The infection is usually acquired by walking barefoot on ground contaminated with animal feces, but the buttock or other body sites can become infected via contact with contaminated soil or sand. The larvae enter the skin and begin a prolonged process of migration within the epidermis. With rare exceptions, the parasite remains confined to the epidermis, producing visible tracts and intense pruritus. The parasite lacks collagenase, which is necessary to disrupt the basement membrane.

 

Clinical features

 

The larvae may cause a pruritic erythematous papule in a few hours at the point of entry where the skin has been in contact with infected soil. This is commonly the feet, hands and buttocks. They can then lie quiet for weeks or months, or immediately begin creeping activity with the production of a wandering thread‐like serpiginous “tracts”. Typically one to three such serpiginous lesions, 3 mm wide and up to 20 cm in length are present. This is exceedingly itchy, slightly raised, flesh‐colored or pink. In severe infections, hundreds of such lesions may be found on a single patient. The pathognomonic garland or zigzag-shaped inflammatory stripes becomes visible at the beginning of larval migration.

The larvae advance at a rate of a few millimeters to a few centimeters daily, and in some a blister is seen that marks the head of the tract. If untreated, a single larval tract may progress, then disappear for a few days, reappear, advance some more, and so on, for weeks or months, after which time it will spontaneously resolve. The wanderings of an individual larva are usually confined to a relatively small area, but exceptionally it travels much further. Due to intense pruritus and scratching, superimposed bacterial infections and dermatitis may complicate the clinical picture. In later stages, these tracks are difficult to see, the path being marked by small itchy nodules.

The disease is self‐limiting. Estimates for the natural duration of the disease vary considerably. This variation almost certainly depends on the species of larva observed, and this is usually unknown.

 

Larva migrans can be accompanied by Loeffler syndrome of pulmonary eosinophilia, particularly in severe infestations.

 

 

 

Differential diagnosis

 

The main differential diagnosis is the larva currens (‘running larva’) of strongyloidiasis. The main distinguishing factor between the two diseases is the speed at which the larvae travel. Larva currens is known for its distinct rapidity, with the larval track progressing at approximately 0.2 cm/min, with cutaneous lesions progressing up to 5–15 cm/h. In cutaneous larva migrans, the larval track progresses at approximately 1 cm/h with cutaneous lesions only progress a few millimeters to a few centimeters daily.

 

Diagnosis

 

The classic clinical picture of wandering, advancing, serpentine and itchy lesions is easily recognized, but may be atypical, hidden by vesicles and scaling, or spoiled by scratching and secondary infection.

Biopsy in larva migrans is of little value, as the larvae have advanced beyond the clinical lesions.

 

Treatment

Although cutaneous larva migrans is self-limited, its potential complications (e.g. impetigo and allergic reactions), together with the intense pruritus and the significant duration of the disease (sometimes several months), usually necessitate treatment.

Antihelminthic treatment is warranted to relieve symptoms and reduce the likelihood of secondary bacterial infection. Ivermenctin is the preferred treatment, and is given at 200 μg/kg PO × 1 or 2 days. Albendazole 400 mg/day PO to adults and children >2 years of age for 3 days is also effective, although in some cases the responses are poor.

Topical 10–15% thiabendazole solution may have benefit for localized disease, but it requires application three times daily for at least 15 days. This therapy leads to healing in 90% of cases. The local treatment must be carried out over a large area beyond the larval duct, as the larvae often sit in front of the visible duct.

Freezing the leading edge of the skin track (cryotherapy) has been suggested, but this modality is rarely sufficient. 

 

Therapeutic ladder

First line

·        Ivermectin 200 μg/kg orally once daily for 1 or 2 days

Second line

·        Albendazole 400 mg orally for 3 days