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Hiding in the Grass

Cuterebriasis is a potentially serious condition that can affect any cat or dog that spends time outdoors. Cuterebra are species of flies that live for short periods of time during the summer and early fall in Minnesota. While the adult fly is non-biting and poses no risk to your pet, the larvae can cause significant problems including skin lesions, respiratory problems and even neurologic signs. To explain this, we must first look at the typical life cycle of the fly.

Cuterebra flies lay their eggs on grass near the dens of their natural hosts, rabbits (or in some cases rodents). The eggs hatch and the tiny larvae attach to the hair of their hosts and are ingested when the rabbits groom themselves or are inhaled as the rabbits sniff the grass. The larvae then migrate through the body tissues until they are just under the skin surface, usually around the rabbit’s back. Here the larvae continue to grow, form a swelling or warble with an opening in the skin and eventual emerge out of this opening and fall onto the ground. It takes approximately 3 to 4 weeks for the larvae to mature in the host. Once out of their host, they burrow into the ground where they pupate, to emerge the next year as an adult Cuterebra fly. 

Cats and dogs can become infected in the same fashion as rabbits from eggs or larvae on grass in areas near where rabbits live. The initial signs of an infection may be sneezing or coughing episodes as the larvae migrate through the upper respiratory tract including the nasal cavity, the pharynx, trachea or esophagus.  Several weeks later, the larvae may eventual cause a skin swelling with an opening that your cat or dog may lick and can be mistaken for a wound. These often are around the head and neck of cats.

More serious signs can occur if the larvae becomes lost on its journey to the skin surface, which appears to happen more frequently in cats rather than dogs. The larvae can cause serious respiratory difficulties if they continue to remain in the upper respiratory tract and grow there rather than in a skin swelling. Some larvae will even migrate through the nervous system and infect the brain! This can lead to behavior changes, neurologic dysfunction or even seizures.

If you suspect your cat or dog could have a Cuterebra infection, talk with your veterinarian. DO NOT squeeze any area of swelling that could contain a Cuterebra larvae as breaking the larvae open in the skin could cause a serious allergic reaction or anaphylaxis. The best preventative measure is to keep your cat indoors and to keep your dog away from areas where rabbits live.

For more information, please visit the companion animal parasite council website: http://www.capcvet.org/capc-recommendations/cuterebriasis/ 

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