Bot flies, often associated with tropical regions, might seem like an exotic concern far removed from everyday life in America. However, the reality is more nuanced. While dramatic cases of tropical botfly infections capture attention, a lesser-known type of botfly, belonging to the genus Cuterebra, is indeed present in North America. These flies, while not as notorious as their tropical cousins, can cause a condition called myiasis, the infestation of tissues with fly larvae. This article explores the presence of bot flies in America, focusing on Cuterebra infections and what you need to know.
What are Bot Flies and Myiasis?
Bot flies are a family of flies (Oestridae) whose larvae are parasitic in mammals. Myiasis, in its simplest terms, is the infestation of living vertebrate animals with dipterous larvae, which feed on the host’s dead or living tissue, liquid body substances, or ingested food. There are different types of myiasis, categorized by the fly species and how they interact with their host. Some flies cause obligatory myiasis, meaning their larvae require a living host to develop. Others cause facultative myiasis, where they typically lay eggs in decaying matter but can also infest wounds or tissues of living animals.
Human myiasis is most commonly caused by bot flies, flesh flies (Sarcophagidae), blow flies (Calliphoridae), and house flies (Muscidae). Obligatory myiasis in humans is frequently linked to Dermatobia hominis (human botfly) found in the American tropics, and Cordylobia species in Africa. But what about bot flies in the United States and Canada?
Cuterebra Bot Flies: The North American Culprits
The genus Cuterebra represents the primary bot flies endemic to North America. With approximately 40 species in North America out of about 70 worldwide, these flies are a native part of the ecosystem. Their natural hosts are typically rodents, rabbits, and hares. However, domestic animals like cats and dogs, and even humans, can become accidental hosts.
Cuterebra bot flies have a fascinating life cycle. Female flies lay eggs near the burrows of their rodent hosts or along animal trails. The eggs hatch in response to warmth, often triggered by the body heat of a passing host. First-stage larvae then attach to a host, typically entering through natural openings like the nose or mouth, or by directly penetrating the skin.
Once inside, the larvae of some species may migrate through tissues before settling under the skin. Here, they develop through second and third larval stages. Mature larvae eventually emerge from the host to pupate in the soil and complete their life cycle.
Cuterebra Myiasis in Humans: A Rare but Real Occurrence
While Cuterebra bot flies primarily target animals, human infections, though rare, do occur in North America. Cases are not widely reported, with only about 60 documented in the last 70 years. These infections usually manifest as furuncular myiasis, where a larva develops in a boil-like lesion under the skin. In rarer instances, larvae can cause respiratory myiasis, as highlighted in a case report from northern New York State.
Case Report: Respiratory Myiasis in New York
In August 2017, a 28-year-old man in northern New York, who had not traveled outside the state, presented with a cough and chest tightness. After two days, he coughed up what appeared to be a parasite. He worked on an organic farm and had exposure to horse manure and compost. Intriguingly, his pet cat had recently brought a dead mouse into his bed.
Upon examination, the “parasite” was identified as a bot fly larva. Further analysis confirmed it to be a second-instar larva of Cuterebra. This diagnosis was based on the larva’s physical characteristics and the exclusion of tropical botfly species due to the patient’s lack of travel history.
Fig. 1
Figure 1: Bot fly larva specimen. Panel A shows a macroscopic view on a microscope slide. Panel B shows a microscopic view at 10x magnification, highlighting key morphological features for identification.
This case underscores that Cuterebra myiasis can occur in non-tropical regions of America and can present in unexpected ways, such as respiratory involvement. The patient’s exposure to potentially contaminated soil or the dead mouse in his home were considered likely sources of infection.
Diagnosing Cuterebra Myiasis
Diagnosing myiasis typically involves identifying the larvae. In the case of Cuterebra, identification to the genus level is usually sufficient for patient care. However, species-level identification can be helpful for epidemiological understanding.
Identifying bot fly larvae can be challenging, especially in their early stages. Keys and guides often focus on third-instar larvae, and the appearance of second-instar larvae can be quite different. In the New York case, diagnosis relied on morphological features like the larva’s shape, spines on body segments, and the spiracular plates, which are breathing organs on the larva. The patient’s location and lack of travel also helped rule out tropical botflies.
Are You at Risk? Prevention and Awareness
While Cuterebra myiasis is rare in humans, understanding potential risk factors and taking preventive measures is wise, especially if you live in or visit areas where these flies are prevalent. Risk factors can include:
- Outdoor Activities: Gardening, farming, hiking, or any activity that increases exposure to soil, rodents, and their habitats.
- Living in Rural or Semi-Rural Areas: These areas are more likely to have populations of Cuterebra host animals.
- Contact with Animals: Handling wild rodents or allowing pets to roam and potentially bring infected animals or materials into the home.
Prevention strategies include:
- Protective Clothing: When gardening or working outdoors in potentially exposed areas, wear gloves, long sleeves, and pants.
- Hygiene: Wash hands thoroughly after outdoor activities, especially before eating.
- Pet Care: Control rodents around your home. If your pets hunt, check them for any signs of lesions or unusual lumps.
- Awareness: Be aware of the possibility of bot fly myiasis if you develop an unexplained boil or respiratory symptoms after potential exposure.
If you suspect you might have myiasis, seek medical attention. While most Cuterebra myiasis cases are not serious and larvae can be removed, proper diagnosis and care are essential.
Conclusion: Bot Flies in America are a Reality
So, Are There Bot Flies In America? Yes, Cuterebra bot flies are present and native to North America. While human infections are uncommon, they are a documented reality, even in non-tropical regions like the northeastern United States. Understanding the life cycle of these flies, recognizing potential risks, and practicing preventive measures can help minimize the already low chance of encountering Cuterebra myiasis. This case report serves as a reminder that even seemingly exotic medical conditions can occur closer to home than we might think, highlighting the importance of awareness and accurate diagnosis.
References
[1] Baird JK, Baird CR, Sabrosky CW. North American cuterebrid myiasis. J Am Acad Dermatol. 1989 Jun;20(6):1057-61.
[2] Anderson GS, Belton P. Myiasis in humans and domestic animals in British Columbia, 1990-1995. J Entomol Soc Br Columbia. 1996;93:75-81.
[3] Colwell DD, Hall MJR, Scholl PJ. The Oestrid flies: biology, host-parasite relationships, impact and management. CABI Publishing; 2006.
[4] Slansky F Jr. Nutritional ecology of endoparasitic insects and related hosts: an overview. J Insect Physiol. 1993 Jul;39(7):577-91.
[5] Smith KGV. Manual of forensic entomology. 2nd ed. Natural History Museum; 1986.
[6] Zumpt F. Myiasis in man and animals in the Old World. Butterworths; 1965.
[7] James MT. The flies that cause myiasis in man. U.S. Department of Agriculture, Washington, D.C.; 1947.
[8] Papp L. Flies (Diptera) of Hungary. Vol 5: Oestridae. Hungarian Academy of Sciences; 1998.
