Caterpillar dermatitis refers to an acute inflammatory skin reaction caused by the venom released from the poisonous hairs of caterpillars after they puncture the skin. In China, common pathogenic caterpillars include the mulberry caterpillar, pine leaf caterpillar, and stinging caterpillar.

bubble_chart Etiology

Disease cause: Euproctis similis dermatitis. The Euproctis similis is the larva of the mulberry tussock moth, which feeds on mulberry leaves and various fruit trees, willow, elm, and other leaves. Therefore, this disease is commonly seen in those engaged in mulberry orchard or fruit orchard labor. The peak period for Euproctis similis outbreaks is from June to October. The larvae's bodies are covered with toxic hairs, with a mature larva possessing as many as 2 to 3 million toxic hairs. These hairs are arrow-shaped, measuring 45–315 μm in length, with needle-like bases that easily detach from the larva's body. The hollow, tube-like toxic hairs contain venom and are often dispersed by the wind. If they land on the skin, their sharp tips can penetrate it, causing dermatitis within minutes to hours.

bubble_chart Clinical Manifestations

This disease is commonly seen in summer and autumn, especially during hot, dry, and windy weather, which facilitates the dispersal of toxic hairs. At this time, people often wear short-sleeved shirts and engage in outdoor activities, increasing their chances of exposure to toxic hairs. As a result, outbreaks often occur in batches within the same area. The rash frequently appears on the neck, shoulders, upper back, upper chest, and the flexural surfaces of the limbs. The primary lesions consist of edematous maculopapules and papules, ranging in size from mung bean to soybean, with a pale or bright red color. A few cases may present as papulovesicles, often with a puncture mark from a toxic hair at the top. The lesions are generally scattered and cause intense itching, particularly at night. The course of the disease typically lasts about a week. If toxic hairs adhere to the eyelid and are rubbed into the eye, they can cause conjunctivitis.

The detection of Euproctis similis venomous hairs at the rash site aids in confirming the diagnosis. The method involves examining the rash with a magnifying glass to locate the venomous hairs or repeatedly applying clear adhesive tape to the rash, then placing it on a slide. Add a drop of xylene, cover with a coverslip, and examine under a microscope.

bubble_chart Treatment Measures

Treatment involves topical application of anti-inflammatory and antipruritic agents. Adhesive tape can be repeatedly applied to the affected area to remove residual toxic hairs on the skin, avoiding further irritation such as scratching. Oral antihistamines may be administered as needed.

bubble_chart Prognosis

Prevention should focus on early eradication of overwintering and early spring tussock moths, commonly using sprays like trichlorfon, polyhedral virus sprays, and protecting natural enemies for biological control. When working under or on trees infested with tussock moths, pay attention to wind direction and wear protective clothing and hats.