Human bot fly

The genus Dermatobia contains only one species, D. hominis, the only species of bot fly that attacks humans (in addition to other primates). It is also known as the torsalo. In this species the fly's eggs are vectored by mosquitoes and muscoid flies; the female Dermatobia captures the mosquito and attaches its eggs to the body of it, then releases it. The eggs hatch either while the mosquito is feeding and the larvae may use the mosquito bite area as the entry point, or simply drop off the muscoid fly when it lands on the skin. They develop inside the subcutaneous layers, and after approximately 8 weeks they drop out to pupate for at least a week, typically in the soil. The adults are small gray flies resembling a blowfly.

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This species is native to the New World tropics, though it is not abundant enough (nor harmful enough) to ever attain true pest status. Since the fly larvae can only survive the entire eight week development if the wound does not become infected, it is rare for patients to experience infections, unless they kill the larva without removing it completely (below). It is even possible that the fly larva may itself produce antibiotic secretions that help prevent infection while it is feeding.

Remedies

The botfly maggot cannot be removed easily whilst alive due to the strong, hooked spines that run in circular rings around the midsection of its body. However, various solutions have been suggested:

• Immediate contact with larvae can be remedied with alcohol.

• Recently, many physicians have discovered that venom extractor syringes can remove larvae with ease at any stage of growth. As these devices are a common component of first-aid kits to deal with snakebites, this is an effective and easily accessible solution.

• Duct tape can kill the larvae by cutting off their air supply.

• Some people have reported success simply by careful application of pressure - but this approach runs a very high risk of killing the larva in situ, leading to infection. One medical treatment is to suffocate the grub by sealing off the air hole found in the surrounding blister. This can be done with petroleum jelly or a similar substance. This forces the grub to expose itself temporarily (to clear the spiracles), making it easier to remove, though it is still risky if the larva does not come completely out of the wound, and therefore is not a simple matter to perform without killing the larva and causing infection. Most commonly, people will snap off the tail of the larva, leaving the portion with the hooks still embedded.

• A similar "cure" (which is really more of a folk remedy) is to put meat over the affected area while the flies are in their larval stage, thereby cutting off the parasites' air supply. The grubs should then burrow through the meat to gain access to oxygen, at which point the meat may be removed with the larvae trapped inside. It is unclear, however, whether this is generally effective, and controlled experiments have not been done to determine precisely which "home-grown" method of extraction is safest, most effective, or easiest. Surgical removal is an option, of course, but could be costly for those without access to affordable healthcare.

• In general, then, simply allowing the larva to develop and leave the body on its own is the safest and least risky course of action, though few people are willing to wait that long, especially if the larva is lodged in an uncomfortable or unsightly location. The degree of discomfort experienced does seem to be entirely dependent on where the larva is located, related to how sensitive the surrounding tissue is.

See also

• Myiasis