Paederus dermatitis in Adult
The Paederus beetle does not sting or bite, but accidental contact with or crushing of the beetle on skin results in the release of the coelomic fluid containing the irritant pederin. Initially painless, over the course of 12-36 hours, the contact site begins to burn, sting, and itch.
Erythematous patches first appear and are followed by vesicles, which coalesce into bullae over the course of several days. Affected areas appear similar to chemical or thermal burns, but the clinical symptoms of burning and itching are relatively mild and disappear within a few days. The skin manifestations persist 1-3 weeks as vesicles, pustules, and bullae; lesions then crust, scale, and eventually desquamate without scarring. Postinflammatory hyperpigmented patches are transient but may last months. Atypical variants may present with more systemic skin involvement and symptoms of more severe burning and itching, fever, neuralgia, arthralgia, and vomiting.
PD size, shape, severity, and location are case dependent but typically involve exposed skin. Periorbital involvement is common, with unilateral periorbital edema and keratoconjuctivitis due to secondary transfer of the irritant from the hands to the face (referred to as Nairobi eye in East Africa).
Paederus beetle species are distributed worldwide, typically living in moist environments (eg, near lakes, marshes, and flood plains) and hot, tropical climates, scavenging debris and the larvae of other insects. While they are able to fly, they prefer to run, characteristically curling when disturbed. The beetles are 7-10 mm long, 0.5-1 mm wide, and are recognized by their distinct black head, red-orange abdomen, black posterior tip of abdomen, and metallic blue or green wings. Paederus beetles are nocturnal and are attracted to artificial lighting, particularly ultraviolet lights (eg, insect electrocution devices) and white lights (eg, fluorescent lights).
PD has a wake-and-see presentation, with beetle exposure occurring inadvertently overnight and skin manifestations appearing in the morning. Patients may not recall seeing any arthropods and will deny recent stings or bites. Incidence of PD is seasonal, with rates peaking during the spring and summer and dropping off significantly as ambient temperatures decrease during the fall. Risk factors include outdoor activities (eg, agriculture, gardening, or military patrols) and working at night in well-illuminated areas (eg, security guards). While the rapid appearance of vesicles and bullae can be concerning, PD often has a mild clinical course that self-resolves over several weeks. Early identification can prevent unnecessary diagnostic tests and treatments and help avoid further outbreaks.
L23.89 – Allergic contact dermatitis due to other agents
402149002 – Dermatosis due to beetle
- Cantharidin dermatitis (blister beetle dermatitis) – Meloidae and Oedemeridae beetle families produce cantharidin, another potent vesicant. Cantharidin dermatitis blisters within 24 hours of exposure and is distinguished by its noninflammatory vesicles and bullae compared with the intensely erythematous skin associated with PD.
- Acute allergic contact dermatitis (eg, poison ivy, oak, and sumac) – Usually does not blister and has more significant itching compared with PD. Less likely in young children.
- Phytophotodermatitis – Linear or haphazard erythema and edema that may be accompanied by delayed blister formation. Recent plant exposure.
- Thermal burns or chemical burns (chemical burns are covered individually according to chemical agent, eg, hydrogen fluoride burn) – Symptoms of burns are more severe and will have a longer clinical course. Multiple cases of PD have been mistaken for chemical weapon exposure (eg, vesicant exposure) following nighttime military exercises and patrols due to similar presentation.
- Herpes zoster – Follows unilateral dermatomal pattern, preceded by a history of varicella. Tzanck smear and direct fluorescent antibody (DFA) positive.
- Herpes simplex – Discrete groupings of painful vesicles. Tzanck smear and DFA positive.
- Bullous impetigo – Painful red rash with fragile bullae and honey-colored crusting. Gram staining of blister fluid will reveal gram-positive cocci. It may be difficult to distinguish from PD that has become secondarily impetiginized.
- Preseptal cellulitis – Periorbital swelling and redness. Patient may appear toxic and febrile and have significant leukocytosis. Eyelid is often warm to the touch.
- Angioedema – Edema of the subcutaneous or submucosal tissues involving eyelids (bilaterally), lips, and tongue. Transient, with swelling in less than 24 hours.
- Urticaria – Does not form vesicles or bullae.
- Acute glomerulonephritis – Periorbital edema, but not associated with inflammatory vesicles and bullae. If clinical suspicion, order urine analysis.