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)
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)
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)
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)
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)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
Predation on snails (genus Biomphlaria) that are infected with 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)
Individuals of 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)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
has no special conservation status.
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.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the southern part of the New World. In other words, Central and South America.
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.
an animal that mainly eats meat
an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).
uses smells or other chemicals to communicate
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
mainly lives in water that is not salty.
fertilization takes place within the female's body
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
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).
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.
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
reproduction that includes combining the genetic contribution of two individuals, a male and a female
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).
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
breeding takes place throughout the year
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