Schistosoma japonicum is one of the three main Schistosoma trematode flatworms that infect humans and cause schistosomiasis (=bilharziasis), the other two being S. haematobium and S. mansoni (in some regions, S. mekongi and S. intercalatum also infect humans and cause schistosomiasis). Other schistosome species, which parasitize birds and non-human mammals, can cause cercarial dermatitis in humans.

The life cycle of S. japonicum and related schistosomes is complex. Eggs are eliminated from a human host with feces or urine. Under optimal conditions, the eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts. The life stages within the snail include two generations of sporocysts and the production of cercariae. Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host, and shed their forked tail, becoming schistosomulae (human contact with water is thus necessary for infection by schistosomes). The schistosomulae migrate through several tissues and stages to their residence in the veins. Adult worms in humans reside in the mesenteric venules in various locations, which at times seem to be specific for each species. For example, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine and S. mansoni occurs more often in the superior mesenteric veins draining the large intestine. However, both species can occupy either location, and they are capable of moving between sites, so it cannot be stated unequivocally that either is found only in one location or another. Schistosoma haematobium most often occurs in the venous plexus of bladder, but can also be found in the rectal venules. The females (7 to 20 mm in length, slightly larger than males) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively.

Various animals--including dogs, cats, rodents, pigs, horses, and goats--serve as reservoirs for S. japonicum. Pathology of S. japonicum schistosomiasis includes: Katayama fever, hepatic perisinusoidal egg granulomas, Symmers' pipe stem periportal fibrosis, portal hypertension, and occasional embolic egg granulomas in brain or spinal cord.

Schistosoma japonicum occurs in the Far East.

(Source: Centers for Disease Control Parasites and Health Website)

Schistosoma japonicum is found in China, Taiwan, the Philipines and Southeast Asia. (Roberts and Janovy 2000, WHO 1996)

Biogeographic Regions: palearctic (Native ); oriental (Native )

These parasitic worms have a complex life cycle with many stages.

The first stage, the egg, is round or oval and very small (about 80 by 60 micrometers), with a very small spur on one end.

The first stage that hatches from the egg is called a miracidium, and is not much bigger then the egg. It is free-swimming,ovoid, covered with cilia, and could easily be mistaken for protozoan. It has a complex of glands at the front end that are used to penetrate the skin of a snail host.

Once inside a snail, the miracidium sheds its skin and cilia, and metamorphoses into a different shape called a sporocyst. This stage has no mouth or gut, it takes its food directly from the snail it lives in. Each sporocyst reproduces asexually -- creating daughter sporocysts. These live and grow inside the snail host, completing another round of asexual reproduction, but this time the offspring have a different structure, and are called cercaria.

S. japonicum cercaria look like tiny flatworms with fishtails. The body is about 200 by 70 micrometers, the long thin tail is another 220 micrometers long, and has two "flukes" called furci that are each about 80 micrometers long. The front end is equipped with an array of glands and other structures for entering a new host. This stage leaves the snail and enters a bird or mammal (including humans) host and then transforms again, shedding it's tail and moving through the bloodstream.

The worm finally matures inside the intestinal veins of a mammal. It grows to about 15 mm in length. Males are shorter and stouter than females, and have a long groove on their underside in which the female (should one arrive) attaches herself. Both sexes have a strong sucker around the mouth, and another called an acetabulum, a little ways further down on the ventral side. The skin of the worms is coated with tiny spines, ridges and sensory organs that are probably involved in helping resist and avoid the host immune system.

This species must have snail and vertebrate hosts to survive. The snails it uses live in warm freshwater streams, ponds, and ditches.

Terrestrial Biomes: forest ; rainforest ; scrub forest

Aquatic Biomes: benthic

The source of the worm's nutrition is the host. The sporocyst stage absorbs nutrition through its skin, taking it directly from the tissues of its snail host. Adult worms feed on blood in the intestinal veins where they live (Roberts and Janovy 2000)

This species reproduces sexually: a male and female worm must mate in the veins of the host before the female can lay eggs (many other flatworms can produce eggs without mating first). Female worms produce enormous numbers of offspring: a single mated pair may release 3,000 eggs per day, and live for over 20 years. Through a complex process involving secretions from the egg and the hosts' immune system, the eggs are moved through the wall of the vein and into the gut or bladder, where they are excreted by the host. Once they are exposed to freshwater the eggs hatch, and the miracidium emerges. This stage lives for only a few hours, and must find a snail in the genus Oncomelania to tunnel into or it will die. Inside the snail it becomes a sporocyst (larva). While in the snail the sporocysts reproduce asexually and become daughter sporocysts. The daughter sporcysts then reproduce asexually again, this time producing cercaria. It is in this stage that they enter humans and other vertebrates. The cercaria emerge from their snail host and swim in the water. If they contact a host, they quickly stick to the skin and shed their tail. Then they secrete digestive compounds that allow them to penetrate the skin of the host and enter the hosts' circulatory system. They transform again, this time into adult worms that live in the veins of the small intestine (all sources)

There are currently no conservation efforts for this animal. Because of its negative effects on humans most efforts are aimed at destruction and containment. The World Health Organization is working on "...controlling morbidity...health education and provision of safe water." (WHO pg 3) The climate in which the flatworm is found dictates the types of control that we are able to exert in an effort to contain and eradicate it.

US Federal List: no special status

CITES: no special status

S. japonicum is a parasite that uses humans as a primary host, and is a major cause of disease in the regions where it lives. Most of the harm it causes is due to the massive number eggs released. These trigger immune responses that in turn cause many health problems. As the eggs move through the host tissues, they cause fevers, weakness, liver and kidney damage, blood in the urine, and abdominal pain. In a few cases the eggs drift in the circulatory system and end up in other parts of the body, including the brain, causing even more severe damage. In places where this species occurs, many rural people are afflicted with this condition, called schistosomiasis (All Sources).

This animal does not benefit humans.