Maggots due to Cuterebra fly larvae is most commonly seen within the skin of wild and domestic animals, and rarely in humans. Adult Cuterebra flies are large and bee-like, and neither bite nor feed. They are not directly attracted to a host species but the females lay their eggs along rabbit runs and near rodent burrows. If an animal brushes up against the eggs they hatch instantaneously. Larvae enter the body via natural body openings, by skin penetration, or by ingestion as the animal grooms contaminated fur. Dogs may become infested as they pass through contaminated areas. The natural hosts are usually rabbits and other rodents. Rabbit Cuterebra are less host specific and usually affect cats and dogs. In these abnormal hosts the larvae have been observed in the brain, causing neurological clinical signs. Clinical abnormalities noted in affected animals are progressive and most commonly consist of depression, blindness, and behavior changes.
Lesions are usually noted in late summer or fall. Larvae produce a boil of 1 to 2 cm in diameter, which develops a pore. Nodules are typically localized to the head, neck and trunk. Because dogs and cats are abnormal hosts, the larvae may undergo unusual migrations to the brain, pharynx, nostrils, and eyelids. The hair is often matted and the skin is swollen. The boil may be painful and discharge pus.
Definitive diagnosis is made when the larvae are found. Larva is dark-brown to black and has spines or spinules. Suspected boils should be explored carefully by a veterinarian. The boil should not be squeezed because this may rupture the larva and lead to secondary infection or severe allergic reaction. The pore or fistula is enlarged and larvae removed with a mosquito forceps. If larva is not removed intact, the retained parts may cause allergic or irritant reactions. The wounds must be kept clean. Expect the healing to be slow.
- Scott, Miller, Griffin: Parasitic Skin Diseases. Small Animal Dermatology, 5th ed., W.B. Saunders, Philadelphia, PA, 1995