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
Physical Description
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.
- Other Physical Features
- ectothermic
- bilateral symmetry
Reproduction
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)
- Parental Investment
- no parental involvement
Behavior
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).
- Key Behaviors
- parasite
Food Habits
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)
Economic Importance for Humans: Positive
This animal does not benefit humans.
Economic Importance for Humans: Negative
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).
Conservation Status
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.
- IUCN Red List No special status
- US Federal List No special status
- CITES No special status
Other Comments
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).
Contributors
Sarah Green (author), Fresno City College, Jerry Kirkhart (editor), Fresno City College.
Glossary
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
an organism that obtains nutrients from other organisms in a harmful way that doesn’t cause immediate death
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
scrub forests develop in areas that experience dry seasons.
References
Committee on Infectious Diseases American Academy of Pediatrics, 2000. Red Book . Elk Grove Village, Il: American Academy of Pediatrics.
Hickman, C., L. Roberts, A. Larson. 1997. Integrated Principles of Zoology . New York: McGraw-Hill Higher Education.
Maszle, D. 1996. «Schistosoma Japonica Overview» (On-line). Accessed 3 April 2001 at http://ehs.sph.berkeley.edu/china/sjap.htm.
Roberts, L., J. Janovy Jr.. 2000. Gerald D. Schmidt & Larry S. Roberts’ Foundations of Parasitology, Sixth Edition . Burr Ridge, Illinois: McGraw Hill.
Schistosomiasis
Animal Reservoirs
Schistosoma japonicum is the only species having relevant animal reservoirs that contribute to environmental contamination through daily egg excretion ( Figure 52.4 ). A total of 31 wild mammals and 13 domestic animals have been shown to carry S. japonicum in China, 26 and in the Philippines, cats, dogs, pigs, water buffaloes and rats were found to have a 3–31% prevalence of viable S. japonicum eggs in the stool. 27 In hilly environments of China, where buffalo are less common, dogs appear to be the main zoonotic reservoir, with prevalence of up to 75%. 28 In this setting, inclusion of animal infection prevention as part of schistosomiasis control campaigns has proven a more successful strategy in China. 29
In contrast, humans are effectively the only reservoir host of S. haematobium. The few infections with this parasite found among non-human primates, Arteriodactyla or Rodentia can be considered as incidental and of no epidemiological importance.
S. mansoni infections have been reported in a wide range of mammals (non-human primates, Insectivora, Arteriodactyla, Marsupilia, Rodentia, Carnivora and Edentata). However, evidence implicating their role in maintenance of transmission of the parasite is, with two exceptions, lacking. In one focus in Tanzania, it is believed that baboons maintain the parasite among themselves, 30 and there is good reason to believe that the local strain of S. mansoni is maintained by both rats (Rattus rattus – a known reservoir host) and by humans in the natural habitat of Guadeloupe Island 31,32 and in some areas of Brazil. For S. mekongi in Cambodia, among local fauna, only dogs have been found to harbour parasite eggs in a recent survey. 33
Lesi yang dihasilkan oleh Schistosoma japonicum sma dengan Schistosoma mansoni maupun Schistosoma haematobium. Dalam hal ini organ yang terutama mengalami kerusakan adalah usus dan hepar. Berat ringannya infeksi tergantung dari jumlah cacing.
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Stadium inkubasi (4 – 7 minggu)
Saat penetrasi cercaria melalui kulit kemudian migrasi melalui sirkulasi darah sampai tumbuh menjadi cacing dewasa. Gejalanya dapat berupa :
- Pada kulit : hanya reaksi lokal yang ringan, pada jaringan kulit terjadi infiltrasi selluler. Spesies non manusia dapat menimbulkan dermatitis cercaria (swimmer’s itch)
- Pada paru-paru : terjadi rangsang traumatis dan infiltrasi, kadang-kadang dengan haemorrhage, gejala batuk-batuk, dan nyeri di dada.
- Pada hati : dapat timbul hepatitis akut selama larva mengalami pertumbuhan di dalam cabang-cabang vena portae dalam hepar. Pada stadium sistemik ini akan terjadi gejala panas, menggigil, sakit kepala, leukositosis, dan eosinophilia.
Schistosoma mansoni
| A | B |
A, B: Huevos de Schistosoma mansoni en un paciente de Egipto. Estos huevos son largos (de 114 a 180 �m de longitud) y presentan forma caracter�stica, con una espina lateral prominente cerca del extremo posterior. El extremo anterior est� achatado y ligeramente curvado. Cuando los huevos son excretados, contienen al miracidio maduro (especialmente visible en A).
| C | D |
C, D: Huevos de Schistosoma mansoni mostrando la espina lateral caracter�stica.
| E | F | G |
E: Huevo de Schistosoma mansoni (lugol).
F: Huevos de Schistosoma mansoni (frotis directo).
G: Huevo no viable de Schistosoma mansoni.
Schistosoma japonicum
| H | I |
H, I: Huevo de Schistosoma japonicum. El huevo es t�picamente oval o subesf�rico y presenta una espina vestigial, que se observa mejor en la imagen I. Los huevos de Schistosoma japonicum son m�s peque�os (de 68 a 100 �m por 45 a 80 �m) que los de otras especies.
| J | K |
| L | M |
J, K, L, M: Los huevos de Schistosoma japonicum. En las im�genes J, K y L la espina no se distingue. Los huevos en la imagen M muestran una espina visible.
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