Cuterebrosis in Cats
Botflies, flies that are of the genus Cuterebra, are found in the Americas, where they are obligatory parasites of rodents and rabbits. The botfly proliferates by laying eggs on blades of grass or in nests, where they hatch, releasing maggots that crawl onto the skin of passing animals. The small maggots then enter a body orifice, migrate through various internal tissues, and ultimately make their way to the skin, where they establish themselves within the skin, creating a warble (a small lump in the skin). The mature maggots, which may be an inch long, then drop out of the rodent or rabbit host and pupate in the soil.
Cats become infected with a botfly larva when they come into contact with a blade of grass that has a maggot on it. The movement of the cat against the blade of grass stimulates the maggot to crawl onto the cat. The maggot then crawls around on the cat until it finds an orifice in which to enter.
In the northern U.S. the disease is seasonal, with most cases occurring in late summer and early fall when the adult flies are active. Seasonality is less determined in areas with warmer temperatures, where flies are active through longer periods of the year.
Symptoms and Types
Cuterebra infection may be detectable by warbles below the surface of the skin, or your cat may show signs associated with the larvae migrating within their tissues. Symptoms can include respiratory signs, neurological signs, opthalmic (eye) lesions, or the aforementioned maggots under the skin.
Respiratory symptoms:
- Cough
- Fever
- Shortness of breath
Neurological symptoms:
- Dizziness
- Circling
- Paralysis
- Blindness
- Lying down
Opthalmic symptoms:
- Lesions (caused by the larvae in the eyeball)
Skin symptoms:
- Lump in the skin containing the maggot, also called a warble; there will be a raised opening in the lump so that maggot may breathe
Causes
The most likely place for your pet to acquire this parasite is in an environment where the botfly flourishes: grassy areas where there are adequate populations of rodents and rabbits. But, even pets without access to the outdoors, such as newborn kittens, can be infected from larvae brought home on the mother's fur.
Diagnosis
Your veterinarian will want to consider the following conditions before positive diagnosis of a cuterebra infection is made. Respiratory symptoms will be evaluated for allergies, and for other possible parasites, like lungworms or other migrating worms that use the respiratory tract as a passage. Conditions that might produce similar neurological symptoms, but are of graver consequence, will need to be ruled out before treatment is given for a cuterebra infection. These conditions include rabies, distemper, and heart worms. If your cat has lesions on the eye, there may be a more serious parasitic larval infestation, one that can lead to permanent blindness, that also needs to be ruled out.
The clearest indication of a cuterebra infection is, of course, a warble under the skin, in which case your veterinarian will be able to quickly determine whether it is the botfly.
Treatment
If the maggot is at the end of its migratory stage and has settled into a spot on the body, such as under the skin, eyes, or nose, your veterinarian will be able to remove it safely. Manifestations of lung migration may be alleviated by corticosteroids. If the parasite has led to irreversible neurological damage the prognosis will be poor and euthanasia may be the only option.
Your veterinarian will probably prescribe a broad-spectrum anti-parasite medication, which should kill maggots still in the migrating stage. A corticosteroid treatment will be given before administering the medication. The anti-parasite medication can be administered either to alleviate the signs caused by maggots suspected of migrating in the lungs, or to kill larvae in other tissues, including the central nervous system.
Prevention
There does not seem to be any prolonged immunity to infestation; an animal can develop skin lesions due to botfly infestation for several years in a row. Application of monthly heartworm preventives, flea development control products, or topical flea and tick treatments may either prevent the maggots from developing in the dog or cat, or may kill the maggots before they have time to gain access to an orifice for entry.