Botflies, belonging to the fly family Oestridae, are insects whose larvae are obligate parasites within mammals, including humans and various animal species. The adult botfly is often large and bee-like but is harmless because it lacks functional mouthparts and does not feed. The danger lies entirely with its larval stage, known commonly as the bot, which develops inside the host’s tissues. While infestation is rarely fatal to a healthy host, it poses health hazards primarily through the condition called myiasis and the risk of secondary infections.
The Primary Danger: Understanding Myiasis
Myiasis is a parasitic infestation where fly larvae colonize and feed on the living or necrotic tissue of a host. The human botfly, Dermatobia hominis, typically uses a vector, such as a mosquito, to transfer its eggs onto the host’s skin. Once hatched, the larva penetrates the skin and establishes itself in the subcutaneous layer, where it develops for five to ten weeks.
As the larva grows, it creates a painful, boil-like lesion that discharges fluid and blood, maintaining a small central opening for breathing. The larva’s continuous movement causes intense, shooting pain, often described as a sensation of movement under the skin. Secondary bacterial infection is the most common complication, occurring when microorganisms enter the open wound.
Larvae can cause severe pathology if they migrate or infest sensitive areas. Larvae have been reported in the eyes, ears, or nasal passages, leading to ocular myiasis. The larva uses body spines and sclerotized mouthparts to anchor itself, making removal difficult without professional care.
Identifying Infestation Signs in Humans and Animals
The clinical presentation of botfly myiasis in humans is distinctive, manifesting as a furuncular lesion. This lesion is a firm, slow-growing nodule that resembles a boil or an epidermal cyst. The defining characteristic is a small, visible central opening, or punctum, through which the larva breathes.
Discharge from this pore is common, often including serosanguineous fluid (blood-tinged serum). Patients report local tenderness and intermittent sharp pain, especially when the larva moves. A medical professional may be able to see the posterior end of the larva within the opening, confirming the diagnosis.
In animals, physical signs vary depending on the botfly species and the host. Cattle and deer infested by warble flies (Hypoderma) develop “warbles,” which are noticeable lumps under the skin. Small mammals frequently host Cuterebra species, often presenting with large subcutaneous lumps around the head and neck.
Livestock, particularly horses and cattle, face consequences when heavily infested. Horse botflies (Gasterophilus species) primarily infest the digestive tract, leading to issues with nutrient absorption and gut damage. For cattle, large numbers of larvae can cause economic losses due to hide damage, reduced weight gain, and decreased milk production.
Treatment, Safe Removal, and Prevention
Professional intervention is necessary for safe removal of botfly larvae. Attempting to squeeze or extract the larva at home is discouraged because this can rupture the larval body. If the larva is crushed, it releases foreign proteins and bacteria into the wound, causing a severe inflammatory reaction, abscess formation, or secondary infection.
Non-surgical removal methods focus on occluding the breathing pore to asphyxiate the larva. Techniques involve applying petroleum jelly, heavy grease, or thick adhesive tape over the opening, forcing the larva to partially emerge to breathe. Once weakened, the larva can often be removed intact with forceps.
Surgical removal is sometimes necessary, especially if the larva is located in a sensitive area like the eye or scalp, or if occlusion methods fail. This procedure involves a small incision to enlarge the breathing hole, allowing the larva to be extracted completely. Following removal, the wound is treated with an antibiotic ointment to prevent secondary bacterial infection.
Prevention for humans focuses on avoiding exposure in endemic tropical regions by using insect repellent and protective clothing. For animals, prevention involves fly control measures and the use of systemic antiparasitic medications, such as ivermectin, which kill the larvae internally. Regular inspection and prompt treatment of suspected lesions are crucial to limit damage.