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Schistosoma mansoni

By Lisa Moen and Jessica Tkacs

Geographic Range

Schistosoma mansoni is found throughout Africa and South America, especially in Brazil, Venezuela, Surinam and Guyana. It also lives on several Caribbean islands such as Puerto Rico, St. Lucia, Martinique, and Guadeloupe. It is thought that the species may have been brought to the Western Hemisphere during the African slave trade when a number of susceptible snail hosts may have been introduced, possibly in the casks of drinking water that were brought with the slaves. (Bogitsh, et al., 2005)

Habitat

Schistosoma mansoni adults are parasitic to humans and commonly reside in mesenteric venules and in the large intestine. During development, the miracidium larvae live in fresh water habitats in shallow coastal areas before infecting a snail intermediate host. The miracidium transforms into a sporocyst in the headfoot of the snail, and then moves to the digestive glands or gonads. Cercariae leave the sporocyst through a birth pore, pass through the tissues of the snail, then are released into fresh water before entering a human. (Bogitsh, et al., 2005; Meyer and Olsen, 1971)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Schistosoma mansoni is a parasitic flatworm. An oral sucker surrounds the mouth of the adult, and a ventral sucker is immediately located posterior to the bifurcation of the gut. There is an esophagus with distinct esophageal glands, but no pharynx is present. Paired caeca come together posteriorly, forming a single caecum that extends the remaining length of the schistosome body. Schistosoma mansoni is dioecious and sexually dimorphic. The adult male (up to 10 mm in length) is more robust than the female and possesses a body groove called a gynaecophoral canal. The female, which is longer and more slender than the male (up to 10 to 14 mm in length), is held within the groove of the male. The tegument of males have tubercles on the dorsal surface, whereas the tegument of females is smooth. The male has 6 to 9 testes, and the male genital pore opens ventrally, immediately posterior to the ventral sucker. On the female, a single ovary is located in the anterior portion of the body. The uterus can be long or short, depending on the position of the ovary relative to the female genital pore. (Bogitsh, et al., 2005)

  • Sexual Dimorphism
  • male larger
  • Range length
    10 to 14 mm
    0.39 to 0.55 in

Development

Adults of Schostosoma mansoni live in mesenteric veins which drain the intestine of the host. The female will generally move to smaller venules before depositing her eggs. The enclosed miracidium is under-developed at time of oviposition, but will be well-formed before reaching the lumen of an infected organ. The egg must penetrate and traverse multiple tissues and mucosal lining before entering the lumen of the gut or the bladder to escape to the environment. The passage of eggs from the blood stream to the lumen of the infected organ are induced by secretions that are part of the immune response of the host. Once the egg has reached the intestinal lumen, the egg can exit the host organism in either feces or urine.

Upon reaching fresh water, the miracidia are activated to hatch, because they are no longer under the inhibitory osmolarity of the host's body fluids. Hatching occurs by rupturing the eggshell along the suture line. Free-swimming miracidia must find a suitable intermediate snail host quickly after hatching, or they will die. After a snail is penetrated, transformation into a sporocyst occurs in the headfoot. Another generation of sporocysts is produced, and these sporocysts migrate into the digestive gland or gonads. Cercariae exit the sporocyst through a birth pore and can be passed to the exterior. This passage is facilitated by secretions coming from a pair of escape glands in the cercaria.

Actively swimming cercariae possess distinctive forked tails and move in a figure-eight pattern. Secretions from the mammalian skin stimulate the cercariae to attach and penetrate the definitive host. Cercariae have five pairs of unicellular glands. Two preacetabular glands are anterior to the ventral sucker, while three postacetabular glands lie behind the ventral sucker. Each gland has a duct that empties at the anterior region of the oral sucker. Cercariae adhere using both their muscular suckers and mucoid secretions to attach to the skin of a human host. Because secretions from the preacetabular glands are highly enzymatic, they facilitate lysis of the host skin for penetration. Within the skin, cercariae burrow into the peripheral capillary bed or enter the lymphatic system, where the worms can migrate to the heart and enter the lungs. Three significant morphological changes occur in cercariae during the penetration process: loss of the tail, loss of the surface coat, and emptying of the contents of the penetration glands. The cercaria is referred to as a schistomule following this transformation.

Schistomules reside within pulmonary capillaries by the third day after penetration. On day four, juveniles begin feeding on host blood cells, which triggers a period of rapid growth and development. After 7 to 10 days, schistomules migrate through the pulmonary vein into the heart, and then into the systemic circulation. About three weeks later, the worms reach the hepatic portal veins, where sexual maturity is reached, and mating is possible after 40 days. Males that contain females in their body grooves move to venules at the definitive sites. (Bogitsh, et al., 2005)

Reproduction

Schistosoma mansoni is a dioecious species, with the male and female individuals being separate. Females spend much of their time wrapped inside the body groove of male worms, resulting in near constant mating. (Bogitsh, et al., 2005; Harrison and Bogitsh, 1991)

Female worms deposit 190 to 300 eggs daily, each measuring 114 to 175 micrometers long by 45 to 68 micrometers wide and bearing a prominent, lateral spine. At the time of fertilization, the sex of worms is genetically determined. (Bogitsh, et al., 2005)

  • Breeding interval
    Schistosoma mansoni breeds daily.
  • Breeding season
    Schistosoma mansoni breeds year round.
  • Range number of offspring
    190 to 300
  • Average age at sexual or reproductive maturity (female or asexual)
    21 days
  • Average age at sexual or reproductive maturity (male)
    21 days

There is no parental investment after the eggs are released. Post-hatching, the free swimming miracidia are on their own to penetrate a suitable snail host within a few hours or they will die. (Bogitsh, et al., 2005; Harrison and Bogitsh, 1991)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Once a schistosome enters the snail intermediate host, development requires 3 to 4 weeks on average. In the human host, the organism will generally live another 7 to 8 weeks. On average, Scistosoma mansoni lives about 80 days. (Bogitsh, et al., 2005)

  • Average lifespan
    Status: wild
    80 days

Behavior

Schistosoma mansoni is a parasite that has both an intermediate and a definitive host. In most cases, the intermediate host is a freshwater snail from the genus Biomphlaria, and the definitive host is a human. Most commonly these parasites infect a human host by piercing the skin and moving into the blood stream. The parasites, as miracidium larvae, are motile and can swim, allowing them to search for an intermediate host. Cercariae are also motile, as they swim from their intermediate snail hosts to their definitive host. Adults remain within the host, with males and females often together as a mating pair, with the female residing in a groove in the body of the male. (Cameron, 1962; Chandler, 1961; Weil and Kvale, 1985)

Home Range

Adults remain within the host. Miracidia and cercariae are free-swimming, but likely do not swim far from areas with potential hosts. (Cameron, 1962; Chandler, 1961; Weil and Kvale, 1985)

Communication and Perception

Schistosoma mansoni communicates through chemical means. Individuals have several receptors, including several ligand-gated channels that respond to chemical changes in the internal environment of their host. Once inside of their host, intermediate or definitive, they are not known to make many changes to its chemistry, but they are thought to protect themselves from localized immune system signals and enzymatic activity by releasing their own signals that lessen or weaken the signals of the host. Individuals live independently in freshwater during the miracidium stage for a short time. Under this condition, the parasite is sensitive to temperature and pressure changes. (Berriman and El-Sayed, 2009; Verjovski-Almeida, 2003)

Food Habits

As a parasite, the dietary needs of Schistosoma mansoni are almost solely fulfilled by the host. The parasite mainly gains nourishment from the blood of the host, feeding on proteins and monosaccharides. Specifically, Schistosoma mansoni consumes a lot of glucose, which the parasite uses to generate energy that it requires for reproduction and other activities. If the host is malnourished, then there are negative effects on the development of the parasite. For example, males of Schistosoma mansoni have been known to have smaller testes when found in a malnourished host than when found in a well-nourished host. Similarly, the ovaries of females are smaller and less abundant when in a malnourished host. (Cameron, 1962; Neves, 2001)

  • Animal Foods
  • mammals
  • mollusks

Predation

Predation on snails (genus Biomphlaria) that are infected with Schistosoma mansoni is not uncommon, but direct predation on the parasites themselves is not widely known. It has, however, been noted that free-living miracidia (prior to infecting a snail) are often preyed upon by certain annelids like those of the genus Chaetogaster. (Wajdi, 1964)

Ecosystem Roles

Individuals of Schistosoma mansoni are found in freshwater environments. Location and distribution vary depending on region and time of year. They are predominantly found in bodies of fresh water with irrigation systems, because the environment remains generally stable. Because they are parasitic, they infect other species in the bodies of water in which they dwell. Most often, they initially infect snails in the family Planorbidae, particularly of the genus Biomphlaria. Other organisms such as monkeys, rats, and other rodents, can be infected themselves by ingesting infected snails. Humans tend to become infected through contact with contaminated water rather than by consumption of infected snails. (Weil and Kvale, 1985)

Species Used as Host

Economic Importance for Humans: Positive

Schistosoma mansoni was one of the first flatworms to have a fully mapped genome, thus allowing much genetic research about the disease schistosomiasis and its prevention/cure. By creating so many research opportunities, Schistosoma mansoni has inadvertently stimulated the economy. (Berriman and El-Sayed, 2009)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

Schistosoma mansoni is the parasite responsible for schistosomiasis, a disease that affects nearly 300,000,000 people. Early on, the disease causes rashes, fever, and muscle aches, while chronic infections can lead to bladder cancer, damaged organs, and in children it can cause developmental issues. In regions where rate of infection is high, over $3,000,000 in medical costs can be made annually to help those infected. Humans become infected through contact with contaminated water, and often in regions of high infection there is little knowledge and education of these parasites. Prevention is costly for those attempting to create cleaner freshwater environments. For many regions, freshwater irrigation systems are a way of sustaining life, and for most of these regions there is not much capital to spare. Cleaning and filtering irrigation systems is expensive and thus cannot happen in most areas. (Center for Disease Control, 2012; Chandler, 1961; Weil and Kvale, 1985)

Conservation Status

Schistosoma mansoni has no special conservation status.

Contributors

Lisa Moen (author), The College of New Jersey, Jessica Tkacs (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Angela Miner (editor), Animal Diversity Web Staff.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

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.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

year-round breeding

breeding takes place throughout the year

References

Berriman, M., N. El-Sayed. 2009. The genome of the blood fluke Schistosoma mansoni. Nature Genetics, 400: 352-358.

Bogitsh, B., C. Carter, T. Oeltmann. 2005. Human Parasitology. Burlington: Elsevier Academic Press.

Cameron, T. 1962. Parasites and Parasitism. London: Methuen.

Center for Disease Control, 2012. "Parasites - Schistosomiasis" (On-line). Center for Disease Control. Accessed April 11, 2013 at http://www.cdc.gov/parasites/schistosomiasis/.

Chandler, A. 1961. Introduction to Parasitology. New York: Wiley.

Harrison, F., B. Bogitsh. 1991. Microscopic Anatomy of Invertebrates. New York: Wiley-Liss Inc..

Laverack, M., J. Dando. 1974. Essential Invertebrate Zoology. New York: Halsted Press.

Meyer, M., O. Olsen. 1971. Essentials of Parasitology. Dubuque, Iowa: Wm. C. Brown Company Publishers.

Neves, R. 2001. Morphological aspects of Schistosoma mansoni adult worms isolated from nourished and undernourished mice: a comparative analysis by confocal laser scanning microscopy. Mem Inst Oswaldo Cruz, 96.7: 1013-1016.

Verjovski-Almeida, S. 2003. Transcriptome analysis of the acoelomate human parasite Schistosoma mansoni. Nature Genetics, 35: 148-157.

Wajdi, N. 1964. The predation of Schistosoma mansoni by the oligochaete annelid Chaetogaster. Journal of Helminthology, 38: 391-392.

Weil, C., K. Kvale. 1985. Current research on geographical aspects of schistosomiasis. Geographical Review, 75: 186-216.

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