Most studies on Echinostoma malayanum have occurred in the Asian tropics, with most cases of infection documented in countries such as Thailand and the Philippines. The first characterization of the species occurred in Singapore. Infections have been reported as far as in India and South Korea. (Belizario, et al., 2007; Chai, 2008; Hortle, 2008; Joe, 1963; Kumar, 1998; Maji, et al., 1993)
Common distribution is localized to Southeast Asia in particular, especially in Thailand, Malaysia, Cambodia, Singapore, and the Philippines. (Kumar, 1998)
The habitat of the trematode fluke, Echinostoma malayanum, is mostly confined to brackish or freshwater. The first form of the fluke, which infects snails, is commonly found in fish ponds that are frequently fertilized by human feces, where eggs are passed. Infected snails are also found in shallow, weedy waters such as rice paddies. Infected fish or mollusks, which are the second intermediate hosts, are found in rivers and ponds in tropical habitats, where they are caught and consumed by humans. (Belizario, et al., 2007; Fried and Graczyk, 2000; Graczyk and Fried, 1998; Kumar, 1998; Mohandas and Nadakal, 1978)
In the intermediate host snail, E. malayanum metacercariae were gathered from the host's kidneys, pointing to a possible place of encystment. Frogs have also been found with the metacercariae in their kidneys, and serving as a second intermediate host. (Mohandas and Nadakal, 1978)
The adult worm resides in the bowels of the definitive host, which can be a human or other vertebrate such as a dog. The definitive host is the vertebrate animal which consumes the undercooked or raw animal in which the metacercariae reside. The flukes develop to adulthood in the definitive host, and produce eggs. (Belizario, et al., 2007; Chai, et al., 2009)
Adult Echinostoma malayanum flukes are flat and elongate shaped, and have a collar of 43 spines that differentiate them from other digenean flukes. The number of collar spines can range between 39 and 45, and are arranged in alternating rows on the dorsal side of the fluke. The spines surround a large oral sucker. The fluke possesses a large pharynx and prepharynx, and has a short esophagus. There is a large ventral sucker present, and the characteristically long cirrus sac reaches beyond the ventral sucker. Echinostoma malayanum is a hermaphrodite, with two large, lobed testes located in the posterior half of the body. The ovaries are pretesticular. (Chai, et al., 2009; Dunne, 2009; Kumar, 1998)
Development of the Echinostoma malayanum and trematodes in general involves many stages. In E. malayanum there are seven stages of development from the egg to the adult, and each stage is very specific.
After being expelled from the body of an adult fluke through the genital pore, the yellow-brown ellipsoidal eggs of E. malayanum are unable to develop in the human body. These eggs are then expelled from the human body through the feces, which is the only known diagnosis of infection by E. malayanum. The eggs cannot hatch until ingested by their first host, a snail of the family Planorbidae or Lymnaeidae.
Once ingested, the eggs hatch into the first stage larva called the miracidium. The miracidium is free swimming in the intestine of the snail host, and after hatching burrows into the intestinal tissue of the host. Morphologically, the miracidium is covered with ciliated plates, which are shed upon burrowing into the intestinal wall.
The parasite then develops into an endoparasitic form known as the sporocyst. The sporocyst exists as a hollow fluid filled germinal sac, which has a birth pore at the anterior of the body. Successive generations of larvae are passed from the birth pore, and these larvae may develop into daughter sporocysts which are identical to the parent, or a second larval stage known as the redia.
Like the sporocyst, the redia is a fluid filled sac. This redia may then develop into a second generation sporocyst, or develop into the last larval stage known as the cercaria. The redia of some trematodes such as E. malayanum exhibit predatory behavior, as they actively seek out redia of other trematode species to feed on.
Cercariae are the final larval stage of the parasite. They resemble the adult form of the fluke, and have the horseshoe collar of spines that the adult E. malayanum will eventually have. Cercariae are strong swimmers, as they leave the body of the first snail host and actively seek out their second intermediate host through a variety of environmental cues. The second intermediate host can be any number of aquatic organisms such as snails, mussels, tadpoles, frogs, and fish. After entering the second intermediate host, the cercariae develop into the resting stage of the parasite, the metacercaria.
The metacercaria resembles the cercariae, and can exist in a large variety of amphibious animals. This increases the chance that the second intermediate host will be consumed by its definitive host. When consumed by the definitive host, the metacercaria will develop into an adult fluke. (Dunne, 2009; Graczyk and Fried, 1998; Hortle, 2008; Pearson, 1959)
Echinostoma malayanum is able to breed all year round, sexually and asexually. The same chemical signals that mediate aggregating in the small intestine of the definitive host may also mediate the pairing of adult flukes. (Dunne, 2009; Fried, et al., 2004; Kumar, 1998; Muller and Baker, 1990; Toledo, 2009)
Being hermaphroditic, E. malayanum is able to fertilize itself. However, the adult fluke is also able to undergo sexual reproduction in the intestine of the definitive host, after around 13 to 23 days of infection. These trematodes possess a pair of testes which contains structures such as the prostate gland, vas deferens, and penis. The testes also share a common genital atrium with the uterus. The uterus contains structures such as the ovary, where eggs are produced, and an oviduct which carries the eggs to the ootype where fertilization eventually occurs. During sexual reproduction, the penis is inserted into the vaginal opening of its mate, but during self fertilization the E. malayanum can just insert the penis into its own vaginal opening.
After fertilization in the ootype, yolk hardens around the egg and the eggs are transported back to the uterus. The eggs leave via the genital pore, and are transported out of the body through the feces. (Dunne, 2009; Maji, et al., 1993; Mohandas and Nadakal, 1978)
There is no known parental involvement after fertilization and eggs are laid. After the eggs exit the body via the genital pore, they expelled from the human body through the feces. After passing out of the human body, the life cycle begins again as they search for a primary host snail. (Dunne, 2009; Hortle, 2008)
Although the specific lifespan of Echinostoma malayanum is unknown, other adult echinostome flukes are known to live for up to 1 year in the human body. (Fried and Graczyk, 2000; Graczyk and Fried, 1998; Hortle, 2008; Kumar, 1998)
Adult flukes of Echinostoma malayanum are obligate parasites of vertebrates such as dogs and humans. No social structures have been elucidated, but adults are known to aggregate in the host's small intestine. Since in vivo studies of E. malayanum are not commonly performed, their behavior is largely unknown. (Belizario, et al., 2007; Dunne, 2009; Fried and Graczyk, 2000)
Miracidia of Echinostoma malayanum possess many sensory organs, and seek out the first intermediate host through a variety of light and gravitational cues. Miracidia use these senses to move to an area where their first intermediate hosts may be located.
Prior to leaving from their first intermediate host, the flukes may use other cues to time their emergence.
The cercaria, which emerge from the first intermediate host, use more advanced senses to locate the second intermediate host. The cercaria possess sensory organs, touch receptors, and eye spots. Cercaria use these senses to locate a habitat that is conducive to finding their next host. Cercaria may use cues such as light or water turbulence to locate the second intermediate host. (Dunne, 2009)
In the adult intestine, chemical signals can mediate the clustering of flukes, which explains how large numbers of the flukes are seen localized in one area of the mucosal membrane. Chemical changes in sites in the upper lumen of the small intestine indicate a specific site of attachment, with mechanical irritation also being a clue. (Belizario, et al., 2007; Chai, et al., 2009; Fried and Graczyk, 2000)
Echinostoma malayanum is an obligate parasite that lives in its host's small intestine. Adult flukes live off of the nutrients in their host's body. They will feed on anything in the intestine, such as blood cells, mucus cells, tissue, and undigested nutrients found in the intestine. The suckers of the fluke attach them to the mucosal layer of the small intestine, which is sometimes eaten away completely. Studies of the buccal cavity of the fluke indicated bits of undigested membrane. In areas where massive amounts of the fluke were observed, complete destruction of the villi and loss of mucosal integrity and ulcerations were observed. (Chai, et al., 2009; Fried and Graczyk, 2000; Mohandas and Nadakal, 1978)
No predators are known for E. malayanum. There is anecdotal evidence that the second larval stage, the redia, exhibit some interspecies predation in the bodies of their hosts, but this has not been supported for E. malayanum. (Lie, et al., 1967)
Echinostoma malayanum is a parasitic species of many other animals. It uses snails of the families Planorbidae and Lymnaeidae as first intermediate hosts. Snails, mussels, tadpoles, frogs, and fish are second intermediate hosts. Finally, definitive hosts are anything which eats the second intermediate hosts, which can include humans, rodents, dogs, and pigs. (Belizario, et al., 2007; Chai, et al., 2009; Hortle, 2008; Kumar, 1998)
As a parasite with no known benefits, Echinostoma malayanum is not known to have a positive economic impact on humans.
Although exact monetary measurements of the impact of Echinostoma malayanum are not available, it is assumed that the true impact is under reported due the prevalence of infection in countries with a low minimum wage and infection in low population, rural areas. Humans infected with echinostomiasis are known to suffer from diarrhea, vomiting, tenesmus, anorexia, urinary incontinence, and loss of weight. Because it harms humans, the trematode fluke is known to lower productivity and raise health care costs. Control programs by the World Health Organization have been implemented. (Belizario, et al., 2007; Chai, et al., 2009; Graczyk and Fried, 1998)
Echinostoma malayanum is not known to be endangered in any area of the world.
Bob Fan (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.
living in landscapes dominated by human agriculture.
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.
areas with salty water, usually in coastal marshes and estuaries.
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.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.
fertilization takes place within the female's body
marshes are wetland areas often dominated by grasses and reeds.
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 the capacity to move from one place to another.
specialized for swimming
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.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
an animal that mainly eats blood
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
breeding takes place throughout the year
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