The Asian liver fluke Opisthorchis viverrini is a parasitic worm that causes disease in millions of people living in Asia. It is also linked to a fatal cancer of the bile duct. Now by decoding its genome, an international team led by the University of Melbourne in Australia hopes to spur new ways to fight a parasitic infection for which there are few available treatments.
In the journal Nature Communications, the scientists describe how they assembled and characterized the largest parasitic worm genome studied to date.
Lead author Dr. Neil Young, of Melbourne’s Faculty of Veterinary Science, says the study helps us understand how the tiny worms survive the hostile environment of the human bile duct, and “provides further evidence that these parasites release proteins that directly alter human tissue.”
The Asian liver fluke Opisthorchis viverrini is a tiny parasitic worm carried by snails and fish. It infects humans and dogs and cats through the ingestion of raw or undercooked fish.
Once ingested, the parasite travels to the bile duct – a tube that carries fat-digesting fluid secreted by the liver to the intestine – where it causes a range of chronic liver and gall bladder diseases, including cancer.
The International Agency for Research on Cancer (IARC) classes O. viverrini as a group 1 carcinogen and a significant risk factor for cholangiocarcinoma – a deadly cancer of the bile duct.
Although the incidence of the cancer is low in Western countries, it is prevalent in many parts of South East Asia, say the researchers, who note current estimates show infection by the parasite amounts to some 10 million people worldwide, and in Asia, cancer linked to O. viverrini is detected in around 2,500 people a year.
There is currently no vaccine against the parasite, and treatment relies on the use of a single drug, praziquantel. But over-use of the drug can reduce its effect and lead to inflammation; plus, even after effective treatment, reinfection is frequent.
The authors believe the genome sequence released in the study will help underpin deeper explorations of cancer-causing parasites, increasing the likelihood of new treatments against parasites and parasite-induced cancers.
For example, they have characterized the behavior of some of the parasite’s genes, shedding light on some of the worm’s fundamental molecular biology. They identify some of the key pathways through which the parasite exploits the host environment, and they predict some of the genes that may lead to cancer.
The authors note that the study should also fill some gaps in our knowledge of liver fluke parasites, as a lot of genetic studies have tended to focus on blood flukes or schistosomes.
In November 2013, Medical News Today learned how researchers in the US have identified drug-resistance mutations in a blood fluke parasite that affects some 187 million people in South America, Africa and Asia. The team said the achievement – made possible by the publication in 2009 of the schistosome genome – will be of great help in fighting a parasite that is second only to malaria in terms of mortality.