Human parasites can cause fatal liver cancer

SYDNEY - Human liver fluke can bring on one of the most fatal forms of liver cancer by secreting granulin, a hormone known to trigger unbridled cell growth.

Michael Smout and Alex Loukas from the Queensland Institute of Medical Research (QIMR) say they are excited by the discovery which shows that a growth hormone from a parasite can affect human cells.

It has been known that certain proteins secreted by O. viverrini (liver fluke) cause cell growth; however, the identity of the protein was unknown. We also knew that the parasite secreted granulin but we did not know that it could affect the human cells around it, said Loukas.

The International Agency for Research on Cancer classifies the human liver fluke as a Group I Carcinogen, meaning that it is a proven cause of cancer of the bile ducts.

This discovery leads the way to a better understanding of how this parasite causes such a devastating form of cancer, said Loukas.

In northern Thailand, where the liver fluke is most common, more than seven million people are infected at any given time.

While less than one percent infected with other carcinogenic pathogens (such as H. pylori and human papilloma virus) develop cancer, as many as 17 percent infected with O. viverrini could develop cholangiocarcinoma, a fatal form of liver cancer.

Previously, it was thought that cholangiocarcinoma was caused by the physical damage brought about by the fluke feeding on cells lining the bile ducts, as well as a diet high in nitrosamines from fermented fish (a native dish of Thailand).

It is now thought that the granulin secreted by the parasite is a major contributing factor to developing bile duct cancer, says a QIMR release.

The study was conducted by the universities of Queensland, Khon Kaen (Thailand) and George Washington, US.

The findings were published in the open-access Public Library of Science Pathogens.