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Disease

The manifestations of zoonotic hookworm infection are the result of inflammatory reaction to the migrating larvae in the skin or, less commonly, migration in deeper tissues such as lungs, intestinal tract, or possibly the eye. In definitive host infections, larvae can enter the tissues but, in humans, the larvae of most species of animal hookworm cannot penetrate beyond the dermis. The larvae of A. braziliense will migrate in the epidermis and cause CLM for several weeks before dying, after which lesions on the skin resolve spontaneously. A. caninum and A. ceylanicum larvae can penetrate more deeply and have been associated with other clinical syndromes including eosinophilic enteritis. Eosinophilic pneumonitis has been reported to occur in patients with CLM, possibly due to deeper larval penetration involving the lungs. Allergic reactions may occur in multiply-exposed individuals with extreme inflammatory response around the exposed area of the skin.

Cutaneous larva migrans (CLM) in a patient’s foot over the course of one week. Photos courtesy of Florida Department of Health, Duval County Epidemiology

The incubation period for CLM is typically short, with signs and symptoms developing several days after larval penetration of the skin. However, in some cases onset of disease may be delayed for weeks to months. The median time to symptom development in reported outbreaks of CLM ranged from 10 to 15 days. The most common symptom is intense pruritis, which usually develops first, followed by the appearance of an irregular raised track with erythema, presumably marking the progress of the larva from the site of penetration. The track may move in the skin over time, but it is important to note that the location of the track does not necessarily relate to the location of the larva which is randomly moving ahead of the track formation. Typically, the track moves several millimeters per day and is about 3 mm wide. Single tracks or multiple tracks may be present, depending on the severity of infection. CLM is usually found in parts of the body that have had unprotected contact with contaminated soil or sand, often bare feet or skin not covered by clothing. Complications may develop such as vesiculobullous lesions and edema or, rarely, folliculitis. Eosinophilia may or may be present and is more likely when deeper tissue penetration occurs. Less common disease manifestions include eosinophilic enteritis, ocular larva migrans and diffuse unilateral subacute retinitis (DUSN). Rarely, eosinophilic enteritis has been associated with Ancylostoma caninum infections, probably due to deeper migration of larvae or possibly inadvertent consumption of infective larvae. Cases of ocular larva migrans have been attributed to zoonotic hookworm larvae migration to the eye, based on the smaller size of these larvae relative to Toxocara or Baylisascaris larvae. Zoonotic hookworm larvae migration has been suggested as a cause of DUSN, largely based on epidemiological features.

Diagnosis

CLM is a clinical diagnosis based on the presence of the characteristic signs and symptoms and exposure history. For example, the diagnosis can be made based on presence of raised erythematous tracks with pruritis on the feet or lower extremities of a patient with recent travel history to tropical areas. There is no serological testing for zoonotic hookworm infection and skin biopsy is not sufficiently sensitive to diagnose CLM since the location of the migrating larva cannot be predicted by the track. Differential diagnoses include hookworm, gnathostomiasis, and strongyloidiasis. Other conditions such as cutaneous pili migrans, myiasis, and scabies should also be considered.

Treatment

Since the zoonotic hookworm larvae usually will die after 5 – 6 weeks in the human host, the course of CLM is considered self-limiting. Some reports have described delayed onset and persistent clinical diseases. Treatment may be indicated to help control symptoms and to resolve secondary bacterial infections. Various treatment modalities have been proposed, including cryotherapy and topical anthelminthic therapy. However, these treatments require localization of the larvae for effect, which is usually not possible. Repeated application of topical anthelminthics over large areas of skin has been shown to be effective in some cases but this may be impractical. Treatment with albendazole or ivermectin are curative. In severe or relapsing cases, especially with folliculitis, additional doses may be necessary. Children younger than 2 years of age or under 15 kg body weight may be treated with topical preparations.

Oral albendazole is available for human use in the United States.

Oral ivermectin is available for human use in the United States.

Albendazole

Ivermectin