Cutaneous Larva Migrans Infection in the Pediatric Foot. A Review and Two Case Reports

Abstract

Cutaneous larva migrans is the result of infestation of human skin by helminth larvae, which burrow through the epidermis. This route of infestation makes the foot a typical site for origination of this infection. Children, who frequently play barefoot in locations where the most common of the helminth larvae, the dog and cat hookworms, are endemic, are at particular risk for this disorder. This article reviews the differential diagnosis of cutaneous larva migrans and current concepts in management. Two cases of related children who presented to their pediatricians with this condition are reported. (J Am Podiatr Med Assoc 88(5): 228-231, 1998)

Cutaneous larva migrans results from the infestation of the skin by helminth larvae, most frequently the dog and cat hookworms Ancylostoma caninum and Ancylostoma braziliensis [1]. The adult worms release eggs while in the intestines of their definitive hosts, dogs and cats. These eggs are passed with stool onto sandy, warm soil, which serves as a rich incubator. The eggs feed on soil bacteria and mature into noninfectious rhabdiform larvae and subsequently into infectious filariform larvae [2].

As often happens on beaches, the infectious larvae encounter accidental hosts such as humans and penetrate the epidermis of intact skin by means of proteases. The larvae can also enter through broken skin or hair follicles. At this stage patients report a “tingling” or “prickling” sensation. Reddish brown, pruritic papules erupt at this site several hours later [3]. After entering the epidermis, the larvae are unable to penetrate the dermis and commence a process of wandering through the skin. This migration, from the time of penetration to the onset of symptoms, can vary in length from days to weeks. In a recent review, the mean period of time between exposure and penetration and the onset of symptoms was 2 to 50 days [3]. The tunneling of the parasites under the epidermis creates sharply demarcated, extremely pruritic linear or serpiginous tracks. The larval burrows advance from a few millimeters to a few centimeters a day. Interestingly, the larvae are 1 to 2 cm ahead of the track, and vesicles may form in the track as the worm changes direction. These vesicles become thick and encrusted, possibly resulting in scarring [4]. Secondary bacterial infection has been documented as the most common complication.

Given the mode of penetration of the host, it is not surprising that the areas most frequently affected are the dorsal and plantar aspects of the feet and interdigital spaces between the toes [1]. Other areas, less frequently affected, include the arms and the breasts. In occupational exposures, the hands are more commonly involved in the cases of animal handlers and gardeners [5], and the legs in house painters [3]. The larvae have been shown to penetrate thin clothing such as bathing suits, and the buttocks are another area of eruption, especially in young children.

Infestation by the larvae forms has been documented in the southeastern United States (most commonly Florida and Georgia), the Caribbean, South America, Mexico, tropical Africa, India, and southeastern Asia [3]. In a recent review of 60 cases presenting to the Tropical Disease Unit of the Toronto Hospital in Ontario, Canada, 48% of the patients had traveled to Jamaica [1]. An analysis of the areas where dog and cat hookworms are endemic would demonstrate the importance of always obtaining a travel history as well as a history of visiting beaches, being near uncovered sandboxes, or involvement in an occupation conducive to exposure.

The differential diagnosis includes other helminth larvae such as Strongyloides stercoralis. Its eruption usually occurs in the perianal area because the worm is deposited there by the stool of its human host. This helminth moves much more rapidly (5 to 10 cm per day) than the dog hookworm and is thus aptly termed “larva currens,” meaning larva that runs or races [1]. Other helminths may manifest similar early symptoms. These include the human hookworms Necatur americanus and Ancylostoma duodenale, which cause a condition known as “ground itch.” This term denotes the creeping eruption usually found at the site of entry, the foot; it has an appearance similar to that of cutaneous larva migrans. Unlike the dog and cat hookworms, however, this organism is able to complete its life cycle in the human, its primary host. The eruption lasts about 2 weeks, after which the larvae penetrate the dermis and complete their development in the human gut [6]. The last parasite in the differential diagnosis is Gnathostoma hispidum, suborder Spirurina. This infestation is common in Japan as the result of ingestion of raw loach fish or other freshwater fish; it causes a prolonged eruption lasting as long as 3 years. The eruption has a distinctive shape and size, being narrower and longer than that of cutaneous larva migrans, presumably because of the parasite’s morphology [7].

The differential diagnosis would not be complete if it did not include nonhelminthic diseases that can mimic symptoms of cutaneous larva migrans. Two such conditions are scabies and linear lichen planus. Classically, scabies infestation involves the hands, and accurate diagnosis is not difficult. However, when it occurs between the toes or has an atypical efflorescence on the hands, a diagnostic challenge may present itself [5]. Typical features of scabies should be considered, including a history of exposure, crustaceous papules, and a microscopic demonstration of the scabies mite or its feces. Scabies also features multiple lesions, in contrast to cutaneous larva migrans, which usually is present at only one site [2].

Lichen planus is a pruritic eruption frequently seen in children. Although the characteristic lesion is a shiny, flat-topped papule, it occasionally occurs as a linear eruption. Other distinguishing features include its nail involvement, histopathology of a hyperkeratotic stratum corneum, and its good clinical response to topical corticosteroids [8,9].

Therapy for cutaneous larva migrans has traditionally included two unsuccessful approaches. Cryotherapy with liquid nitrogen has caused pain and blistering around the area of infestation without producing remission or cure [1]. The ineffectiveness of this treatment is due in large part to the fact that the larvae have already passed through the tissue and are several centimeters ahead of the inflammation. Therefore, application of caustic substances to the area of inflammation serves only to further irritate the site. Moreover, the larvae have been shown to be capable of withstanding temperatures as low as −21°C for more than 5 minutes. The advanced position of the larvae as compared with the inflammation also makes the second approach, surgery for excision or biopsy, futile [10]. Pathologic specimens demonstrate an eosinophilic inflammatory response but no organism.

Current recommendations for the treatment of cutaneous larva migrans include oral thiabendazole, 25 mg/kg/day divided into two doses, with a maximum of 3 g/day. Treatment length varies from 2 to 5 days. If treatment failure is seen after 2 days, the drug may be continued for another 2 days. Frequent side effects of this drug consist mainly of headache, dizziness, and gastrointestinal disturbances. Although rare, serious secondary effects such as seizures, erythema multiforme, and toxic epidermal necrolysis have been reported [11]. A better-tolerated therapy is topical thiabendazole as a 10% or 15% aqueous suspension. Applied four times a day for 10 days, this treatment is highly successful, with a cure rate of up to 98% [10]. Side effects include minimal burning at the site of inflammation.

Newer alternatives to thiabendazole include albendazole and ivermectin. Albendazole is given orally at 400 mg/day for 3 days or 200 mg twice daily for 5 days. Because of this drug’s absence of side effects, it has become a treatment of choice in some instances. Rare adverse effects include abnormal liver function, neutropenia, and fever [11]. Although the failure rate in some studies is low [11], other investigations demonstrate a failure rate of nearly 50% [12]. The antiparasitic drug ivermectin is currently under study; it is given in a single dose of 200 mg/kg and has few side effects. It has been shown to halt the progress of this nematode within 48 hours [10].

Case 1

A 6-year-old boy presented to his pediatrician within 1 week of his return from a trip to Jamaica. The patient initially complained of several “mosquito bites” on the sole of his foot on the fourth day after his return. When topical steroids were only moderately successful in relieving the pruritus and did not stop the progression of the condition, the patient’s parents sought medical advice. By the day of his examination, the lesions had begun to form a serpiginous, extremely pruritic track creeping up the medial aspect of his right foot. Pruritus was described as intense enough to awaken the patient from sleep several times during the night. A diagnosis of cutaneous larva migrans was made and the patient was subsequently treated with oral thiabendazole for 5 days. The pruritus resolved within 48 hours of beginning treatment; however, the patient experienced several episodes of dizziness and nausea while being treated with oral thiabendazole.

Case 2

An 8-year-old boy presented to his pediatrician 2 weeks after returning from a trip to Jamaica. He had a history of an enlarging pruritic track over the plantar aspect of his left foot that began about 10 days after his return. The patient’s cousin (Case 1), who was on the same trip, had been diagnosed with cutaneous larva migrans the week before. Despite this diagnosis, this patient’s pediatrician, unsure of the correct diagnosis, referred him to an infectious-disease specialist. The patient was subsequently treated with oral thiabendazole for presumptive cutaneous larva migrans but was able to complete only 3 days of his 5-day treatment regimen owing to side effects. The patient continued to have occasional pruritus that resolved over the course of the following month.

Discussion

Knowledge of the life cycle of the dog and cat hookworms and the clinical manifestations of their infestation of human skin is essential to instituting prompt and efficacious treatment. Children are often the accidental host, and because they are usually unable to give the practitioner complete historical data, parental input is imperative. A complete history should include review of travel to a beach within 2 months of the onset of symptoms. The historical review should concentrate on the initial presentation of symptoms and pattern of rash, the course of the symptoms, the location of the lesions, any previous attempts at treatment, and whether any other family members are affected. Treatment is successful in most cases, but misdiagnosis and mistreatment often prolong the patient’s course. Treatment may consist of either oral or topical antiparasitic agents.

Without a comprehensive history from the child’s parents, it is impossible to perform a proper differential diagnosis including cutaneous larva migrans. In a recent review of 60 patients who presented to the Tropical Disease Unit of the Toronto Hospital with cutaneous larva migrans, 58% had already been misdiagnosed and mistakenly treated with a variety of therapies. These included oral antibiotics, acyclovir, antifungal and steroid ointments, and liquid nitrogen [1]. In Case 2, treatment was not immediately instituted despite knowledge of the cousin’s diagnosis, the patient’s classic symptoms, a history of frequenting beaches where dogs were common, a history of travel to the Caribbean (where the hookworm is endemic), and the typical location of the lesion. Aside from prolonging pruritus, misdiagnosis may result in the additional problems of pain and secondary bacterial infection.

Once a differential diagnosis has been formulated and various entities have been ruled out, a treatment plan should be promptly instituted. The difficulties of treating children with oral medication—which may be exacerbated by side effects, as occurred in Case 2—make topical thiabendazole the preferred therapy for pediatric cases. A significant infestation may require oral thiabendazole or albendazole.

Conclusion

The clinician must be aware that the geographic mobility of his or her patient population expands the list of possible skin conditions or infestations to include parasitic infections. Tropical diseases are frequently acquired during vacations, and clues to the diagnosis often lie within the patient’s history of travel and exposure as well as the typical examination findings. Although classic signs and symptoms such as intense itching and linear erythematous tracks may be present, the clinician must also consider the diseases that can mimic cutaneous larva migrans. Similarly, in children with a history of recent travel to endemic areas, any unusual rashes on the hands and feet demand inclusion of cutaneous larva migrans in the differential diagnosis.

In children, the longer (10 days) and more frequent (four times per day) administration of topical thiabendazole is preferred over the short (2- to 5- day) course of oral thiabendazole or albendazole. If topical treatment fails in children, oral treatment is usually required. The newer drug ivermectin has yet to be approved for use in the United States, although its one-time, single dosing would make it an excellent choice for patients of all ages once safety and efficacy are proven.