Myiasis is the infestation of human and animal tissue by the larval or pupal stages of two-winged true flies (Diptera) or maggots. Myiasis is widespread in the tropics and subtropics of Africa and the Americas, but less prevalent elsewhere. The infestation can involve numerous species, and clinical presentations include nodules, ulcers, creeping eruption, and wound contamination. The goal of therapy is complete larvae removal and preventing future infestation.
In the early 20th century, myiasis was a major public health and economic problem affecting livestock and humans. Since then, the incidence has decreased due to improvements in hygiene and wound care. Reports of human infection continue today, including nosocomial outbreaks. The mechanism of transmission of fly larvae to human hosts differs among the many species of flies; however, cutaneous invasion occurs in all species by the larvae burrowing into the skin. The management goal is to prevent exposure to larvae.
Myiasis may be acquired during travel to Central and South America and parts of Africa. Individuals traveling to rural areas should be covered at all times with long-sleeved garments and hats. At night, sleeping under a mosquito net and utilizing insect repellents are useful, as the mechanical vectors for certain larvae are blood-sucking arthropods such as mosquitos. Certain flies deposit their eggs on clothing, so clothing should be dried and hot-ironed to kill any eggs. Other flies deposit their eggs in soil, where larvae hatch and may penetrate the barefoot skin, which can be prevented by appropriate footware.
To prevent wound myiasis, simple antisepsis is usually sufficient. Wounds should be cleaned and irrigated and covered, with proper dressings. Patients with wounds should never sleep outside, and in an indoor or hospital environment, windows should remain closed.
Once infestation has occurred, therapy consists of removal of all larvae with minimal trauma to the organisms. Occlusion deprives the larva of oxygen and induces movement in search of air, allowing manual removal. When few organisms are present, infiltration of the area with lidocaine and surgical removal is adequate. Care must be taken to extract the larvae whole; otherwise, a considerable foreign body reaction may ensue. A secondary pyogenic infection should be treated with appropriate antibiotics. Supplemental treatments, such as isopropyl alcohol, Dakin’s solution, iodine, or hydrogen peroxide are needed for treatment of wound myiasis.
The fly larvae should be extracted whole and specific identification should be attempted. Each larva may molt and have several instars, each with a slightly different morphology, complicating identification. The adult fly should be identified, if possible. Consultation with an entomologist in difficult cases is helpful. Scanning electron microscopy and molecular studies by multiplex polymerase chain reaction (PCR) may aid identification.