The human botfly, Dermatobia hominis, is an insect species native to tropical and subtropical regions of the Americas. Infestation by the larval stage of this fly causes cutaneous myiasis, where the larva develops beneath the skin. The female botfly typically lays its eggs on a carrier insect, such as a mosquito, which then deposits the eggs onto a host’s skin. The newly hatched larva penetrates the skin, creating a subcutaneous burrow where it feeds and grows for approximately five to ten weeks. Removal is necessary because the larva’s presence can cause pain, significant tissue damage, and the risk of secondary bacterial infection if it is injured during attempted extraction.
Identifying a Botfly Infestation
The first sign of infestation is often a small, red, raised bump on the skin, which may initially resemble an insect bite or a developing boil. This lesion, sometimes called a “warble,” gradually enlarges over several weeks as the larva grows inside. A characteristic feature is the punctum, a small, open breathing hole at the center of the lesion through which the larva’s posterior end is exposed to the air.
The site of infestation typically discharges a thin fluid, as the larva must keep the opening clear for respiration. Patients often report localized pain, which can intensify into sharp, shooting pains when the larva shifts position. A subtle but distinctive symptom is the sensation of movement or tingling felt beneath the skin, caused by the larva burrowing or moving its body spines.
Safe Non-Surgical Extraction Techniques
The principle behind non-surgical removal is to force the larva to emerge by depriving it of air. Since the larva requires the punctum to breathe, covering this opening with an occlusive substance prompts it to move toward the surface to seek oxygen. Petroleum jelly, thick adhesive tape, or a piece of raw meat like bacon can be used to completely seal the breathing hole.
Once the punctum is covered, the larva typically begins to emerge after several hours, though occlusion may be left in place for up to 24 hours. As the larva partially emerges, it can be gently grasped at its head end with forceps or tweezers and removed with a steady pull. A commercial venom extractor, which uses negative pressure, has also been successfully used to painlessly draw the larva out intact after the area is occluded.
Avoid forcefully squeezing the lesion in an attempt to expel the larva. The larva is covered in backward-pointing spines, which anchor it firmly inside the host tissue. Squeezing significantly increases the risk of rupturing the larva, which releases foreign proteins and toxic substances into the tissue. This rupture can lead to a severe allergic reaction (anaphylaxis) or a significant secondary infection, complicating subsequent medical treatment.
Surgical Removal and Medical Necessity
Professional medical intervention is recommended when non-surgical methods fail after a day, or if the lesion is located near a sensitive anatomical structure. Infestations near the eyes, joints, mouth, or genitalia require immediate surgical management due to the high risk of functional impairment or severe complication. Signs of an advanced secondary bacterial infection, such as increased redness, fever, or excessive pus discharge, also necessitate professional removal and antibiotic treatment.
The standard medical procedure involves using local anesthesia to numb the area, which helps to immobilize the larva. The physician then uses a scalpel or a small punch biopsy tool to carefully enlarge the punctum, creating a wider opening. Once the opening is sufficient, the intact larva is extracted using specialized forceps or hemostats.
Surgical removal allows for the precise extraction of the entire larva, mitigating the risk of leaving behind fragments. This is important because incomplete extraction is the primary cause of severe secondary infection. An untrained person attempting removal risks leaving behind parts of the larva, which can lead to chronic inflammation, abscess formation, or a severe immune response.
Post-Removal Care and Prevention
Immediately following the extraction, the resulting cavity must be thoroughly cleaned to prevent bacterial colonization. The wound is typically flushed with a sterile saline solution or an antiseptic agent to remove residual debris or potential pathogens. The site should then be dressed with a sterile bandage, and a topical antibiotic ointment may be prescribed to reduce the risk of secondary infection.
Monitor the wound closely over the next few days for signs of developing infection, including increasing swelling, spreading redness, pus discharge, or persistent pain. If the extraction involved an open or ragged wound, or if the patient’s tetanus vaccination status is unknown or outdated, a tetanus prophylaxis is often administered. Most wounds from an extracted botfly larva heal naturally within a couple of weeks.
For travelers to endemic tropical regions, preventive measures can significantly reduce the risk of infestation. Using insect repellent containing DEET or picaridin on exposed skin provides a chemical barrier against carrier insects. Wearing long sleeves and long pants, especially during peak insect activity times, offers a physical barrier. Ironing clothing that has been line-dried outdoors can kill any botfly eggs that may have been deposited on the fabric.