Humans can get botfly infestations, primarily from the species known as the human botfly, Dermatobia hominis. A botfly is a type of fly whose larvae are internal parasites of mammals. While various botfly species exist, Dermatobia hominis is the only one that routinely infests humans. This condition, known as myiasis, involves the infestation of host tissue by fly larvae.
How Botfly Infestation Occurs
The human botfly, Dermatobia hominis, employs a unique and indirect method to infest humans, differing from flies that lay eggs directly on a host. The adult female botfly captures another arthropod, typically a mosquito or other fly, or even a tick, in mid-air. She then attaches her eggs, usually between 10 to 50, to the underside of this vector insect’s abdomen.
After the eggs are secured, the female botfly releases the vector insect. When this carrier insect lands on a human or other warm-blooded animal to feed or rest, the host’s body heat triggers the botfly eggs to hatch. The newly hatched larvae then penetrate the skin of the human host.
Larvae typically enter the skin through hair follicles, small cuts, or the bite wound created by the vector insect. Once inside, they burrow into the subcutaneous layer, which is the tissue just beneath the skin. The larvae reside there, feeding on the host’s soft tissue and developing for a period, usually ranging from five to ten weeks.
Recognizing a Botfly Infestation
A botfly infestation often presents with distinct signs and symptoms that can help in its recognition. The most characteristic sign is a raised, boil-like lesion on the skin, often referred to as a “warble.” This lesion typically has a small central opening, which serves as a breathing hole for the developing larva. Redness and slight swelling may accompany the lesion.
Common locations for these lesions include exposed skin areas, such as the scalp, face, arms, and legs. Individuals may experience sensations such as itching, persistent pain, or a feeling of movement directly beneath the skin. A yellowish or bloody fluid might also be discharged from the central opening. These symptoms can develop over several days or weeks after the initial larval penetration.
Treatment and Removal
Professional medical attention is important for the safe and effective removal of botfly larvae. Self-removal is generally not recommended due to several risks, including incomplete extraction, potential rupture of the larva, or secondary bacterial infections. A ruptured larva can lead to a more intense inflammatory reaction or an allergic response.
Medical professionals typically employ specific techniques for extraction. One common method involves occluding the central breathing hole of the lesion with a substance like petroleum jelly or other medical-grade adhesive. This deprives the larva of oxygen, causing it to emerge partially from the skin in search of air. Once sufficiently exposed, it can be grasped and carefully extracted, often with forceps. In some cases, a small surgical incision might be necessary to remove the larva, especially if deeply embedded or other methods are unsuccessful.
Prevention Strategies
Preventing botfly infestation involves practical measures, especially for individuals traveling to or residing in areas where the human botfly is common, such as parts of Central and South America. Wearing protective clothing, including long-sleeved shirts and long pants, can reduce exposed skin surfaces. Tucking pants into socks provides additional coverage.
Using insect repellents containing active ingredients like DEET or picaridin on exposed skin and clothing is a useful deterrent. Applying permethrin to clothing and gear offers further protection. Limiting outdoor activities during peak insect hours, typically dawn and dusk, can help reduce exposure. Sleeping under permethrin-treated mosquito netting provides a barrier against carrier insects during the night.