Chinese Liver Fluke, Clonorchis sinensis

The Chinese liver fluke (Clonorchis sinensis) is a species of parasitic worm that is classified within the Platyhelminthes phylum. It can be found in Southeast Asia, Taiwan, Japan, and China and is present in nearly 30,000,000 humans today. It is thought to be one of the world’s most pervading parasites.

The Chinese liver fluke requires two intermediate, or secondary, hosts and one definitive, or main, host to successfully complete its lifecycle. The first intermediate host is typically the snail Parafossarulus manchouricus, although other snails like Tarebia granifera and Melanoides tuberculata can also be used. Once the eggs penetrate the flesh of the freshwater snail, they will develop into miracidium, which further develop into sporocysts that can form “daughter” redia. After this stage, cercaria larvae are formed. These larvae will penetrate the flesh of the snail once more, moving into the water where they will locate a fish to use as the second intermediate host. Once the larvae have entered the flesh of the fish host, they will develop into a metacercarial cyst, which protects them until they can be consumed by their definitive host, which is typically a human. The protective cyst allows the larvae to travel through a human’s acidic stomach into the small intestine without being digested. After detaching from the cyst, the larvae will move though the bile tree into or near the liver, where they will feed of the bile of the host and mature. Once the larvae mature into adult flukes, they will reproduce in this area, creating one or more eggs every thirty seconds.

Although many human hosts of the Chinese liver fluke show no symptoms of an infection in early stages, they can start showing symptoms in the acute phase. These include nausea, diarrhea, and abdominal pain. After longer periods of infection, symptoms can include abdominal discomfort, fatigue, weight loss, jaundice, inflammation, bacterial infections, and hyperplasia, which is an inflammatory reaction caused by the presence of the parasite. In some cases, the human host can contract cholangiocarcinoma. This parasite may also cause complications by consuming all of the bile that the liver produces while it is maturing, and by creating a blockage of the bile if the eggs build up.

When diagnosing a Chinese liver fluke infection, most experts use a microscope to locate eggs within a stool samples or duodenal aspirate. Once the species has been distinguished from other species of parasitic worm, medicines can be used to treat the infection. These include mebendazole, bithionol, albendazole, praziquantel, and triclabendazole.

Image Caption: Clonorchis sinensis. Credit: Kelidimari/Wikipedia (CC BY-SA 3.0)