Paws for Thought

Veterinary Creepshow

by Dr. Janice Mitchell

Caveat lector – reader beware! The following article is dedicated to one of our employees who finally heard the chorus ‘creepy crawly’ in a Who song, ‘Boris the Spider.’

Yes, for those who like gross things, this is all about some of the past year’s unusual and exotic worms that we have discovered in some of our pets. Remember, these are rare occurrences and I do not mean to create panic…just a fun, Manitoulin Veterinary “Ripley’s Believe It or Not.”

Early this year, on a routine urine examination, an unusual egg was discovered under the microscope. Eggs in urine sediment are definitely not a common finding and thus the scientific antennas pick up. The shape and size of this egg, confirmed by textbook photos, revealed a parasite called Dioctophyma Renale aka the giant kidney worm. In veterinary school, it was mentioned briefly in the multitude of parasites veterinarians had to learn, and freaky stories of finding a large alien-like worm in the abdomen of a dog while performing an ovariohysterectomy were mentioned. Ewwwww. Would we vet students ever see one? Well, after this year, the life cycle of this worm needed to be reviewed as we did discover one case.

As the name indicates, the giant kidney worm is one of the largest roundworms.  Females can reach one meter in length. This parasite is found more frequently in the centre of the right kidney or free in the abdomen. The parasite is a bad tenant and destroys the kidney. The adults produce eggs that develop in water. Eggs do not hatch until ingested by earthworms or may parasitize crayfish. The crayfish in turn are ingested by catfish. Dogs become infected by ingesting crayfish, earthworms or catfish.

In our situation, this dog had been a Northern Manitoba rescue, and had to have been eating a raw fish based diet. Once diagnosed, there are no anti-parasitic medications that are effective and the damaged kidney and resident worms should be removed. However, it is very unlikely for these worms to inhabit and damage the remaining kidney. Many dogs can live a normal life with this disgusting inhabitant.

So, if you haven’t been turned off yet we will venture into our next ‘creepy’ case. A little dog was presented with a lump on the top of his head. It had developed pretty quickly and thus the reason for concern. Upon examination, the centre of the lump seemed to be open, and a creamy white colour was noted within. This little dog actually had a little grub-like worm inhabiting the ‘lump.’ A diagnosis of cuterebra was made…or rabbit bot fly. Adult cuterebra flies lay eggs at the entrance of rodent and rabbit burrows during the summer months. Eggs are stimulated to hatch from the warmth of the animal’s body as it enters the burrow. Larvae attach themselves to the animal’s coat and enter through any opening. The larvae migrate through the host and usually stop in subcutaneous tissues. After approximately three to four weeks, the larva forms a visible nodule (a warble) with an external breathing hole. After completing development, the larva, approximately 1-2 cm, exits the host and pupates on the ground. Cats and dogs may become infected by sniffing or sticking their head in a rabbit or rodent burrow. Any age, breed, or sex of dog can be infected; however, in one study of 20 dogs with cuterebriasis, 80 percent weighed less than or equal to 4.5kg. Yorkshire terriers accounted for 40 percent of the study population, which is not surprising since terriers were bred to slip down rodent holes. Affected patients may have no clinical abnormalities other than a focal swelling containing the larva (a warble). No treatment is necessary other than removing the offending ‘grub’.

Now to an even more exotic worm that apparently evaded the veterinary parasitology lectures at school, one that this author has endearingly called “the Dracula worm!”

Dracunculus insignis infection was diagnosed in a dog that presented with a swelling on his lower front limb. A long thread-like worm was discovered to be living within and removed.

Infection with D. insignis occurs by ingesting infected tadpoles or frogs. Larvae penetrate the small intestines of the dog and migrate to the subcutaneous tissues of the thorax, abdomen and inguinal area. After mating, the male worms die while the females migrate to the subcutaneous tissues of the limbs and abdomen. The presence of the adult worm in subcutaneous tissues leads to formation of a nodule that eventually fistulates. When the dog enters cool water, the female worm releases larvae that exit through the fistula. Overall prognosis for D. insignis infection is good, with complete removal of the worm. Antiparasitic medication is ineffective.

Now that you are thoroughly grossed out, the take home message of this creepshow is: Don’t eat raw fish, don’t eat raw frogs;,and don’t go sniffing around rabbit holes. And finally, don’t go down to the garden and eat worms, especially the big, fat juicy ones.