Cuterebra are large flies whose larvae (small worms) infest the skin of rodents, squirrels, rabbits, dogs and cats. The adult fly is seldom seen. The female deposits eggs near the nests of rabbits or rodents. The larva, which look like small worms, hatch from the eggs when exposed to the heat of the nearby animal. After hatching, the larva migrate through the nose, mouth or skin wound of the rabbit or rodent and burrow under the skin. A cyst, with a hole in the center through which the larva's head can be seen, forms around the larva. Cuterebra larva can grow up to 1 inch long and ½ inch in diameter. After about a month, the mature larva emerges from the cyst and burrows into the soil to pupate. After a variable pupation period, the adult fly emerges.
Cats can acquire cuterebra larva after curious investigations of a rodent or rabbit den. By investigating the area, the cat may come in contact with cuterebra eggs or larva. Migration in the body occurs in the same way as in the rabbit or rodent. After migrating to the skin, the larva will form a breathing hole where pus drains from the skin to the outside.
Most cuterebra larvae are found on the head and neck of cats. Sometimes, the larvae migrate abnormally and end up traveling through the brain. This results in fatal brain and nervous system abnormalities, such as seizures. Typically, one larva is found per breathing hole.
What to Watch For Lump or mass under the skin often found on the head or neck
Open area in center of lesion
Diagnosis of cuterebra larva is based on physical exam findings and visualization of the larva.
Removal of the cuterebra larva can sometimes result in serious side effects. For this reason, removal by a veterinarian is strongly recommended. The larva must be removed in one piece. If the larval body is ruptured during the extraction process, the cat may develop serious complications such as severe allergic reactions or anaphylaxis. For this reason, the breathing hole is typically enlarged by using surgical scissors or a scalpel blade, in the presence of local anesthesia. After the hole is enlarged, the larva are safely removed with a forceps or hemostat, and the area is flushed and cleaned with disinfectant. Antibiotics may be prescribed.
Home Care and Prevention
Home removal of cuterebra larva is not recommended due to the potential for serious reactions. After removal, the wound should be kept clean and allowed to heal.
The best way to prevent cuterebra larval migration is to limit access to rabbit and wild rodent nests or burrows by keeping your cat indoors. If this is not possible, frequent checks of your cat's skin may help remove cuterebra larva early in their development.