What is nastier than a maggot wriggling around on a piece of meat? Read on and you’ll find out….
History of Present Illness
A 32 year old otherwise healthy female presents to the Emergency Department with a painful red lump on just above her left knee that she has had for about a month. Initially she thought it was just a mosquito bite, but it has gradually grown in size, and is now occasionally draining small amounts of bloody pus. She saw her doctor who placed her on Keflex a week earlier but the condition had only worsened. She also complains of occasional stabbing pains emanating from the boil, which last a minute or two and are particularly severe at night.
- Social History: Occasional Marijuana
- Meds: Oral contraceptives, Keflex 500 mg QID
- Allergies: None
After you remark about her Billabong T-shirt she mentions that she had been in Managua, Nicaragua for two weeks volunteering at a medical clinic, then spent a guilt-free week surfing Asuchillo’s hollow lefts. She’s been back home in Rhode Island for two weeks.
- Physical Exam:
Her leg looked like this: 
- Vital signs: B.P. 110/55, T 37o C, Pulse 88, R.R. 12
On physical exam the patient is in no apparent distress. She is well developed and well nourished, and the only significant abnormality is the lesion above that has some yellow drainage. She tells you she feels like something is moving under her skin – another crazy ER patient!
You figure the patient has a small abscess, likely a MRSA infection, and prepare for an I&D, when the nurse, who is from Costa Rica, pulls you aside and tells you the patient has a subcutaneous Botfly larvae. You place an ultrasound probe on the wound, and to your amazement you see what appears to be a cylindrical object moving just under the skin. You ponder how to remove this nasty parasite.
Take the Botfly Removal Quiz:
(Answer at the end of the article)
- A. Give the patient 1 tablet of the deworming agent Mebendazole.
- B. Place a piece of raw meat on the patients skin to lure the bugger out (as your nurse suggests).
- C. Cover the wound with Vaseline and duct tape to choke it out.
- D. Squeeze both sides of the lesion so the maggot pops out (like a pimple).
Discussion
Furuncular myiasis is caused by the larvae of the human botfly Dermatobium Hominis whose range extends from the tropical lowlands of Southern Mexico to South America. Botfly infestation is not uncommon among surfers returning from (or residing in) endemic areas, but it is commonly misdiagnosed as an abscess, sebaceous cyst, or zoster by physicians from North America and Europe who are often unfamiliar with this malady.
Source: CDC
The lifecycle of the Botfly is quite unique. The adult fly only lives about 10 days, has no ability to feed, and rarely bites its human host. Instead, the female fly captures a mosquito mid-flight and deposits her eggs on the mosquito, which then serves as an intermediate vector, a process termed phoresis. As the mosquito lands on a human to feed, the eggs are triggered by warmth to hatch into minute larvae, which penetrate the host’s skin within minutes, often entering through the mosquito bite. The larvae feed on subcutaneous tissue and sebum, going through two additional molts, gradually increasing in size. As the larva grows it periodically excretes its waste though a central pore (visible in the photo above), which also serves as a breathing hole. After a few weeks the larva becomes more active in its burrow and the infested victim experiences episodes of stabbing pains and often senses movement under the skin.
Each breathing hole is associated with a single larva, but it is not unusual for an individual to harbor several larvae in adjacent furuncles, particularly in the scalp or back. Larvae remain anchored by rows of circumferential upward-facing barbs and grow to a size of approximately 2.5cm (1 inch). If untreated, after approximately 2 months the larva will pupate in the form of a black casing, and fall to the ground where it will later hatch a month later into an adult fly. Due to physical and psychological discomfort, few (if any) people are willing to allow the larva to pupate once a diagnosis has been established – they want the evil maggot out NOW.
Botfly larvae. Note tiny rows of anchoring barbs. Red arrow points to mouth, which is oriented deep to host’s skin. (Photo: Wikipedia)
The medical literature describes a number of techniques for botfly larva removal and there are innumerable folk remedies as well. Because the larvae’s barbs give them a tenacious grip within their burrows, trying to expand the breathing hole (often hidden under a crust of secretions) and pull out a live maggot intact is nearly impossible. Inevitably fragments of the worm are left behind, which can result in infection.
The most successful approach is to suffocate the learvae by forming an occlusive barrier over it’s breathing hole using a layer of Vaseline-impregnated gauze covered by tape. It may take up to 24 hours for the larva to die, and it often wriggles around in its death throes, causing added discomfort to the host. In an attempt to breathe, larvae may protrude from their burrows and become visible. Once dead, or nearly so, tweezers can be used to slowly and gently extract the partially exposed parasite. Beware that tugging too quickly can tear the worm apart, leaving behind remnants that may be difficult to extract.
See videos: Botfly removal 1, Botfly removal 2
After successful extraction, the worm-hole should be irrigated, and a topical antibiotic ointment can be applied. Although the area may appear to be infected, redness and swelling are generally secondary to a foreign body reaction as opposed to a bacterial infection, and oral antibiotics are generally not indicated. There is some evidence that larvae excrete antimicrobial substances (they don’t want an infected burrow), which explains why the lesions are sterile, despite the presence of an open wound.
A more recently described technique involves the use of a “Sawyer Venom Extractor” a syringe-like suction mechanism originally designed to remove venom from a snake bite (little evidence supports its use for venom removal). First the larva is suffocated as above, then the suction device is placed on the skin and the plunger is retracted creating a vacuum in the syringe and sucking out the larva.
Lastly, after suffocation, the larva can be removed by applying manual pressure to either side of the wound, forcefully popping the larva out – resulting in gasps and applause from any onlookers. This latter technique is often employed in Central America where botfly infestation is common.
Preventing cutaneous myiasis is all about preventing mosquito bites – which is a good idea anyway, given that mosquitos from these regions may also carry the risk of transmitting Malaria, Dengue fever, and other diseases. Unfortunately, many species of mosquitos feed at dawn and dusk – primetime for most surfers – as well as at night when you are likely to be asleep. A thorough dissertation on mosquito prevention is beyond the scope of this case report, but suffice it to say that DEET and Picaridin (made from the pepper plant) are the most effective repellents and last 6 – 8 hours on dry skin. When travelling to mosquito infested locales, long sleeved clothing sprayed with Permethrin should be worn when up and about, and when it comes time to sleep Permethrin-impregnated sleeping nets are the safest bet.
Summary
The diagnosis of Botfly infestation should be considered in travellers returning from Central and South America with furuncular lesions. The presence of a central breathing hole, or visualization with ultrasound confirms the diagnosis. Removal involves placing an occlusive dressing over the central pore for several hours, and gradual extraction of the larva.
(Answer: C)
References
- West, JK. Simple and effective field extraction of human botfly, Dermatobia hominis, using a venom extractor” Wilderness Environ Med. 2013 Mar;24(1):17-22
- Mahal JJ, Sperling JD. Furuncular myiasis from Dermatobium hominia: a case of human botfly infestation J Emerg Med. 2012 Oct;43(4):618-21
- Mikhail M, Smith BL. What’s eating you? Human Botfly (Dermatobia hominis) Cutis. 2009 Aug;84(2):81-3.