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Clinical Summary

Myiasis is the invasion of living human or animal tissue by maggots, the larvae of flies. Infection is most commonly subcutaneous, but may be seen in wounds and body cavities. The human botfly (Dermatobia hominis) is a major cause of furuncular myiasis in the New World; mosquitoes courier eggs to the host. A papule develops as the larvae feed, followed by a pruritic furuncle, often with drainage from a central punctum. After maturation, the larva emerges and falls to the ground, where it pupates in the soil and evolves into an adult fly.

The tumbu fly, found in Africa, also causes furuncular myiasis and is spread from eggs deposited in soil, sand, or clothes. Screwworm species are found in the Old and New Worlds. These worms are notorious for direct deposition of eggs after flying into the nasal cavity, leading to nasal cavity myiasis. Feeding maggots can cause extensive tissue damage. Wound myiasis, caused by numerous fly species, is seen in open sores and gangrenous tissues. Wearing protective clothing, using insect repellant, and covering wounds are preventative measures.

Management and Disposition

Lidocaine injection at the lesion base, or application of suffocating occlusive substances such as Vaseline, may cause the larva to surface and facilitate removal in furuncular myiasis. Incisional extraction is challenging due to the larva’s tapered shape and many rows of spines and hooks that it uses to grip tissue. Wound myiasis is treated with thorough debridement. Secondary infection is the only indication for antibiotics; it is uncommon due to bacteriostatic activity in the gut of the larvae, but may occur by leaving portions of them after removal.

FIGURE 21.59

Myiasis. Preserved specimens of D hominis. (Photo contributors: Rob Greidanus, MD, and Universidad Peruana Cayetano Heredia, Lima, Peru.)

Pearls

  1. Patients with lesions may have the sensation of something moving under the skin.

  2. Myiasis is self-limiting and usually not harmful, but it does cause psychological distress to the host, especially when the larvae surface. Although rare, deaths from meningitis have occurred after tissue penetration from infection in the eye, nose, or ear canal.

  3. Screwworms are major pests of livestock. A sterile male release program has eliminated the screwworm from the United States.

  4. Some feel that fly maggots are a useful method of wound debridement. Packets of fly maggots have been commercially developed for this purpose.

FIGURE 21.60

Wound Myiasis. Wound myiasis in an elderly patient following dressing removal. (Photo contributor: Seth W. Wright, MD.)

FIGURE 21.61

Myiasis. Wound on the arm of a woman who had visited the Amazon jungle. A D hominis larva was extracted from the wound. (Photo contributors: Seth W. Wright, MD, and Universidad Peruana Cayetano ...

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