It seems like something out of a science fiction movie: a parasitic larva that can live and mature under the skin of a mammal until it's ready to jump out and complete its life cycle. It's called Cuterebra, and it's the larva of a botfly. Cats, dogs, ferrets, and even humans can be affected by botfly larva. Removing the unwelcome larva is the key to treating this relatively common condition.
What is Cuterebra?
Cuterebra is the scientific name for a type of botfly that causes a parasitic infection called cuterebriasis. Cuterebriasis occurs in cats when the larva of the fly enters the cat's body. Cuterebra lesions are sometimes called "warbles."
Cuterebra are large flies that lay their eggs near the nests and burrows of small mammals like rodents and rabbits. When a host animal walks by, the eggs can become attached and hatch in response to the animal's body heat. The newly hatched larvae typically enter the animal's body via the mouth or nose during grooming or through open wounds on the skin. The larvae migrate and incubate in the host's body, getting oxygen through a small, round breathing pore on the skin. After about 30 days, the larvae mature and fall off the host to pupate in the soil until they develop into adult flies.
Cats are not ideal hosts for Cuterebra, but may become inadvertently infected after coming into contact with botfly eggs. Lesions typically occur near the head and neck but can appear anywhere on the body. Cuterebra larvae look like short, fat worms that are usually up to an inch long. They are typically gray or beige in color.
Signs of Cuterebra in Cats
Cuterebra lesions typically appear as a swollen area under the skin with a small hole in the center. Lesions are often seen near the head or neck but they can be found anywhere on the cat's body. They are generally non-painful unless they invade sensitive tissues. However, the swelling but may be bothersome to the cat and cause increased grooming. Owners may discover matted hair over the larva's breathing hole.
In rare but serious cases, Cuterebra larvae can migrate to the delicate tissues of the nasal cavities, head, brain, eyelids, and pharynx. Cerebrospinal cuterebriasis occurs when a lesion affects the central nervous system, leading to neurological problems like seizures, circling, unusual behavior, and blindness. It is believed that Cuterebra infections can cause a neurological condition called feline ischemic encephalopathy.
Cuterebra lesions are generally not visible until the larva becomes large enough to cause a lump or swelling. In some cases, the larva will mature and leave the cat's body before it is ever seen. A bacterial infection can occur in the remaining skin lesion and lead to an abscess.
Contact your veterinarian if you notice swelling anywhere on your cat's body. Treatment may be needed even if the larva has left the cat.
Causes of Cuterebra in Cats
Cats are considered "accidental" hosts of Cuterebra. They most often come into contact with botfly eggs while outdoors hunting and exploring the burrows of small wild animals. Therefore, outdoor cats are far more likely to develop cuterebriasis than indoor cats.
Cuterebra is commonly found all over the Americas. In North America, infestations occur most commonly in the summer and fall.
Humans cannot get Cuterebra infections from their cats, but it is possible to develop a lesion after coming into direct contact with botfly eggs.
Cuterebra lesions are treated by first removing the fly larva from the body, if present. Your veterinarian may recommend sedation for your cat in order to remove the larva and clean the wound properly.
Larva removal is fairly straightforward, but it can be tricky. The larva should be removed in one piece to avoid contamination. The veterinarian will enlarge the breathing hole, then grasp the larva with forceps. It can be easier to use petroleum jelly to block the air hole before removing the larva.
After the larva has been completely removed, the remaining wound is cleaned and flushed out. Unhealthy tissue is debrided (cut away) to promote healing. The affected cat may need treatment with antibiotics. Pain medication and anti-inflammatory drugs may be prescribed to provide comfort if the wound is very irritated.
Recovery is typically fast as long as the cat is unable to groom the affected area during healing. Your cat may need to wear an e-collar (the "cone of shame") until the wound has healed.
How to Prevent Cuterebra in Cats
The best way to protect cats from Cuterebra infections is to keep them indoors at all times. Outdoor cats often hunt small mammals and may come into contact with Cuterebra larvae. If your cat does go outdoors, check him regularly for signs of swelling. Contact your vet if you notice anything abnormal.
“Cuterebra Infestation in Dogs and Cats.” Merckvetmanual.Com, https://www.merckvetmanual.com/integumentary-system/cuterebra-infestation-in-dogs-and-cats/cuterebra-infestation-in-dogs-and-cats.
James, Fiona M. K., and Roberto Poma. “Neurological Manifestations of Feline Cuterebriasis.” The Canadian Veterinary Journal. La Revue Veterinaire Canadienne, vol. 51, no. 2, 2010, pp. 213–215