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Epidemiologic Notes and Reports Rash Illness Associated with Gypsy Moth Caterpillars -- Pennsylvania

Between the end of April and the third week of May 1981, an increase in rash illness was reported by 2 schools in Luzerne County, in northeast Pennsylvania. School A had an enrollment of 320 students, with 135 affected by rashes (an attack rate of 42.2%). School B had 76 out of 300 students affected (an attack rate of 25.3%). The symptoms included pruritic rash and occasional urticaria. Fever, nausea, vomiting, diarrhea, and chills were seldom reported. The rash was generally located on exposed areas of the body--75.4% on arms, 22.8% on the neck, and 21.1% on legs. Rash was less often observed on the back, stomach, face, chest, or hands. The median duration of the rash for school A was 7 days, and for school B, 4 days. All skin scrapings of the rash for bacteria were negative; throat and stool cultures, and tests of acute- and convalescent-phase serum specimens to detect viruses were also negative.

A group of well students from the same schools were selected as controls. All students were interviewed for history of outdoor exposure. Touching caterpillars (p 0.01), working in a garden (p 0.05), and going fishing (p 0.01) were statistically associated with rash illness, whereas a history of allergies was not.

Of the cases with known dates of onset, 27.5% occurred during the first week of May. This period coincides with the first larval instar of gypsy moth caterpillars, which occurs between the first and fourth weeks of May in this area. No new cases were reported after the third week of May. School A is located in a heavily wooded rural area, and school B in a small town with many trees. A distribution map of gypsy moth location indicates highest concentration in the areas in which these schools are located.

The temporal and geographic association between the outbreak of rash illness and the prevalence of gypsy moth larvae suggest a causal relationship may exist. Reported by R Aber, MD, Hershey Medical Center, T DeMelfi, T Gill, B Healey, MPA, MA McCarthy, RN, N Oswell, W Ruhig, H Speziale, RN, EJ Witte, VMD, State Epidemiologist, Pennsylvania Dept of Health.

Editorial Note

Editorial Note: Skin diseases resulting from contact with members of the Order Lepidoptera were described in ancient Greek medical writings. In 1901, several U.S. patients were reported to have experienced dermatitis following contact with Euproctis chrysorrha (brown-tailed moth) larvae (1). Several outbreaks of dermatitis caused by Lepidoptera have been reported; the largest outbreak involved 600 cases among 6,000 soldiers in Israel (2,5). Clinical symptoms and signs are quite variable depending on the type of insect and its stage of development when encountered, the intensity and duration of exposure, the pathogenetic mechanism involved, and the susceptibility of the host. Disease is usually caused by direct contact with the insect or its parts, but indirect contact and airborne transmission have been documented. At least 3 pathogenetic mechanisms have been described: l) intracutaneous injection of toxic substance(s) through hollow appendages (setae) of the insect, 2) direct irritant effects of insect hairs or appendages, and 3) hypersensitivity reaction to insect antigen. A biphasic reaction to skin testing with insect antigens has been described among some patients, which may represent sequential occurrence of 2 or more of these mechanisms (6).

The gypsy moth (Lymantria dispar) is a serious threat to hardwood trees in the northeastern United States (7). It was introduced into the Boston area in 1869 and has been spreading concentrically. Despite heavy infestation in the Northeast, skin diseases have seldom been attributed to the insect except in special laboratories where staff work with the moth and its larvae. No community outbreaks had been reported before 1981, when outbreaks of skin disease attributed to the gypsy moth were reported from Connecticut, Massachusetts (8), Rhode Island (9), and Pennsylvania. These outbreaks are believed to have been caused by contact with early larval stages of the moth, which are highly mobile and airborne. It is also possible that the disease is caused by a chemical substance that the larvae acquire during pest control programs. Primary-care physicians and dermatologists should be aware of skin disease resulting from contact with gypsy moth larvae.


  1. White JC. Dermatitis produced by a caterpillar. Boston Med Surg J 1901;144:599.

  2. Hillier FF, Warm RP. Caterpillar dermatitis. Brit Med J 1967;1:346-8.

  3. McGovern JP, Barkin GD, McElhenney TR, Wende R. Megalopyge opercularis. Observations of its life history, natural history of its sting in man, and report of an epidemic. JAMA 1961;175:1155-8.

  4. Hill WR, Rubenstein AD, Kovacs J Jr. Dermatitis resulting from contact with moths (Genus Hylesia). JAMA 1948;138:737-40.

  5. Ziprkowski L, Hofski E, Tahori AS. Caterpillar dermatitis. Israel Med J 1959;18:26-31.

  6. Goldman L, Sawyer F, Levine A, Goldman J, Goldman S, Spinanger J. Investigative studies of skin irritations from caterpillars. J Invest Derm 1960;34:67-9.

  7. Pennsylvania Department of Environmental Resources. The gypsy moth. Harrisburg, Pa. December, 1980 (revision).

  8. Northeastern Forest Experiment Station News. USDA Forest Serv, May 1981.

  9. Rhode Island Disease Bulletin. Caterpillar-associated rashes in Northwest Rhode Island. 1981;18.

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