Treatment Of Cuterebra Larva Infestation In Cats And Dogs

 Cuterebra.  Pronounce it CUTE-uh-REE-bruh.

They are anything but cute.

Cuterebra is a bee-like fly which lays her eggs in places where target mammals will come in contact with them. Such locations as the orifices of bird and squirrel nests, burrows and animal paths are favorites. Eggs may be laid on stones or vegetation. The fly’s goal is to get the eggs onto the coat of the host, from which the egg responds to the host’s body heat by hatching to a larval stage. The larvae then enter the mouth or nose during grooming. Less often an open wound on the body might be the entrance point.

Left: 3rd instar larva, Cuterebra spp. Right: 2nd instar larva, Cuterebra spp.
Left: 3rd instar larva, Cuterebra spp. Right: 2nd instar larva, Cuterebra spp.

The larvae then migrate to a subcutaneous (under the skin) spot on the body where they can make a tiny opening through the skin for breathing. The larvae spend about a month in the host, after which they emerge through the skin, fall to the ground and pupate (enter a cocoon stage).

Insect larvae undergo stages called “instars.” Early in the season, such as April and May we expect to see the second instar, which is 5-10 mm. in length and light in color. The third instar is much larger, as big as a child’s thumb, and much darker. They are usually adorned with spines.

So, under what conditions would a veterinarian interact with a Cuterebra larva? Dogs and cats are aberrant hosts, but do sometimes become infected. Wild rabbits and squirrels are the most common victims and can sometimes have a dozen or more Cuterebra cysts at once.

When a cat or kitten is presented to a veterinarian with a Cuterebra (colloquially called a “wolf” or “wolf worm”) the owner is typically baffled by the condition. The sight of “something” moving inside the wound is quite alarming. I say “cat or kitten” because, while dogs are reported to become infected with Cuterebra, I’ve not seen an affected dog in thirty years of practice.

Treatment starts with light sedation of the cooperative patient or general anesthesia of a cat who resists help. Hair is clipped from the area of the cyst and the entire clipped area is disinfected and prepared for surgery. Operating forceps are used to enlarge the opening sufficiently to allow extraction of the larva without undue compression. Rupture of the larva can lead to release of foreign material that may prevent the wound from healing. In some cases anaphylactic shock may take the patient’s life. The wound is thoroughly irrigated per standard abscess-treatment protocol.

Systemic antibiotics are indicated, and I have successfully used Convenia in Cuterebra victims. Ointments, such as Animax, are useful to irrigate the wound and help control infection topically while a systemic antibiotic works from the inside.

Prevention is mainly focused on keeping one’s cat indoors, instead of nosing around where cats don’t belong.

See you tomorrow, Dr. Randolph.

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Dr. Randolph
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104 Comments

  1. Jacqueline Lisseth Lara

    Hi. I just had my cat omitted to the vet to get stitched up because I found a huge hole on the back of his ear. By the looks of it, it look like it could have been a botfly larva. I don’t know where it went to expose of it and should I be worried about my two other dogs getting it? My cat was a stray I took in on Oct 2019.

    • Cats who become infested with fly larvae have usually stuck their heads in places they don’t belong, such as bird nests and squirrel nests. Indoor cats don’t suffer with these problems. Please keep your kitties indoors. Thanks for reading, Dr. Randolph.

  2. Hi,
    Two days before I saw three to four holes on the back of a street dog( puppy). I called a vet, he put some ointments on holes and gave an injection. He prescribed antibiotics, I am giving the dog the antibiotics, but he is not able to stand on his hind legs and is terribly weak. He is not able to walk properly. The vet said the worms will leave the dog’s body in few days. I am really worried about the pup he is just 5 to 6 weeks old.

  3. We rescued a bunny about 3 weeks ago, and we know nothing about bunnies We just saw her previous owners put her in the woods, at the time I just thought they were giving her time to run around since we live in apartments. Next morning I saw her outside and I was so angry and saddened that anyone would do such a heartless act. We caught her and brought her inside, and have been taking care of her since that day. We got her a cage, blankets, toys, green leafy vegetables, Oxbow pellets, and hay. We have been very loving to her. Yesterday I noticed something on her behind that looked like she had a poopy butt. So I watch a video on how to properly clean her butt. We got it nice and moist until I was able to remove it from her butt, however when it fell off it started moving!!! OMG it looked to be larvae of some sort, which we disposed of immediately, but we believe it was Cuterebra. Now that it has been removed and she is clean will she require antibiotics or will she be okay without having them? Any help would be appreciated. Thank you for your time!!!

    • Usually removal of the larva and keeping the site clean are sufficient. Be sure to check the area twice daily until it’s completely healed, and contact your veterinarian if there is any evidence of interference with healing. Thanks for reading, Dr. Randolph.

  4. I met a woman at my vet’s office several weeks ago who informed me that her previous dog has died from a Cuterebra infestation. She stated he was an “outside (farm) dog,” who had very limited interactions with people. I presume that is how the infection was able to reach a point that serious organ damage had occurred.

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