Imagine you’re a vet doing an exploratory abdominal surgery in a dog. You’re poking around in the belly and feel something abnormal. You grab it and as you pull it out of the abdomen to have a look, you see it’s a red tubular structure. As you continue to pull (and pull, and pull), it just keeps coming… Eventually you realize it’s not attached to anything in the dog, and it comes out completely, partly to your relief but partly having to resist the urge to pitch it across the room and yell as you realize it’s a giant worm that’s squirming around as you handle it.

That’s a scenario we sometimes see with one of the grosser (and also largest) parasites of dogs (and other mammals), the giant kidney worm (Dioctophyme renale).

I’ve had a couple of calls this week about this parasite, both about worms found in dogs that were rescued from northern Manitoba, a relative hotbed region for D. renale.

Like a lot of parasites, this one has a somewhat screwy and complex life cycle. Adult worms live in the kidneys of various mammals, particularly mink. The worms lay eggs that are passed in urine. If the eggs end up in water, embryos form inside them If embryonated eggs are eaten by an intermediate host (an earthworm), larvae hatch and mature. If the infected earthworm is then be eaten by a mammal like a dog, or first eaten by a frog or fish (a paratenic host) that is then eaten by a dog, the parasite goes on a “road trip” around the body and usually ends up in the kidney (most commonly the right kidney), where it’s now completed its life cycle. However, since worms can grow up to 50 cm long and kidneys aren’t very big, the adult worms can destroy the kidney in the process.

Sometimes these worms are just an incidental finding that’s detected when imaging the kidney or abdomen for some other reason, or (as in this case) they’re seen directly during surgery, but otherwise don’t seem to be causing a problem. Sometimes the worms destroy one of the kidneys. Rarely, they cause damage in other areas of the body. The treatment of choice is physically removing the worm. That’s easy if it’s swimming around the abdomen. If it’s destroyed one kidney, the whole kidney gets taken out. If there are worms in both kidneys, then the animal is in trouble. Just like people, a dog can live happily with one healthy kidney, but zero kidneys isn’t an option.

For most people, there’s no risk of their dog being exposed to this parasite. The parasite is present internationally, but the risk tends to be focused in specific geographic areas. In Canada, most of the cases I deal with are from Manitoba and northwestern Ontario. People who live in areas where D. renale exists need to be aware of it and try to prevent their dog from eating frogs or fish, or earthworms. That’s easier said than done, though, because as many people know, if a dog has a tendency to eat things like that, it can be hard to stop it. It’s also important for people who move or adopt dogs from endemic regions – and their veterinarians – to be aware of the potential for dogs to be infected with this parasite.  (This is also a reminder that a rescue dog doesn’t need to come from outside of Canada to be at risk of some unusual diseases.)

Are people at risk for infection with D. renale?

• Yes, but not from infected dogs. People can get infected by eating the same kinds of animals that can result in infection in dogs (e.g. fish, frogs). Human infections are rare, but occur in areas where the parasite is endemic (especially when freshwater fish are a core component of the diet, and they may not always be thoroughly cooked).

Below is an old video of giant kidney worm removal (if you’re squeamish, don’t watch when eating lunch).  You can also click here for a slightly shorter, possibly more digestible and more recent video (also from the Ontario Veterinary College) of a similar case of D. renale removal in a dog.