Medical Fun Facts Podcast

MFF0019: Echinococcus

I was really tempted to do Escherichia coli or E. coli. That would be too obvious though. I’ll do E. coli another time. Instead, I’ve chosen Echinococcus.

So what is Echinococcus? The genus, in general, is composed of tapeworms but a bit different to the pork and beef tapeworms you may be familiar with. The echinococci are much shorter than those tapeworms. Specifically, I’m interested in Echinococcus granulosus. Echinococcal infection causes hydatid disease or echinococcosis.

The echinococci don’t have an anus and they do not have a digestive tract.

In humans, three species form three different forms of the disease, viz., cystic, alveolar and polycystic.

The incubation period can be years, even decades. It is a zoönosis with definitive hosts being dogs in Australia. The adult tapeworm lives in the dog’s small bowel and produces eggs which appear in the dog’s faeces. Intermediate hosts get infected by ingesting the eggs. In Australia, the most common intermediate hosts are sheep, with humans being occasional intermediate hosts. When dogs eat the infected flesh of dead sheep, the infection cycle continues. Humans are regarded as dead-end hosts because dogs tend not to eat dead humans, although I do have a great story from my time in Darwin about dogs eating someone while he was unconscious.

The eggs hatch in the intestine of the intermediate host, e.g., a human, and the larva penetrates the bowel wall and is carried in the blood to the liver, lung, brain or another organ. Once in an end organ, the larva matures and forms a cyst, a hydatid cyst.

If a cyst is disturbed, e.g., by a surgeon who isn’t familiar with hydatid cyst surgery, disruption can lead to anaphylactic shock due to exposure to the inside of the cysts.

This is one really good reason why people should be careful handling dog faeces especially if the dog may have eaten a dead sheep.

So what have we learnt from today’s show? Don’t eat dog faeces and if you have hydatid disease don’t let a dog eat your corpse!

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