The worm that your mommies always warned you about
Once upon a time, a little boy took his beloved little puppy on a warm summers day out in the woods, where the two of them played around in the warm soil beneath the trees. The puppy was so delighted to be running around and smell all these exciting things that it rolled around in the warm soil and never felt so happy. When the two of them came home there was a lot to tell mommy, and the puppy sat on the little boys lap and licked his masters face excitedly.
A couple of weeks later the little boy started to complain about pains in the right upper part of his tummy and the nice doctor around the corner diagnosed a tummybug and gave the little boy some paracetamol. A couple of years later the pains appeared again and the boy had to be admitted to hospital. There the surgeons diagnosed on his CT a large cyst full of worms in his liver and operated on him the same day. Just when the surgeon wanted to make an incision around the cyst to dig it out, a nurse sneezed and hit the surgeons elbow and his scalpel punctured the cyst and ripped it open, and all its contents emptied into the little boys abdominal cavity, and a couple of minutes later the boy was dead due to anaphylactic shock. The End.
Echinococcus granulosus is a tapeworm whose larvae cause hydatid disease in humans who pick up the eggs from their dogs, who might have them from infected soil or after eating infected rodents. When ingested, the larvae accumulate in the liver, brain or lungs and start developing large, multiloculated cysts surrounded by a fibrous wall.
The cysts consist of of a sphere of epithelium containing brood capsules and fluid. The cysts may develop large daughter cysts, each containing more brood capsules, getting bigger for years.
In some areas, these cysts are the most common reasons for masses found in human abdomens. Their behaviour is unpredictable, as they are able to spontanously burst and cause a quick death due to anaphylaxis.
Although all the factors causing human infection are already known, there are still endemic areas in the UK and the US. Regular worming of dogs seem to be an effective measure to help eradicating the disease in your dog.
Treatment is mainly surgical by removal of the cysts but highly dangerous. Albendazole has shown some promise as well, but it is still preferable not to be infected at all, so the next time your dogs wants to lick your face or you play with your dog and then want to pick your nose:
Think twice and wash your hands.
Dion R. Bell: Tropical Medicine, 4th edition, Blackwell sciences, 2000