Botflies are parasitic insects whose larvae cause myiasis, the infestation of living tissue in mammals, including humans and cats. Common species include the Cuterebra botfly in North America and the Dermatobia hominis, or human botfly, prevalent in Central and South America. While a cat can host a botfly larva, the risk of directly contracting the parasite from your pet is extremely low. Cats are typically accidental hosts in the botfly lifecycle, meaning they are not an effective link for transmission to humans.
Understanding the Botfly Lifecycle
The adult botfly often resembles a bee and has non-functional mouthparts, living only a short time for reproduction. The female fly must deposit her eggs in a way that ensures the larvae reach a warm-blooded host. One common strategy is laying eggs near the burrows or runways of preferred hosts, typically rodents and rabbits.
Upon sensing the body heat of a passing mammal, the eggs hatch, and the tiny larvae quickly penetrate the host’s skin through an orifice, wound, or hair follicle. The human botfly, Dermatobia hominis, uses a more complex method: it captures a blood-feeding insect, such as a mosquito, and glues its eggs onto its abdomen. This insect acts as a phoretic vector, transferring the eggs to a host when it lands to feed. The host’s body heat then triggers the egg to hatch and the larva to burrow in.
Feline Botfly Infestation
Cats in North America are typically infested by Cuterebra species, which primarily parasitize rodents and lagomorphs. Infestation usually occurs when a cat investigates rodent nesting sites or areas where eggs have been deposited on vegetation. Cats are considered accidental hosts because the botfly is not specifically adapted to complete its lifecycle in a feline.
Once inside the cat, the larva migrates to a final subcutaneous location, usually around the head, neck, or face. Here, it creates a noticeable lump called a warble, a fibrous capsule within the tissue. The warble has a small breathing hole, or punctum, which the larva uses to breathe atmospheric air while it feeds and develops over several weeks.
The presence of the warble beneath the skin is the most common sign of infestation. If the larva migrates aberrantly, it can cause severe, though rare, issues, such as neurological damage if it travels toward the brain or spinal cord. Once mature, the larva exits the punctum, drops to the ground, and pupates into an adult fly, completing the cycle.
Zoonotic Transmission Risk to Humans
The probability of direct botfly transmission from a cat to a human is virtually non-existent, as the cat is a dead-end for the parasite’s immediate transfer. By the time an owner notices the infestation, the larva is already embedded within the cat’s subcutaneous tissue, sealed off in its warble. The larva is not capable of moving from the cat to a person.
Transmission would require direct contact with a newly hatched, migrating larva before it has burrowed into the cat, or contact with a mature larva actively exiting the cat, which is highly improbable. For humans, the primary risk of cutaneous myiasis, especially from D. hominis, is exposure in tropical and subtropical endemic areas where the phoretic vector is active. Human infection is therefore more of a geographic and environmental risk than a pet-related one.
In the rare instances of human infection in non-endemic areas, it is usually from an environmental source like direct contact with contaminated soil or vegetation, not from a domestic pet. The vast majority of human cases in the United States are diagnosed in travelers returning from Central or South America, confirming the geographic nature of the primary risk.
Recognizing and Treating Human Myiasis
Human cutaneous myiasis manifests as a painful, growing, boil-like lesion known as a furuncle. The lesion is often accompanied by a stinging or crawling sensation, sometimes described as movement within the lump. A tell-tale sign is the presence of a small central pore, the punctum, which allows the larva to breathe.
If a suspicious lesion is noticed, particularly after travel to an endemic region, it is imperative to seek professional medical attention immediately. Attempting “do-it-yourself” removal methods, such as squeezing the lump or covering the breathing hole with petroleum jelly, is strongly advised against. Squeezing can rupture the larva, leading to a severe inflammatory reaction, secondary bacterial infection, or potentially anaphylaxis from foreign material entering the bloodstream.
The standard medical procedure involves sterile, surgical extraction of the larva, often under local anesthesia. The doctor may gently enlarge the punctum or make a small incision to remove the entire larva intact using forceps. Proper, sterile removal is the only way to minimize the risk of complications and ensure the parasite is completely eliminated from the tissue.