Botflies in Cats

Cats are usually an accidental host that picks up the botfly larvae when exploring near rabbit or rodent dens. Cats that spend a great deal of time outdoors are at a greater risk, and infestation occurs most frequently in the summer. The larvae can be found most commonly under the skin, but can also make their way to the eyes, respiratory system, or central nervous system where symptoms can become severe and result in death if not treated quickly.

Botflies are a species of non-biting flies found throughout most of North America. The species is especially active in the warmer months of late spring and summer, but can be found for a longer period in warmer climates. The botfly, or Cuterebra, life cycle involves a parasitic larval stage that requires a host animal, usually a rabbit or rodent. The adult fly lays its eggs on surfaces, like grasses and rocks, in and around the living areas of rabbits and rodents. The eggs or young larvae transition to the host animal by transferring onto its fur when it walks past. They then make their way into the host through an opening or orifice. 

Symptoms of the botfly larvae parasite can vary depending on the location of the larvae within the cat’s body. Cutaneous or skin symptoms are the most common form, although the parasite can affect the central nervous system, respiratory system, and the eyes. Nervous system symptoms often begin with nasal discharge or sneezing as the larvae enter through these orifices. In certain situations, especially when the central nervous system is affected, the symptoms can be severe and even fatal. 

General Symptoms:

• Fever
• Lethargy
• Lack of appetite 

Cutaneous or Skin Symptoms:

• Lesion or draining sore
• Lump under the skin or “warble”
• Excessive grooming of specific site

Respiratory Symptoms:

• Cough
• Sneezing
• Gagging
• Nasal discharge
• Trouble breathing

Ophthalmomyiasis or Eye Symptoms:

• Lesions
• Facial paralysis
• Blindness

Nervous System Symptoms:

• Abnormal behavior
• Head pressing
• Disorientation 
• Head tilt
• Abnormal vocalization
• Circling
• Abnormal gait
• Lack of reflexes
• Seizures
• Paralysis

Exposure to botfly eggs or larvae usually occurs outdoors in areas where rodents or rabbits make their homes. Physical contact is required for the parasite to infest its host. Cats come into contact with the eggs or larvae in these areas, and it is transferred to their fur from grass, leaves, or other surfaces. It is possible for a cat to bring the larvae into the home, infesting other cats or companion animals. Symptoms are caused by the movement of the larvae within your pet’s bodily systems and the effect it has on surrounding tissues as it begins to grow.

A physical examination is often sufficient for identifying cuterebrosis, in which case the parasite has reached the stage where it has settled under the skin. The veterinarian will locate the cyst or warble on your cat’s skin and evaluate it for larval infection. Be prepared to discuss your pet’s medical history and advise your veterinarian if the cat spends time outdoors. If the parasite is in the eye, it is also fairly simple to diagnose through observation. Testing may be necessary to confirm that the disease is caused by the botfly and not another parasitic or bacterial infection. To test for Cuterebra larva, analysis of blood, urine, and discharged fluid is required. Identifying parasite-produced toxins in bodily fluids will help to confirm the diagnosis. Testing of cerebrospinal fluid may also be necessary, especially if neurological symptoms are present. Imaging technologies, like an MRI or CT scan, may also help veterinary staff to identify Cuterebra in the central nervous system. 

Treatments will vary depending on your pet’s symptoms, their severity, and the location of the parasite. Medical treatment is required, and is usually effective, especially if cuterebrosis is caught early. Do not attempt to treat your cat at home, even if the larvae or warble is visible. There is a high risk of rupturing the cyst or larvae and causing an infection or introducing toxins into your pet’s bloodstream. When found near the skin, the prognosis after treatment is good. Larvae in the eyes or nervous system are more difficult to treat. Treatment options your veterinarian might use include:

• Extraction: If the larvae have made their home under the skin, the veterinarian will extract it. This is not a surgical procedure, so your pet will not need to be put under. A local anesthetic is used to numb the area, and then an incision is made so the larvae can be removed. Your veterinarian will take care to remove the entire parasite intact to prevent complications associated with rupturing or leaving behind a portion of the larvae. 
• Surgery: If the larvae are not as easy to reach, a surgical procedure may be required to remove it. Surgery puts your pet at a higher risk of side effects than extraction does. Your pet will undergo anesthesia, will require intravenous fluids, and may need a longer recovery time. 
• Antiparasitic: This type of medication is used to kill parasites throughout your pet’s body. It may be used in conjunction with extraction or surgical methods, but can also be used alone. It is often used to treat botfly parasites that are in the respiratory, nervous, and other systems where removal is not an option. 
• Corticosteroids: This type of medication is used to suppress immune reactions and aid in keeping inflammation under control. Corticosteroids treat symptoms in the respiratory and nervous system, are not effective for removing or destroying the parasite.
• Antibiotics: This type of medication will be administered if an infection is present either at the larval site or in other parts of the body the parasite moved through. Antibiotics are only necessary if bacteria are present. 

If the cuterebra larvae are successfully removed, the prognosis is generally good. The lesion or wound site where the larva was removed may take some time to heal. Monitor the area for signs of infection and make another appointment to have the wound checked if it seems to be swelling, draining pus, or spreading. Cats that experience eye infestations could lose sight in the affected eye. Your pet will still be able to lead a full life even after partially losing their vision. For cats suffering from nervous system symptoms, recovery may be less certain. Damage to the brain or other parts of the nervous system could be permanent or even fatal. Treatment should help, but your pet may not make a full recovery. Take care to support your pet during recovery and avoid stressors or making changes to their living environment.