Cuterebra Infestation in Cats

If you have ever seen the Alien movies, you can relate to a Cuterebra infestation. Cuterebra are large flies who use dogs, cats, squirrels, rodents, and rabbits as hosts in which to grow more Cuterebras. A type of myiasis (maggot infestation), Cuterebra infestations can be rather disturbing to witness on your pet.

The life cycle of this fly is as follows:

  1. The mature fly lays eggs near the nest of rabbits or rodents.
  2. The body heat of the nesting animal causes the maggot to hatch into tiny worms.
  3. [This is where the science-fiction story begins….] The tiny maggots travel through the nose, mouth, or a skin wound and migrate under the skin of a poor nesting creature.
  4. In some cases, dogs and cats pick up a wandering maggot when investigating the nest of a rabbit or rodent.
  5. Once under the skin, a cyst forms around the maggot and the little parasite grows to as much as 1 inch in length, living happily under the host’s skin.
  6. Worse yet, a small breathing hole appears in the host’s skin, and you can actually see the Cuterebra poking his alien head out of the cyst!
  7. Eventually, if no human intervention takes place, the Cuterebra grows up and leaves the cyst to start the vicious parasitic cycle all over again!

In cats, the Cuterebra maggot is most often found near the head or neck.

Your cat will be luckier than the characters in Alien because, with appropriate treatment, she won’t die as a result of this infestation. If your cat is hosting one of these nasty bugs, you or your veterinarian can diagnose the issue by visual inspection. For removal, however, it is highly recommended you visit your veterinarian because the maggot must be removed whole, not severed in the extraction process—doing so could cause an allergic reaction in your feline friend.

Once the maggot is removed, your veterinarian will most likely flush out the opening and may prescribe antibiotics to reduce the risk of an infection.

The best way to prevent an “alien” from invading your four-legged friend’s skin is to limit her exposure to rabbit and rodent nests. Frequently check your cat’s skin for bumps and other abnormalities, and be sure to contact your veterinarian if you suspect anything out of the ordinary.

If you have any questions or concerns, you should always visit or call your veterinarian – they are your best resource to ensure the health and well-being of your pets.

Hespeler Animal Hospital

We often see sneezing, congested and sick cats this time of year (summer). If they have access to the outdoors and their vaccinations are current, one of the most likely causes is Cuterebra.
What is that?

A Cuterebra is a maggot-like parasite with short bristly spines. A Cuterebra fly is a large, fat bot fly found throughout North America. There are 34 species of Cuterebra in North America. The fly itself does not bite, however, its larvae need live hosts to develop. The female fly lays her eggs near rodent (e.g. chipmunk) and rabbit burrows. The eggs attach to an animal’s coat upon contact with the burrow. The eggs then hatch and travel to any opening on the body. This can include the mouth, nose or an open wound on an animal. Once inside, the larvae travel through the body to specific locations on the head, neck or body. While rodents are the preferred host of the Cuterebra larvae, cats can be accidentally infested.

What can you do to prevent Cuterebra in your pet. The best thing is to keep it indoors (the birds will thank you) or only allow outdoor access from a pen. Plan B is to treat with a flea and tick preventative such as Revolution. Although this is off-label use and efficacy against Cuterebra in untested, it makes sense that a medication that kills fleas and ticks will likely also kill other external parasites. And, if your cat goes outside, it should be on a preventative anyway!

For more information, check out this great article:

Overview of Species

Canine and Feline

  • There are some 34 accepted species of Cuterebra in North America.
    • Species have also been reported from Columbia, Brazil, Argentina, and other South American countries.
  • These flies undergo a period of obligatory parasitic larval development in rodents and lagomorphs.
  • The subgenus Cuterebra (comprising 12 species) parasitizes rodents, and the subgenus Trypoderma (comprising 22 species) are parasites of rabbits.
  • Cats and dogs are accidental hosts.
  • Genus and specific identification by simple morphological examination of larvae (bots) may be difficult to impossible, especially in younger forms.

The Cuterebra in Dogs and Cats

Cuterebra is the scientific family name of the North American rabbit or rodent botfly.

Most of the general public are not aware of what a cuterebra is or have had a pet that has been lucky enough to avoid being infected by one. As an RVT of 18 years, I myself have only been a whiteness to a handful of cases until I was affected close to home. I recently rescued a kitten living outside on its own that at first glance had an infected wound on its chest. With no other wounds on his body, only a discharge from the eyes, I found it peculiar until I discussed the case with one of my veterinarians. One of his rule outs was a cuterebra infection, which became a scary reality when a cuterebra larva was removed from the open wound on my kitten’s chest.

After this experience, I decided to do further research. Dogs and cats act as accidental hosts for cuterebra larval development within their tissues.

You may be thinking, how can my pet become infected? Dogs and cats become accidentally infected when investigating rabbit or rodent burrows, where adult botflies deposit their eggs. After hatching, the larvae will enter the body through an opening, like the nose or mouth, or through a skin wound. The larvae, after several days, will migrate to the tissues where they encyst, and development is continued. As the larvae grows it becomes a noticeable swelling beneath the skin. A small breathing hole, or cyst, will be visible on the face, neck or trunk over the larvae and will enlarge when the larvae is mature and ready to leave between 3-8 weeks after entering the tissues. The cyst may cause a serious or purulent discharge that is 3-5mm in diameter.

The larvae may migrate to the brain tissue, in cats, and symptoms could include lethargy, seizures, blindness, abnormal vocalization or gait, and abnormal or no reflex responses. Violent sneezing attacks may also occur weeks before other clinical signs. The larvae may also migrate to the respiratory system tissues causing difficult breathing in cats. Occasionally no symptoms are evident until the larvae have migrated from the body and the empty cyst becomes infected or develops into an abscess.

Treatment varies with when the infection is identified. The less mature larvae can be removed by surgically opening the cysts that have formed in the skin. Mature larvae are dark, thick, and heavily spined. These can be removed with forceps from the cyst opening. The tissues are then flushed, debrided, and left to heal by granulation. In some cases, surgical closure of the tissue may be needed. If the larvae have already migrated out, the above procedure is followed, and antibiotics prescribed. Larvae that have migrated to body tissues must be surgically removed. With any of these treatments, it is highly recommended to visit your veterinarian for proper and safe removal of the larvae.

For those of you wondering if my kitten survived this infection, the answer is yes! The prognosis, of course, is worse if your pet is infected with multiple larvae or if they have migrated to a nerve, other sensitive tissues or organs. I hope sharing my experience has not frightened you but left you more empowered against these parasitic flies.

A 3-year-old female, spayed Persian cat, presented, after sneezing and nasal discharge 1 to 2 wk earlier, with acute onset focal and generalized seizures, progressing to obtundation. Magnetic resonance imaging (MRI) of the brain showed subtentorial and transforaminal brain herniation, with visible meandering tracks of parenchymal hyperintensity on T2-weighted images, and on post-contrast T1-weighted images, corresponding to eosinophilic track lesions on histopathology ( Figure 2 ). This correlation between MRI and histopathology findings has not been reported in a cat.

A — A T2 Fast Spin Echo-weighted magnetic resonance (MR) image in the dorsal plane of a 3-year-old female spayed Persian cat with acute onset seizures and depression after sneezing and nasal discharge in the preceding 1 to 2 wk. Hyperintensity of the parenchyma may be seen at the base of the left hemisphere, tracking caudally to the left rostral medulla and cerebellar peduncles. B — There was a corresponding enhancement on post-contrast T1 weighted-MR image. C — Histopathology of an involved portion of cerebellum from the same cat pictured in A. Hemorrhage and necrosis were found, surrounded by an eosinophilic inflammation. D — Detail of C showing eosinophilic inflammation surrounding the area of hemorrhage and necrosis.

As was seen in Case 2, the diagnosis is obvious if a Cuterebra larva is found (2,6,10). Inspection of the upper respiratory tract may identify a larva (2). Clinical suspicion of cerebrospinal cuterebriasis is raised when confronted with a history of upper respiratory signs 1 to 2 wk prior to onset of intracranial neurologic signs, as in Cases 1 and 3 (2,7,8,19). Abnormal body temperature has been reported (7). The hemogram may show a peripheral leukocytosis with eosinophilia (2,7). Globulin concentration may be increased on the serum biochemical profile (7). Cerebrospinal fluid (CSF) analysis may show a pleocytosis with eosinophils, neutrophils, or mononuclear cells, and an elevation in total protein (2). Computed tomography (CT) shows a mottled appearance to the brain, consistent with encephalitis (7,21). Magnetic resonance imaging may show linear regions of hypointensity on T1-weighted images, hyperintensity on T2-weighted images, and contrast enhancement, with the possibility of small areas of hemorrhage (21,22). Characteristic histopathologic features include parasite tracts, superficial laminar cerebrocortical necrosis, cerebral infarction, subependymal rarefaction and astrogliosis with or without ependymal cell loss, and subpial astrogliosis (7,9,20). Certain of these features, occurring within the brain parenchyma independent of the location of the larva or its track lesions, are similar to lesions reported for feline ischemic encephalopathy (FIE) (9,20).

This latter observation contributes to the argument that cerebrospinal cuterebriasis causes FIE. Additionally, where Cuterebra species are not geographically present, FIE is not reported (7,9). Furthermore, the seasons for occurrence and the clinical signs of the 2 diseases overlap (9). It is postulated that the migrating larva elaborates a biochemical mediator resulting in vascular spasm, for example, oxyhemoglobin and its derivatives from focal hemorrhage or a parasite-produced toxin, that circulates in the CSF bathing the cerebral arteries, thus inducing ischemic infarct (9). It has also been suggested, though not proven, that cuterebriasis may be a causative agent of feline idiopathic vestibular disease (7). This hypothesis is based upon similarities between seasonal occurrence and history of outdoor exposure in cats with idiopathic vestibular disease and cats with cuterebriasis. Confirmation of this hypothesis has been stymied by the high rate of recovery of cats with idiopathic vestibular disease, reducing the opportunities for postmortem examination (7).

Prognosis depends on lesion localization, clinical signs, and response to therapy. Animals may die within hours of onset of signs, sustain permanent neurological deficits, or recover to an acceptable level of function and quality of life (8). It is thought that cats with cuterebriasis resembling feline idiopathic vestibular disease will likely return to completely normal function (7).

There are no reported clinical trials for treatment of cerebrospinal cuterebriasis, possibly because of the difficulty in achieving antemortem diagnosis. Surgical removal of the offending larva has been suggested, but not reported (2). Ivermectin has been the therapy of choice in the majority of case reports (2,7,8,10,12). One report described the use of levamisole at 60 mg/d for 7 d (8). Ivermectin, at 0.1 mg/kg, is effective against Cuterebra species (2). Reported doses ranged from 0.2 mg/kg subcutaneously (10), 0.3 mg/kg subcutaneously every 48 h for 3 treatments (8), or 0.3 mg/kg orally every 14 d for 2 treatments (12) to 0.4 mg/kg subcutaneously every 24 h for 3 treatments (7). For presumptive cerebrospinal cuterebriasis, ivermectin may be given orally (2). Corticosteroids are recommended alongside ivermectin to prevent additional inflammatory damage during the treatment period (2,7,8). Doses range from prednisone [1 mg/kg, PO, q12h, for 3 wk, then q24h for 3 wk (2)] for cats with upper respiratory syndrome and a presumptive diagnosis to dexamethasone [0.1 mg/kg, IV, given at the same time as the ivermectin q24h for 3 treatments (7)]. Larval disruption has been associated with a Type I hypersensitivity-like reaction (2,7,8). Diphenhydramine pre-medication (4 mg/kg IM, 1 to 2 h prior to ivermectin administration) has been recommended to mitigate this possibility (7). Antibiotics (for example, enrofloxacin, 5 mg/kg, PO, q12h for 14 d) have also been administered in case of bacterial introduction during larval migration (7). A preventive program may be recommended (2), including owner education, lifestyle changes for cats with outdoor access, careful monitoring of “respiratory infections” in the late summer and early fall, and monthly administration of anthelmintics (such as, fipronil, imidacloprid, moxidectin, milbemycin oxime, selamectin, or ivermectin) (2,10).

In conclusion, cerebrospinal cuterebriasis represents a common neurological disease in cats presented during the summer months with acute to peracute onset of multiple cranial nerve deficits and other neurological signs often preceded by upper respiratory airway dysfunction. Early diagnosis and treatment may lead to complete recovery of function or at least an acceptable long-term quality of life.

Watch the video: Cat Rescue Botfly Larva Removed From Cats

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