Larvae are the immature form of insects, such as flies and beetles, primarily designed for feeding and growth. When these larval forms, commonly known as maggots, infest the living tissue or body cavities of a mammal, the condition becomes a specific health concern. The severity of the resulting condition depends on the specific fly species and the location of the developing organisms within the host.
Myiasis: The Medical Infestation
The medical and veterinary term for the infestation of living vertebrates by fly larvae is Myiasis. This condition is caused by the developing larvae of various two-winged fly species (order Diptera), which feed on the host’s tissue or fluids. Myiasis is categorized based on the fly’s necessity to use a living host to complete its life cycle. Obligate myiasis occurs when the fly species, such as the New World screwworm, must develop in a living host to survive. Facultative myiasis involves flies that usually lay eggs in decaying matter but can opportunistically infest a living host, particularly one with pre-existing wounds or poor hygiene. Accidental myiasis happens when fly eggs or larvae are accidentally ingested or deposited, leading to temporary internal infestation.
How Larval Infestation Occurs
Infestation begins when a gravid female fly deposits its eggs or larvae near or directly onto a susceptible host. Flies such as blowflies and screwworms are attracted to open wounds, ulcers, or areas soiled with bodily fluids. They lay their eggs so the hatched larvae can feed on the tissue of the wound. Other species, like the human botfly (Dermatobia hominis), use phoresis, where the female attaches eggs to a carrier insect, such as a mosquito. When the carrier lands on a mammal, the warmth causes the eggs to hatch, and the larvae immediately penetrate the skin. The tumbu fly (Cordylobia anthropophaga) typically lays its eggs on soil or damp clothing, from which the larvae hatch and burrow into the host’s unbroken skin upon contact. The larvae feed on the host’s tissue until they are ready to emerge.
Recognizing Symptoms and Associated Health Risks
Symptoms vary based on the affected body site and the type of larva present. Cutaneous myiasis, which affects the skin, often presents as a furuncle, or a boil-like lesion, with a central opening for the larva to breathe. Patients report localized pain, itching, and a distinctive sensation of movement beneath the skin. Wound myiasis involves the visible presence of maggots in an open wound, often accompanied by a foul-smelling discharge and bleeding. The most significant health risk is massive tissue destruction as the larvae feed and burrow deeper. This damage makes the site highly susceptible to secondary bacterial infections, such as cellulitis, which can lead to systemic illness. Intestinal and urogenital myiasis occur when larvae are ingested or enter through body openings, causing symptoms like abdominal pain, vomiting, or irritation of the urinary tract. Lesions from migratory myiasis create creeping, itchy tracts under the skin as the organism moves through the subcutaneous tissue.
Treatment and Prevention Strategies
Professional medical intervention is necessary for the safe removal and management of the infestation. For cutaneous forms, treatment often involves non-surgical methods such as occlusion, where a substance like petroleum jelly is placed over the breathing pore. This deprives the larva of oxygen, forcing it to emerge for manual extraction with forceps. Surgical removal under local anesthesia may be required for deeply embedded larvae or when the larva has died inside the lesion. Careful excision is necessary to avoid leaving behind fragments that can trigger a severe inflammatory reaction. Wound myiasis is treated by irrigating the wound to flush out organisms, followed by manual debridement to remove all larvae and necrotic tissue. Pharmacological options, such as oral or topical ivermectin, may be used to kill or immobilize the larvae before extraction. Prevention focuses on strict hygiene, proper care of open wounds, and reducing contact with flies in endemic regions. Simple measures, like ironing line-dried clothes in areas where tumbu flies are present, can destroy any eggs deposited on the fabric.