Rhabditic Dermatitis in Animals

Dermatitis caused by Rhabditis (formerly Pelodera) is a rare, nonseasonal, acute dermatosis that results from invasion of skin by larvae of the free-living saprophytic nematode Rhabditis strongyloides.

R strongyloides larvae are ubiquitous in decaying organic matter and on or near the surface of moist soil; only occasionally, however, are they parasitic. Animals are exposed to the larvae 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) can facilitate invasion. Rhabditic dermatitis has been reported in dogs, cows, horses, sheep, guinea pigs, and humans.

Typically, R strongyloides–induced lesions are confined to body areas in contact with 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 for rhabditic dermatitis include demodicosis, canine scabies, dermatophytosis, pyoderma, and other rare cutaneous larval infestations, such as hookworm dermatitis, dirofilariasis, dipetalonemiasis, and strongyloidiasis.

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

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