History of Discovery

Clonorchiasis has been around for hundreds of years, although it was not recognized and categorized as a parasitic infection until 1874. We do not know how long this worm has infected humans, but according to Dr. Frank Cox, “As it infects a large number of animals including primates we can safely assume that Homo sapiens has always been infected and that we inherited this worm from our primate ancestors.” The earliest historical record of Clonorchiasis dates back to an ancient corpse buried in 278 B.C. in the West Han Dynasty in China.  Our current understanding of the parasite and disease began in Calcutta, India on September 8, 1874.  At that time James McConnell, a professor of pathology and resident physician at the Medical College Hospital in Calcutta, performed an autopsy of a 20 year old Chinese carpenter who had died several hours after admission.  He found a swollen, tense liver and abnormally large bile ducts, which were obstructed by “small, dark, vermicular-looking bodies.”  He dissected and compared these bodies with other liver flukes recognized at the time (Fasciola hepatica and Distoma lanceolatum) and realized that this fluke constituted an entirely new species.  The name given at the time to this new species was Distoma sinense, but it was eventually placed into the Clonorchis genus by Arthur Looss in 1895. 

The second intermediate host (fresh-water fish) was officially discovered by a Japanese zoologist Harujiro Kobayashi, although McConnell theorized at the first autopsy that the disease was caused by contaminated fish.  In 1914, Kobayashi conducted experiments which identified and provided proof for the existence of fresh water fish as the second intermediate host.  He fed cats (which had previously been recognized as a reservoir species) the flesh of fish which carried a type of encysted fluke which he hypothesized was the precursor to clonorchiasis.  At autopsy, these cats all were found to be infected with C. sinensis.  He also showed that cysts were abundant both in the subcutaneous tissues and in the muscles of fish, particularly in the more superficial parts.  By 1965, approximately 80 species of freshwater fish vectors of C. sinensis were identified. 

The discovery of several species of snails as the first intermediate host was achieved by Masatomo Muto in 1918.  He hypothesized that a certain species of snail he collected (Parafossarulus manchouricus) harboured the cercariae of Clonorchis sinensis.  To go about proving this fact, he infected experimental, cyst-free fish which were in turn fed to non-infected dogs (a known reservoir of Clonorchiasis).  These dogs all became infected with C. sinensis, proving that the snail was the primary intermediate host.  Muto also demonstrated that freshwater fish provided a necessary intermediate stage in the development of the parasite by showing that a rabbit (a known reservoir of Clonorchiasis) did not develop Clonorchiasis when infected with cercariae obtained from the snail host. 

(Information obtained from: A History of Helminthology)


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