In east Asia, Eriocheir sinensis is a host of the lung fluke Paragonimus westermani. If an infected crab is eaten uncooked the parasite can infect humans, causing the disease paragonimiasis. This can be fatal if left untreated.
P. westermani is most often encountered in China, Korea, Thailand, the Philippines and Laos, but it can also be found in people that have travelled to susceptible regions. Cases have been reported from many parts of the world, including South America and Africa, but the disease is rarely seen in North America or Europe. A 2005 report put the number of people infected globally at around 22 million.
When Eriocheir sinensis was first reported from the River Thames in the UK in the 1930s, newspapers expressed concern that paragonimiasis could be introduced into Britain. However, this is unlikely as part of the life cycle of P. westermani requires an aquatic snail family that isn't found in Britain.
A recent analysis of mitten crabs sampled from the River Thames over 17 months failed to detect the lung fluke parasite (Stentiford, 2005).