A Fluke Of Nature You'D Rather Not Meet...

[jsflynn603]

In the Chiang Mai forum someone had asked if it was safe to eat fish from the Ping River and so I wrote the following. I thought it might be useful to those who come here to read about health issues in Thailand.

Thailand has one of the worst problems with Liver Flukes in the world, though you hear little about it. Adventurous travelers in the North and North East of Thailand may come across the common dish known as Koi Pla, yet it is very wise to avoid this dish as most Thai who make it think that they know how to destroy the parasites in it, yet the fact is, that Thai research shows that they don't!

Liver fluke cercariae (a parasite whose live cycle involves a certain snail and then fish (though, in a pinch---humans work just fine) infest most waters around Chiang Mai. The moat around Chiang Mai is absolutely rife with liver fluke cercariae, so much so that if you were to use a bucket to water lettuce that you were growing and then ate the lettuce, there is no doubt that, in time, you would develop liver flukes, which can cause serious disease and sometimes death. Many villagers who live along the Ping river routinely show cercariae in fecal testing.

In the North, a common fish delicacy is raw fish that is marinated in a vinegar (Koi Pla) and which the local people believe that the marinating kill any liver fluke cercariae. Well, in fact, if the fish is cut properly and marinated for two days in vinegar of appropriate acetic acid content, they are right. Unfortunately for them and for any adventurous farang many locals believe that a few hours of marinating is sufficient and sadly, it is not.

Outside of the cities, in rural villages (including villages on the Ping river) the rate of infected population often exceed 16%, in the Northeast there are areas where 70% of the entire population are infected with liver flukes.

Though liver flukes generally do not kill you, and for some there are few if any symptoms, but for others the symptoms can be serious and they do put you at risk for certain malignant liver cancers. Thailand is one of three countries in the world with the most cases of this often fatal cancer.

Cooked fish, cooked to 160 degrees is safe but if you are cooking, be careful to avoid accidental, even very minor, water or fish contamination of food or drink. The cercariae are too tiny to see.

The life cycle goes from fish to human (or other carnivores). Within the human the cercariae turn into meta-cercariae, which live in the liver and bile ducts and release eggs which are released via feces into water. The eggs are eaten by many types of common snails, the eggs turn into cercariae and are released into river/ponds etc. The cercariae are free swimming and they bore into the fins and flesh of many types of fish, and so the life-cycle goes round and round and "we" are integral to it.

It used to make me cringe a bit to see kids splashing around in SW corner of the moat.

[tim armstrong]

Thanks for a very informative article. I know about liver fluke in other animals, ie sheep, but had no idea about the fish connection. We live much further south on the Ping river,near Nakhon Sawan, and we do eat a lot of local fish, so I will be more aware now about the risks. In my ignorance I had assumed that as most local fish look very healthy, even from canals, that they were fairly free from disease, and probably safer than pork or chicken, but maybe not. Regards.