Schistosoma japonicum
bilharzia
(Also: blood fluke)

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

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

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.

See other sections for life-cycle information. This species has an array of chemical sensing organs that help locate hosts. The free-swimming stages (miracidium and cercaria) swim vigorously, struggling to find a host. Cercaria tend to swim to the surface of the water they are in, sink down, and then swim up again (Roberts and Janovy 2000).

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)

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.

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.

This species is one of three (the others are S. haematobium and S. mansoni) that cause schistosomiasis. They are a major cause of human illness and suffering in the tropical regions of the world.

Schistosome infection can be diagnosed by checking for eggs in the feces, by biopsy of the liver or bladder, and by serological tests for schistosome antigens. Chemical treatment using the drug praziquantel has a high degree of success. Unfortunately millions of people are infected with schistomes every day due to exposure to contaminated water. Efforts to control this disease are ongoing, but it has proved difficult to eliminate. At this time there is no vaccine for schistosomes. (see Roberts and Janovy, Maszle, Toyoda, WHO below).