Epidemiology
Reservoir hosts of Paragonumus spp. include numerous species of carnivores including felids, canids, viverrids, mustelids, some rodents and pigs. Humans become infected after eating raw freshwater crabs or crayfish that have been encysted with the metacerciaria. Southeast Asia is more predominately more infected because of lifestyles. Raw seafood is popular in these countries. Crab collectors string raw crabs together and bring them miles inland to sell in Taiwan markets. These raw crabs are then marinated or pickled in vinegar or wine to coagulate the crustacean muscle. This method of preparation does not kill the metacercariae, consequently infecting the host. Smashing rice-eating crabs in rice paddies, splashing juices containing metacercariae, can also transmit the parasite, or using juices strained from fresh crabs for medicinal uses. This parasite is easily spread because it is able to infect other animals (zoonosis). An assortment of mammals and birds can be infected and act as paratenic hosts. Ingestion of the paratenic host can lead to infection of this parasite.
Paragonimus westermani is distributed in southeast Asia and Japan. Other species of Paragonimus are common in parts of Asia, Africa and South and Central America. P. westermani has been increasingly recognized in the United States during the past 15 years because of the increase of immigrants from endemic areas such as Southeast Asia. Estimated to infects 22 million people worldwide.
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