Can Moths Cause Allergic Skin Reactions?

Moth-Associated Dermatitis -- Cozumel, Mexico

On December 5, 1989, the Mexican Field Epidemiology Training Program (FETP), Directorate of Epidemiology, Secretariat of Health, was notified of an outbreak of dermatitis among employees of the 17 tourist hotels in Cozumel in October and November. Cozumel, an island located 10 miles off the coast of the Yucatan peninsula of southern Mexico, is 7 miles wide by 35 miles long. The island has 43,000 permanent residents and a daily average of 3000-5000 tourists.

The FETP initiated an investigation by interviewing a probability sample of 417 hotel employees from eight of the 17 hotels (total employees:1436). Because scabies was initially suspected, a case was defined as a person who had onset since July 1 of a rash that itched continually and lasted greater than 1 week. Of the 417 employees, 19 (4.6%) met the case definition. However, 91 (21.8%) reported nonspecific dermatitis of less than 1 weeks' duration since July 1.

During the survey, several persons anecdotally suggested that onset of symptoms followed skin contact with a moth. Moths were noticeably present in Cozumel during October and November but had disappeared by December. The FETP concluded that the outbreak was not scabies and was probably moth-associated. Because all cases had resolved and the likely source was no longer present, no further action was taken.

On January 8, 1990, the FETP was notified of a second outbreak of acute dermatitis among hotel employees and in the general population of Cozumel since January 1. At approximately the same time, thousands of moths had reappeared throughout the island. Using a case definition of "anyone who had presented with erythema, pruritis, and itching between January 1 and 13," the FETP conducted a cluster survey of 10 randomly selected families from each of 30 blocks (n=923 persons); 112 (12.1%) cases were identified. In addition to erythema and pruritis, 23.1% of patients experienced warmth in the area of the rash, and 15.4% had a vesicular component to the rash. Persons most affected were children less than 5 years of age (19.3%), followed by children aged 5-14 years (12.6%) and persons greater than or equal to 15 years (10.6%). Women (14.4%) were more likely than men (10.1%) to have had dermatitis (p=0.04). To examine specific potential risk factors, a case-control study was conducted using 13 patients who had had onset during the 3 days before the investigation and 18 controls (matched for age) from unaffected family members and neighbors. Nine (69.2%) of the patients and none of the controls reported skin contact with moths within 3 days before onset of symptoms (p less than 0.01; odds ratio=infinity; 95% confidence interval=5.4-infinity).

To assess the effect of direct contact exposure of skin to moths, the body and wings of a live moth were rubbed on the forearms of six volunteers from the Cozumel health center. Within 5 minutes, five of the six developed an intense pruritis, followed by an erythematous rash. Symptoms lasted 3 days. An entomologic study classified the insect as belonging to the family Saturnidae, genus Hylesia, species alinda Druce, which has a 3-month generational cycle.

Suggested control measures included replacing the clear light bulbs of the hotels with yellow insect-repelling bulbs, installing electric insect traps on the grounds of the hotels, and spraying insecticide around the borders of the hotels. Because a third outbreak is expected in association with the next generation of moths, community vector control is being planned. Entomologists suggest that the natural parasites of this moth likely will return within a year, causing a natural decline in the population of Hylesia moths. Active epidemiologic and entomologic surveillance is in place. Reported by: A Villanueva, MD, Secretariat of Health, State of Quintana Roo; C Beutelspacher, PhD, Instituto de Biologia, Universidad Nacional Autonoma de Mexico; G Fernandez, MD, E Morales, MD, M Aparicio, MD, G Castro, MD, E Gil, MD, M Luna, MD, A Moreno, MD, C Ruiz, MD, Field Epidemiology Training Program, Secretariat of Health; J Sepulveda, MD, Director, Div of Epidemiology, Secretariat of Health, Mexico. Div of Field Svcs, Epidemiology Program Office, CDC.