Bot flies, particularly the human bot fly (Dermatobia hominis), are a subject of considerable interest and, understandably, some concern. Often described as resembling bumblebees due to their size and hairy bodies, these flies are more than just a buzzing nuisance. The key question for many, especially travelers and those living in or visiting certain regions, is: Where Are Bot Flies Found? Understanding the geographic distribution of these insects is crucial for awareness and prevention of myiasis, the infestation caused by their larvae.
Primarily, the human bot fly is indigenous to the warm climates of Central and South America. This region represents their natural habitat, and it’s within these borders that most bot fly encounters occur. Let’s delve deeper into the specific areas where Dermatobia hominis thrives.
Distribution of the Human Bot Fly: A Geographical Overview
The Dermatobia hominis bot fly’s distribution spans a significant portion of the Americas, ranging from Mexico in North America down to Paraguay and northeastern Argentina in South America. This broad range encompasses a variety of countries and ecosystems, all sharing the warm, often tropical or subtropical, conditions that these flies prefer.
More specifically, the bot fly’s habitat includes:
- Mexico: The northernmost extent of their known range.
- Central America: Countries such as Belize, Guatemala, Honduras, Nicaragua, Costa Rica, and Panama are all within the bot fly’s distribution area.
- South America: A large part of the continent is considered bot fly territory. This includes countries like Colombia, Venezuela, Guyana, Suriname, French Guiana, Brazil, Ecuador, Peru, Bolivia, and parts of Argentina and Paraguay.
It’s important to note that while these are the generally recognized boundaries, sporadic cases can occur outside these areas, typically when travelers return from bot fly-endemic regions carrying the parasite. This highlights the importance of awareness even for those in non-native areas.
Figure 1. Geographical distribution of the human bot fly, Dermatobia hominis. Drawing by C. Roxanne Connelly, University of Florida.
Habitats and Environment
Within these countries, bot flies are found in a variety of habitats, generally favoring rural and forested areas where their primary hosts, such as cattle, are prevalent. They are less common in urban environments, though proximity to rural areas can still pose a risk.
Key environmental factors influencing their distribution include:
- Warm Climate: Bot flies thrive in warm, humid climates. Tropical and subtropical regions provide the ideal conditions for their life cycle and survival.
- Forests and Woodlands: These environments offer shade, humidity, and are often home to the blood-feeding insects that bot flies use as carriers for their eggs.
- Cattle Farming Regions: As cattle are major hosts, areas with significant cattle farming are often hotspots for bot fly activity.
- Proximity to Wildlife: Bot flies can also affect a range of wild animals, so areas with diverse wildlife populations can also harbor these flies.
Understanding the Bot Fly
To better understand why their location is important, it’s helpful to know a bit more about the bot fly itself. Adult Dermatobia hominis flies are notable in appearance, often mistaken for bumblebees due to their size and dense hair covering. They range from 12 to 18 mm in length and exhibit a mix of colors, including a yellow face, metallic blue abdomen, and orange legs.
Figure 2. Lateral view of an adult human bot fly, Dermatobia hominis. Photograph by Lyle J. Buss, University of Florida.
Figure 3. Frontal view of an adult human bot fly, Dermatobia hominis. Photograph by Lyle J. Buss, University of Florida.
Figure 4. Dorsal view of an adult human bot fly, Dermatobia hominis. Photograph by Lyle J. Buss, University of Florida.
However, it’s not the adult fly that directly causes concern for humans, but rather its larval stage. The bot fly life cycle is quite unique and contributes to their distribution and impact.
The Intriguing Life Cycle and Myiasis
Female bot flies have a fascinating method of egg delivery known as phoresy. Instead of directly laying eggs on a host, they capture blood-feeding insects like mosquitoes or ticks mid-flight. They then attach their eggs to these carriers. When the carrier insect lands to feed on a warm-blooded animal (including humans), the change in temperature triggers the bot fly eggs to hatch.
The larvae then burrow into the skin through the bite wound or hair follicles. Once inside, the larva develops through three stages (instars) in the subcutaneous layer. These larvae breathe through spiracles at the skin’s surface, creating a painful lesion or pustule. This infestation is myiasis.
Figure 5. Instars of the human bot fly larva (1st, 2nd, early 3rd, and late 3rd). Photograph by Francisco M. Marty, M.D. and Kristen R. Whiteside, B.S., Brigham and Women’s Hospital, Boston, MA.
Figure 6. Third instar larva of the human bot fly, lateral view. Photograph by Lyle J. Buss, University of Florida.
Figure 7. Third instar larva of the human bot fly, frontal view. Photograph by Lyle J. Buss, University of Florida.
Figure 8. Backward projecting spines on larva of the human bot fly. Photograph by C. Roxanne Connelly, University of Florida.
Figure 9. Posterior spiracles of the larva of the human bot fly. Photograph by C. Roxanne Connelly, University of Florida.
Figure 10. Side view of posterior spiracles of the larva of the human bot fly. Photograph by C. Roxanne Connelly, University of Florida.
Figure 11. Third instar larva of the human bot fly. Photograph by C. Roxanne Connelly, University of Florida.
After several weeks of feeding on tissue exudates, the mature larva exits the host to pupate in the soil, eventually emerging as an adult fly to continue the cycle.
Hosts and Human Interaction
While named the “human bot fly,” Dermatobia hominis has a wide range of hosts. Cattle and dogs are the most common, but they can infest various warm-blooded animals, including:
- Cattle
- Dogs
- Cats
- Sheep
- Pigs
- Monkeys
- Rabbits
- Buffalo
- And, occasionally, humans
Humans are accidental hosts. Infestation typically occurs when people are in bot fly habitats and are bitten by carrier insects carrying bot fly eggs.
Symptoms, Treatment, and Management of Myiasis
The primary symptom of human bot fly myiasis is a painful, boil-like lesion on the skin. This lesion may secrete fluids, and some individuals can even feel the larva moving beneath the skin.
Figure 12. Raised lesion on the skin caused by human bot fly larva. Photograph by Francisco M. Marty, M.D. and Kristen R. Whiteside, B.S., Brigham and Women’s Hospital, Boston, MA.
Treatment usually involves removing the larva. Common methods include:
- Surgical Removal: A simple procedure under local anesthesia to extract the larva.
- Suffocation Method: Covering the breathing spiracles of the larva with substances like petroleum jelly or beeswax to force it to emerge.
- Pressure Extraction: Applying pressure around the lesion to pop out the larva.
After removal, antibiotics are often prescribed to prevent secondary infections. The wound typically heals within a couple of weeks with minimal scarring.
Preventing bot fly myiasis is key, especially for travelers to endemic regions. Preventative measures include:
- Insect Repellent: Using DEET-based repellents on skin and clothing.
- Protective Clothing: Wearing long sleeves and pants to minimize skin exposure.
- Vector Control: In endemic areas, efforts to control populations of carrier insects like mosquitoes and ticks can help reduce bot fly transmission.
Conclusion: Awareness and Location are Key
Understanding where bot flies are found is the first step in mitigating the risk of myiasis. Primarily located in Central and South America, these flies thrive in warm, rural environments. While human infestation is not common, awareness is crucial for those living in or traveling to these regions. By taking preventive measures and understanding the bot fly’s life cycle and distribution, individuals can significantly reduce their risk of encountering this fascinating, albeit unwelcome, parasite.
References
- Acha P, Szyfres B. 1994. Zoonoses and communicable disease common to man and animals. 2nd Edition. Scientific Publication No. 503. Pan American Health Organization. WHO, Washington, D.C. 963 pp.
- Cornet MM, Florent A, Lefebvre C, Wertheimer CP, Bangs M, Bouvet A. 2003. Tracheopulmonary myiasis caused by a mature third-instar Cuterebra larva: case report and review. Journal Clinical Microbiology 41: 5810-5812.
- Diaz JH. 2006. The epidemiology, diagnosis, management, and prevention of ectoparasitic diseases in travelers. Journal of Travel Medicine 13: 1195-1982.
- Fernandes FF, Linardi PM, Chiarini-Garcia H. 2002. Morphology of the antenna of Dermatobia hominis (Diptera: Cuterebridae) based on scanning electron microscope. Journal of Medical Entomology 39: 36-43.
- Fernandes FF, Chiarini-Garcia H, Linardi PM. 2004. Scanning electron microscopy studies of sensilla and other structures of adult Dermatobia hominis (L. Jr., 1781) (Diptera:Cuterebridae). Journal of Medical Entomology 41: 552-560.
- Haruki K, Hayashi T, Kobayashi M, Katagiri T, Sakurai Y, Kitajima T. 2005. Myiasis with Dermatobia hominis in a traveler returning from Costa Rica: Review of 33 cases imported from South America to Japan. Journal of Travel Medicine 12: 285-288.
- Kahn DG. 1999. Myiasis secondary to Dermatobia hominis (Human Botfly) presenting as a long-standing breast mass. Archives of Pathology and Laboratory Medicine 123: 829-831.
- Lawson RD, Rizzo M. 2005. Digital infestation with the human bot fly. Journal of Hand Surgery 30B: 490-491.
- Lang T, Smith DS. 2003. Wiggling subcutaneous lumps. Clinical Infectious Diseases 37: 2087-2088.
- Liebert PS, Madden RC. 2004. Human botfly larva in a child’s scalp. Journal of Pediatric Surgery 39: 629-630.
- Maier H, Honigsmann H. 2004. Furuncular myiasis caused by Dermatobia hominis, the human bot fly. Journal of the American Academy of Dermatology 50: S26-S30.
- Matera G, Liberto MC, Larussa F, Barreca GS, Foca A. 2001. Human myiasis: An unusual imported infestation in Calabria, Italy. Journal of Travel Medicine 8: 103-104.
- Marinho CR, Barbosa LS, Granthon de Azevedo AC, de Carvalho Querizo MM, Valgode MA, Aguiar Coelho AM. 2003. Hemilucilia segmentaria (Fabricius, 1805) (Diptera: Calliphoridae) as new biological vector of eggs of Dermatobia hominis (Linnaeus Jr., 1781) (Diptera: Oestridae) in Reserva Biologica do Tingua, Rio de Janeiro, Brazil. Memórias do Instituto Oswaldo Cruz 98: 937-938.
- Marty FM, Whiteside KR. 2005. Myiasis due to Dermatobia hominis (Human Botfly). New England Journal of Medicine 23: 352.
- Millikan LE. 1999. Myiasis. Clinical Dermatology 17: 191-195.
- Pereira MCT, Leite VHR, Leite ACR. 2001. Experimental skin lesions from larvae of the bot fly Dermatobia hominis. Medical and Veterinary Entomology 15: 22-27.
- Rossi MA, Zucoloto S. 1973. Fatal cerebral myiasis caused by the tropical warble fly, Dermatobia hominis. American Journal of Tropical Medical Hygiene 22: 267-269.
- Safdar N, Young DK, Andes D. 2003. Autochthonous furuncular myiasis in the United States: Case report and literature review. Clinical Infectious Diseases 36: e73-80.
- Saliba EK, Oumeish YO, Oumeish I. 2002. Epidemiology of common parasitic infections of the skin in infants and children. Clinical Dermatology 20: 36-43.
- Sampson C E, MaGuire J, Eriksson E. 2001. Botfly myiasis: case report and brief review. Annals of Plastic Surgery 46: 150-152.
- Schwartz E, Gur H. 2002. Dermatobia hominis myiasis: An emerging disease among travelers to the Amazon Basin of Bolivia. Journal of Travel Medicine 9: 97-99.
- Tamir J, Haik J, Orenstein A, Schwartz E. 2003a. Dermatobia hominis myiasis among travelers returning from South America. Journal of the American Academy of Dermatology 48: 630-632.
- Tamir J , Haik J, Schwartz E. 2003b. Myiasis with Lund’s fly (Cordylobia rodhaini) in travelers. Journal of Travel Medicine 10: 293-295.
- Villarino M A, Garcia O, Fussell W, Preston K , Wagner GG. 2003. An initial survey of the cattle grub Dermatobia hominis (L. Jr.) in Nicaragua. Preventive Veterinary Medicine 61: 333-338.
