Monday, 8 November 2010

How Do You Get Chinese Liver Fluke?

To someone in the industrialized world, the chances of getting Chinese liver fluke, Clonorchis sinensis, often seem remote, especially if you consider the life cycle of the worm.

[caption id="attachment_162" align="aligncenter" width="300" caption="Clonorchis sinensis life cycle. CDC"][/caption]

Eating raw fish will do it, if the fish has the parasite in its tissues, and with sushi becoming more and more popular, this is believable. But how does the fish get Clonorchis? In order for everything to come together for the worm, an infected person has to defecate in fresh water where the correct species of snail is resident. If the snail eats the worm eggs in the feces it, in turn, is infected. After multiplying in the snail, the parasite leaves of its own accord and burrows into the flesh of a fish. The fish must then be caught and eaten raw by a human (you) in order for the parasite to infect another person (who then has to defecate in fresh water…).

That life cycle is so complicated, one wonders how the fluke can possibly continue to exist. In fact, it lives in some 19 million human livers today. Humans owe it all to ourselves: behind every successful human parasite, there’s a human behavior that makes it all possible. In Asia, a cultural love affair with eating raw fish, and the historical habit of building toilets over fish-rearing ponds (to encourage algae growth to feed the fish) helped turn this fluke into a successful fluke.

And did you know that C. sinensis in fish can survive pickling, salting, drying, and smoking?