Monday, October 20, 2014

Cuterebra infection: Not really that cute...

Gryffin
Meet Gryffin, a tiny little kitten found wedged between the wall of a gas station and the ice machine. He weighed less than two pounds, and had a wound on his leg. Upon examination by the doctor, it appeared to be a run-of-the mill bite-wound abscess. Once under anesthesia, we were able to take a closer look - clipping up the hair and scrubbing the wound with antiseptic scrub. Bite wound abscesses have a tendency to become infected, so Dr. Brooks removed the scab and flushed the wound. As would be expected, the wound was infected. After cleaning it out, the doctor gently probed the wound and determined that it was clean. We treated Gryffin with pain medication and antibiotics.

But, Gryffin didn't get better. His wound still seemed to bother him, and we examined him again. The wound was free from infection - what could it be? Dr. Brooks commented that it was a remote possibility that it was a Cuterebra breathing pore, but no Cuterebra was found in the wound, and the pores do not scab over while the larvae are inside. It was also an unusual site for a Cuterebra infection, since Cuterebra larvae generally infect the head and neck regions of cats. She decided to satisfy her curiosity non-invasively, by placing the ultrasound probe on Gryffin's leg. This is what she saw:

Ultrasound image of a cuterebra larva
Deep within the wound, far from the scabbed opening, a dead Cuterebra lay - acting essentially like a sliver under the skin, causing irritation and infection and pain. Dr. Brooks was now able to locate the larva and remove it, much to Gryffin's relief! We measured the Cuterebra once it was removed, and determined that it was the biggest one we had ever seen, at 4cm in length.



Cuterebra larva after removal

Cuterebra. It doesn't sound too bad, and usually, they don't cause too much trouble, but Cuterebra larval infection can cause problems for cats.

The Cuterebra larvae are immature bot flies - a large bumblebee sized fly. The adult flies are harmless - in fact, they live for such a short time, they do not even have mouth parts for eating!
Adult Cuterebra
They lay thousands of eggs in the environment (blades of grass, wood chips - areas near rodent burrows) or on other insects (such as mosquitoes), or even directly on the host (such as horses) - usually in clusters of 5-15 eggs. Cats and dogs are not the normal host of the Cuterebra, but can become infected if they spend time in areas where the eggs have been deposited. The eggs tend to hatch quickly when exposed to the warmth of a nearby body. Most of the time, cats will become infected by coming into contact with a newly-hatched Cuterebra larva with the nose or mouth, but the Cuterebra can also enter the body through open wounds.

Once in the body, the larva forms a small cyst under the skin - most commonly near the face and neck. These lumps are usually very easy to distinguish from a cancerous lump by the 2-4mm breathing pore that the larva creates. Often, the larva can be seen moving towards and away from the pore to breathe. These lumps are called "warbles". It is most common to see the warbles in late
August and September. Some years, we see a lot, other years, we see none. In the Waterford area, kittens tend to be most commonly affected, but any cat that goes outside could come into contact with a Cuterebra larva.

Sometimes, a sneezing cat may have a Cuterebra infection in its nose. On some rare occasions, a Cuterebra infection may occur in or near the eye or spinal cord. These situations are very rare. Cats that develop eye infections may or may not have damage to the eye. Neurologic signs of Cuterebra infection may include "head pressing", circling in one direction, or other behavioral changes. Cats that develop spinal cord infections may fully recover once the Cuterebra larva is removed.

The most effective treatment for Cuterebra infection (called "cuterebriasis") is surgical removal of the larva. In some situations, this can be quite complicated, depending on the location of the larva. It is important to be able to remove the entire larva, and not to break the larva while it is inside the cat, or a severe allergic-type reaction can occur (called "anaphylaxis"). 



It is important to remember that you can NOT get a Cuterebra infection from an infected cat, but you may have Cuterebra present in your yard.

Two weeks after removing Gryffin's parasite, he looks great!
In Michigan, late summer and early fall is the time of year that Cuterebra infections become evident. The larvae are very difficult to see until they become large, due to the fur coat your cat wears. Some years, we do not see any cats with Cuterebra infections, other years we see quite a few. This year, we saw a cluster of 4 cats with Cuterebra infection, all in a row at the end of August and early September. Two of the cats had Cuterebra larvae in the neck region, Gryffin had his infection in a hind leg, and one Cuterebra was located up a cat's nose! He had a "chronic upper respiratory infection" that would get only a little better with antibiotics. Some might have written that off as a viral infection (viruses do not respond to antibiotic treatment), but Dr. Brooks took a look up the cat's nose and there was the source of the chronic sneezing! Once the Cuterebra was removed from the cat's nose, he fully recovered.

These days, Gryffin is doing much better, without his creepy-crawly passenger!

EDIT: 11/4/14 Gryffin came in for a recheck and had gained almost a pound since his last visit. His wound is healed and he is looking and feeling great!


For more information:
Article on Cuterebra from the American Association of Veterinary Parasitologists