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.