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.
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.