Pelodera Dermatitis

This rare, nonseasonal, acute dermatosis results from invasion of the skin by larvae of the free-living saprophytic nematode Pelodera strongyloides. The larvae are ubiquitous in decaying organic matter and on or near the surface of moist soil but are only occasionally parasitic. Exposure to the larvae occurs through direct contact with infested material such as damp, filthy bedding. The larvae may not be able to invade healthy skin; preexisting dermatoses or environmental conditions favoring maceration of the skin, eg, constant exposure to mud or damp bedding, may facilitate invasion. Pelodera dermatitis has been reported in dogs, cows, horses, sheep, guinea pigs, and people.

Typically, lesions are confined to body areas in contact with the infested material, such as the extremities, ventral abdomen and thorax, and perineum. Affected skin is erythematous and partially to completely alopecic, with papules, pustules, crusts, erosions, or ulcerations. Pruritus is usually intense but can be moderate or even absent. Differential diagnoses include demodicosis, canine scabies, dermatophytosis, pyoderma, and other rare cutaneous larval infestations such as hookworm dermatitis, dirofilariasis, dipetalonemiasis, and strongyloidiasis.

Diagnosis is confirmed easily by finding live, motile P strongyloides larvae in skin scrapings of affected areas. The larvae are cylindrical and ~600 × 38 μm. Histologic examination of skin biopsy specimens reveals larvae in the hair follicles and superficial dermis and usually an inflammatory dermal infiltrate. The larvae are readily cultivated on blood agar plates at 77°F (25°C).

Effective treatment consists primarily of removing and destroying moist, infested bedding material and moving the animal to a clean, dry environment. Usually, spontaneous recovery ensues. It may be desirable to dip or spray the affected animals with an insecticidal preparation at least twice at weekly intervals. Short-term use of corticosteroids may be indicated if pruritus is severe.