Wednesday, May 29, 2013

Wormy Wednesday!

Wormy Wednesday!

It’s been a grotesquely long time since I’ve done a Wormy Wednesday, but I have good reason for one today, so here we go!  

A few weeks ago I had the great privilege to visit the United States’ National Parasite Collection (USNPC).  Bet you didn’t even know there was such a thing, did you?  Tucked quietly away at a USDA office in Beltsville, Maryland, an extremely unassuming building, nay, the BASEMENT of the building, holds the most amazing collection of parasites, both endo and ecto, in the world.  This is not just uber-veterinary-nerd-hyperbole.  It really does house the largest specimen collection in the world.  Of course it helps when most of your specimens are teeny tiny like fleas and sections of cattle liver fluke on a microscope slide.

Walking into this basement is a surreal experience.  At first, you just see compressed shelves – you know, the type that are on rollers to save space.  But when the shelves are opened up and you peer down one, you see jars upon jars of things in formalin.  And I love jars of things in formalin.  There’s just something fascinating and creepy all at the same time about something that’s been preserved for the past fifty years in a Mason jar filled with yellowing liquid.  Maybe this is the mad scientist in me speaking out.  I don’t know.  Perhaps I’m abnormally riveted by this sort of stuff.  

Yay! Random jars!
My abnormalities aside, the breadth of the collection combined with its history is practically awe-inspiring.  There were specimens in there from the last half of the 19th century!  The host animals ranged from the dog to Antarctic seals. 

However, in my opinion, for any parasite collection to be worth its salt, it must contain one of my most favorite parasites: the canine giant kidney worm.  My fascination with this parasite dates back to my vet school days in parasitology class, sophomore year.  Our professor had a modest collection of parasites for lab use, as most parasitologists do.  During labs we would examine ad nauseum the feeding and breeding apparati of various nematodes, trematodes, and cestodes (ooohh, look at that spicule!  Wow is that an excretory pore or what?) of prepared slides which were more than showing their age under the microscope.  Most interesting to me were the jarred specimens sitting at the front bench.

There was one specimen that immediately caught my eye – a kidney cut longitudinally.  Within this kidney was a worm.  Just a worm.  This thing had obliterated the entire inner structure of this organ and set up shop inside.  It was horrifying.  And so extremely fascinating.  Here are the deets:

The giant kidney worm is more politely called Dioctophyme renale, or D. renale for short.  It’s true host is the mink but occasionally an unlucky dog can become an unsuspecting host.  Eggs of D. renale are passed in the urine of the infected animal.  These eggs then go through a complicated life cycle involving various intermediate hosts such as fish and frogs.  With each pass through an intermediate host, the parasite slowly matures.  Then a mink (or dog) comes along and eats a fish or frog that is harboring these developing larvae.  Once ingested, the larvae of D. renale migrate eventually to the kidney where they grow to adults, breed, and pass eggs into the urine to start the life cycle over.

Here is D. renale in all its kidney-destroying glory.
One of the most interesting details of this parasite is that it only ever infects one kidney, and specifically, almost always the right kidney.  Although I’m not sure why the predilection for the right kidney, the parasite seems to know that if both kidneys were infected, the host animal would die.  And when you’re a parasite, you don’t really want your host to die, otherwise you're out on the street looking for a new place to rent.  So this adaptation of the one-kidney-only rule allows for the successful survival of this parasite.

Unlike common gastrointestinal parasites like tapeworms and roundworms which reside in the intestines and can cause weight loss and diarrhea and are diagnosed via fecal sample, D. renale is usually diagnosed when the host animal succumbs to kidney failure (since one kidney has been obliterated).  Treatment is removal of the infected kidney.

Although this all sounds really scary, fear not.  Even though the parasite has been reported across the United States, it is really, really rare to find it in dogs.  Are you a mink owner?  Well, then maybe be a little more worried about it.  I don’t know – I don’t treat minks.  Prevention is to not let your dog eat raw fish, frogs, and other icky wigglies out in the wild…. But try telling that to a Labrador.  Good luck.

A mink. Because I wasn't quite sure what one looked like. Appears similar to a ferret. Man, those are some beady little eyes!

So, anyway, to get back to my epic adventure in the halls of the USNPC, with bated breath I asked the question: “Do you or do you not have the giant kidney worm?”

And I was not disappointed.

There, on a table, was a dog kidney encased for eternity in a clear block of plaster.  Inside this kidney was D. renale, all curled up and tucked in, cozy as could be.  Amazing.  My trip was complete. Sadly, there were no postcards to purchase.


1 comment:

  1. Sounds like a field trip might be necessary next time I'm in the DC area!

    I'm quite curious about how new kidney worms know that they're not allowed to parasitize a dog's second kidney when there is already one of their kin in his first. Does the incumbent worm send out some type of chemical signal warning others off? Or are they just generally benevolent creatures who would rather die themselves than take their chance at making a home in that second kidney? Sounds like a PhD project in the works...