Epidemic dermatitis due to contact with a moth in Cozumel, Mexico

In early December 1989, an outbreak that was initially thought to be scabies was investigated among employees of tourist hotels in Cozumel, Mexico. Of 417 employees interviewed, only 19 (4.6%) met a case definition for scabies dermatitis, while 91 (21.8%) reported a nonspecific dermatitis of less than one-week's duration. Persons with nonspecific dermatitis related the onset of their dermatitis to skin contact with a moth that had been present in large numbers in November. At the time of the initial investigation in December, there were no active cases of dermatitis and the moth was no longer present. During early January 1990, numerous cases of dermatitis again began to be reported. Using a case definition for nonspecific dermatitis, a survey of Cozumel's resident population showed an attack rate of 12.1%. A case-control study revealed the only significant risk factor to be skin contact with the suspect moth (P less than 0.01), which had returned in large numbers. Six health workers volunteered to have the moth rubbed on their skin; within 5 min, five of six developed an intense pruritus followed by an erythematous rash. The moth was classified as Hylesia alinda Druce. This species has nettling hairs on its abdomen that excrete a histamine-like substance. Although this moth is normally present in small numbers in Cozumel, the passage of hurricane Gilbert killed most of its natural predators (wasps and bees), allowing its population to overgrow. No control measures were undertaken because the moth's natural predators returned that spring and dramatically reduced the moth population. No further outbreaks of dermatitis occurred.