The short answer to whether a human can be infested by a “wolf worm” is yes, though such cases are considered extremely rare and accidental. This parasite is not a true worm but the larval stage of a type of botfly, primarily from the genus Cuterebra. The resulting condition is a form of myiasis, which is the infestation of a living mammal by fly larvae. While the parasite is typically associated with wildlife, humans who spend time outdoors in endemic areas can inadvertently become a host.
Defining the Organism Known as the Wolf Worm
The organism commonly called a wolf worm is the larva of the botfly, primarily from the genus Cuterebra. These insects are large, bee-like flies, and the species most often involved in North American cases are obligate parasites of small mammals. Natural hosts include rodents like mice and squirrels, and lagomorphs such as rabbits. The life cycle begins when the adult female fly lays her eggs near the entrance of a host’s burrow or along a rodent run.
The eggs are often deposited on grass, twigs, or wood chips, and they are stimulated to hatch by the body heat of a passing mammal. The tiny, newly hatched larva, known as the first-instar, then crawls onto the host’s fur. To complete its development, it must migrate internally to a subcutaneous (under the skin) location. Once settled, the larva develops into a large, spiny form, creating a characteristic swollen lump, or “warble,” with a breathing hole in the host’s skin. After about a month, the mature larva exits the host and drops to the ground to pupate, eventually emerging as an adult fly.
Accidental Human Infestation
Humans become involved in this lifecycle accidentally, as we are not the intended host species for Cuterebra. The most common route of infection involves contact with the environment where the fly eggs have been laid, such as areas near rabbit or rodent burrows. A person may inadvertently brush against contaminated vegetation, causing the larva to hatch and latch onto the skin. The larvae gain entry into the human body through intact skin, a small abrasion, or by entering a natural opening.
The larvae often enter through the mucous membranes of the face, such as the nose, mouth, or eyes, or through a break in the skin. Since humans are atypical hosts, the larvae frequently exhibit aberrant migration patterns. While most cases present as furuncular myiasis (a boil-like lesion in the skin), some larvae migrate to other areas. This includes the eyes (ophthalmomyiasis), the nasal passages, or even the central nervous system, which can result in serious complications. Infestations are most frequently reported during the late summer and early fall months, aligning with the peak activity period of the adult botflies.
Clinical Presentation and Identification
The most common clinical presentation is furuncular myiasis, appearing as a firm, painful lump under the skin. This lesion typically resembles a bacterial boil or an infected cyst, often leading to misdiagnosis. A distinctive feature is a small, central opening, which the larva uses as a breathing pore. Clear to bloody fluid may drain from this hole, and some patients report a sensation of movement or a stabbing pain within the lesion.
The mature larva can reach up to 2 centimeters in length. Diagnosis is generally achieved through a physical examination, with the physician observing the characteristic lesion and the central breathing pore. In some instances, the dark, heavily spined tail end of the larva may be visible through the opening. Patient history, especially recent outdoor activity or contact with pets, is an important clue to distinguishing this condition from a simple bacterial infection.
Treatment and Prevention
Treatment involves the professional removal of the entire larva. Surgical extraction is the most common method, often involving a small incision to enlarge the breathing pore and allow for the complete removal of the parasite using specialized forceps. It is strongly advised not to attempt to squeeze or rupture the larva during removal. Rupturing the larva can release internal contents into the host’s tissue, potentially triggering a severe inflammatory response, a foreign body reaction, or anaphylactic shock.
After the larva is extracted, the wound site is thoroughly cleaned and allowed to heal naturally. In some cases, oral medications like ivermectin may be used to help kill the larva or reduce inflammation, particularly in cases of deeper or internal migration. Prevention relies on minimizing contact with areas where the botflies are active. Simple measures include avoiding lying directly on the ground in rural or wooded areas and being cautious around known rodent or rabbit habitats.