Dermatitis after exposure to Lymantria dispar dispar.

In early June 2021, a 60-year-old man presented to our emergency department with 4 days of progressive facial swelling and pruritic rash that was not responsive to valacyclovir (Figure 1). Slit-lamp examination did not suggest herpes zoster or ophthalmia nodosa.

Figure 1:

Photographs showing dermatitis in a 60-year-old man after contact with Lymantria dispar dispar. The patient had (A) periorbital edema and poorly demarcated erythematous plaques with serous crusting, and (B) erythematous lichenified and annular plaques on the posterior neck.

Sixteen hours before onset, he had been removing and shaking a burlap trap, placed because of a local infestation of Lymantria dispar dispar moths. He reported no previous reactions to latex, atopy nor prior contact with this moth species, but reported annual infestations of L. dispar dispar on his property since 2019.

We treated the patient with prednisone (20 mg once a day for 7 days), and his lesions resolved in 3 weeks. Two weeks later, he developed a similar eruption 1 day after weeding under a maple tree infested with L. dispar dispar. This cleared after another 2 weeks of prednisone, which was then tapered, with no recurrence.

Our patient’s delayed-onset dermatitis with a history of exposure to L. dispar dispar, which recurred after another exposure, strongly supports a diagnosis of allergic contact dermatitis from this moth species. Our differential diagnoses included other causes of allergic contact dermatitis (such as latex and urushiol, the hapten in poison ivy, poison oak and sumac), irritant contact dermatitis and herpes zoster, but we considered these unlikely because of the distribution, delayed onset and pruritus, respectively.

Lymantria dispar dispar is invasive to North America, spreading at about 21 km/year over 7- to 10-year cycles of expansion. Epidemic outbreaks of dermatitis have been reported since 1981; a cross-sectional study of 2 towns in Massachusetts affected by an epidemic in 1982 showed rash rates of 1.6% and 10.4%.1,2

In 2019, an outbreak was declared in southern Ontario, with a yearly increase in severity through 2021.1 Acute contact dermatitis from L. dispar dispar is thought to be both a type IV hypersensitivity reaction and related to histamine released from the caterpillar’s hairs.1 Importantly, the fine hairs may be disrupted and aerosolized; ocular penetration can cause ophthalmia nodosa and may require referral to an ophthalmologist.3 Greater awareness among clinicians of L. dispar dispar as a possible cause of severe delayed-onset hypersensitivity requiring prednisone, as well as public education on the use of thick protective garments including eyewear when handling the caterpillars, is important while this moth species is epidemic in Canada.