Bot-Fly Maggot Infestation in Latin America

Abstract

Infestation by bot-fly larvae is a major obstacle to beef and dairy production in Latin America. It is also a widespread, underreported human health problem. Because of its unique harnessing of transporter insects in egg dispersal, the adult fly is unseen and unknown among the rural people whom it plagues. Traditional methods of maggot removal from humans are being replaced by treatment with highly dangerous pesticides, several of which are banned in the United States because of their carcinogenicity and other adverse effects. There is urgent need for epidemiological evaluation and assessment of health risks associated with pesticide treatment. MA AGGOT infestation by the bot fly (Dermatobia hominis) is a seriously debilitating disease of cattle throughout tropical America. Accounts of pesticide trials against the larvae feature prominently in the literature of veterinary medicine. However, human cases are virtually unreported medically, except for infestations that occur among European and North American visitors returning from Central and South America. Remarkably absent are data on prevalence, morbidity, and adaptation among indigenous peoples who occupy endemic zones and face bot-fly infestation on a daily basis. A preliminary investigation of the disease in a small area of Guatemala involved several clusters of households in three scattered hillside settlements; the results provide family-level insight about the infestation. The account that follows describes the life cycle of the fly, its continental distribution, the economic effects on the cattle industry, and the traditional response to human infestation. My observations in Guatemala draw attention to bot-fly prevalence and pathology among rural populations and, specifically, to modern changes in self-treatment that are seriously threatening to human health. GEOGRAPHICAL DISTRIBUTION The bot fly belongs to the order Diptera (two-winged flies) and the family Cuterebridae (robust bot flies). Cuterebrid bot-fly maggots are precocious saprophages in that they feed on living tissues; hence their capacity to produce pathological outcomes in vertebrate hosts (James 1947; Harwood and James 1979). Dermatobia hominis is the sole species of human bot fly and is found only in the New World (Fig. 1). Its range extends from slightly * The research was supported in part by a grant from the Committee on Research and Exploration of the National Geographic Society. I am indebted to Richard Merritt for identifying the larvae and to Robert K. Ringer, John D. Parmer, Larry G. Olsen, and Robert H. Popenga for assistance in identifying pesticides. * DR. HUNTER is a professor of geography and community health science at Michigan State University, East Lansing, Michigan 48824. This content downloaded from 157.55.39.163 on Wed, 21 Sep 2016 05:19:30 UTC All use subject to http://about.jstor.org/terms BOT-FLY INFESTATION IN LATIN AMERICA FIG. 1.-Distribution of the bot fly in Central and South America. Source: After Roncalli 1984. (Cartography by Ellen B. White) north of 20? north in southern Mexico to approximately 34? south in northern Argentina. The species eschews desert and altiplano South America and is typically found below 1,500 meters elevation. A habitat of warmth and moisture is essential, but the fly is well adapted to the seasonal wet-dry alterations of a tropical climate (Catts 1982; Roncalli 1984). This species shows a strong preference for shaded areas of forest, forest edge, or woodland. In agricultural regions, it favors hillside brush and scrub, and riverine or gallery forest. The extensive environmental range, combined 383 This content downloaded from 157.55.39.163 on Wed, 21 Sep 2016 05:19:30 UTC All use subject to http://about.jstor.org/terms THE GEOGRAPHICAL REVIEW with a capacity to adapt to virtually any vertebrate host for larval sustenance, ensures the fly's tenacious presence in the countryside of Latin America (Table I). Except for cases that proved to be imported from Brazil and Colombia, the species is unreported in Chile, where conditions of rainfall and temperature are unfavorable. It is also unreported in El Salvador but undoubtedly exists there, because heavily endemic zones occupy the Guatemalan and Honduran borderlands. Infestation also occurs on Trinidad, where TABLE I-BOT-FLY PREVALENCE IN CENTRAL AND SOUTH AMERICA