Leucochloridium paradoxum | |
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Leucochloridium paradoxum, parasite in Succinea putris | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Platyhelminthes |
Class: | Trematoda |
Order: | Diplostomida |
Family: | Leucochloridiidae |
Genus: | Leucochloridium |
Species: | L. paradoxum |
Binomial name | |
Leucochloridium paradoxum | |
Leucochloridium paradoxum, the green-banded broodsac, is a parasitic flatworm (or helminth). Its intermediate hosts are land snails, usually of the genus Succinea . The pulsating, green broodsacs fill the eye stalks of the snail, thereby attracting predation by birds, the primary host. These broodsacs visually imitate caterpillars, a prey of birds. [2] The adult parasite lives in the bird's cloaca, releasing its eggs into the faeces.
The species in Leucochloridium share a similar life cycle. [3] [4] They are parasites of snails and birds. This is a truncated life cycle compared with typical trematodes, because the snail acts as both the first and second intermediate host. [5]
Eggs ingested by the snail hatch into miracidia, which develop in the snail's hepatopancreas into the next stage, a sporocyst. The mature sporocyst consists of a number of branches spreading through the haemocoel and may make up a fifth or more of the snail's weight. [6] Some of the branches develop into long tubes ending in a swollen broodsac, but these are staggered in their states of development, so that normally only 2 or 3 are mature simultaneously. [7] One or both of the snail's tentacles become occupied by a mature broodsac, which transforms the appearance. The tentacle is swollen and the pulsating, colourful, banded broodsac visible inside mimics the appearance of an insect larva like a caterpillar. This encourages their consumption by the next host, insectivorous birds. Observations in captivity indicated that birds tore the broodsac out of the snail before eating it, [8] so the snail may survive this. Birds may also become infected by eating broodsacs that have spontaneously burst from the tentacle, surviving for an hour whilst they continue to pulsate. [7] [9] [10]
At their base, [11] the sporocysts produce asexually many tail-less cercariae, which develop directly into metacercariae within the sporocyst, depositing a thick mucoid coat around themselves. The mature metacercariae are oval in shape, 1.2 × 0.8 mm; typically 100–250 such metacercariae accumulate in a broodsac. [11] If the broodsac is eaten by a bird, the metacercariae pass along its alimentary tract, and lodge in the cloaca. Having lost the mucoid coat, they develop into adult distomes, c. 1.5 mm long. This form has two suckers on the ventral side, which anchor it to the cloacal wall, and a smooth dorsal surface. The adults are hermaphroditic and release eggs into the bird's faeces. Some will be eaten by a snail, thus completing the life cycle. [9] [10]
In a study in Russia, snails became infected in spring and summer. The resultant sporocysts were producing infective metacercariae in the following spring but then died in late summer. [7] The lifetime of the adult stage in its bird host is believed to be of the order of weeks or months. [12]
The pulsations of the broodsacs typically vary from 40 to 75 times a minute depending on temperature, but they cease in the dark. [6]
The parasite manipulates the snail host's behaviour in a way likely to make it more conspicuous to birds. In one study of Succinea putris hosts, infected snails stayed in better lit places for longer, sat on higher vegetation, and were more mobile. Whereas 53% of infected snails remained fully exposed for the 45 minutes of the observation period, the figure was only 28% for the controls (nearby snails without Leucochloridium broodsacs). [2] Infected snails may survive for at least a year and continue to be able to use the eyes on the ends of their tentacles. [6] Although snails infected by other Leucochloridium species are reported to continue to reproduce, [3] snails infected by L. paradoxum often show a reduction of the sexual organs. [6]
The appearance and behaviour of the sporocysts is a case of aggressive mimicry, where the parasite vaguely resembles the food of the host, thereby gaining the parasite entry into the host's body by being eaten. This is unlike most other cases of aggressive mimicry, in which the mimic eats the duped animal. [13]
In older literature, L. paradoxum may be referred to as L. macrostomum, derived from Rudolphi's 1803 description of Fasciola macrostoma, which he later (1809) renamed Distomum macrostomum. Zeller (1874) misidentified specimens of L. paradoxum as D. macrostomum. Rudolphi's species is now in the genus Urogonimus. [14] Leucochloridium heckerti Kagan, 1951 is also considered a synonym of L. paradoxum. [9]
The easiest way to differentiate between Leucochloridium species is from the appearance of the broodsacs in the tentacle of the host snail. Leucochloridium paradoxum exhibits broodsacs that have green bands with dark brown and black spots, and with a dark-brown or reddish-brown tip. [9] [6] Nowadays this method of identification may be supported with ribosomal DNA sequences. [12] A snail may be simultaneously infected by more than one species of Leucochloridium. [15]
The adults, found in the cloaca of birds, are less well known, so that distinguishing the species is less straightforward. [12]
Leucochlordium paradoxum is found in moist areas, such as marshes, where the usual intermediate host Succinea snails are found.
Leucochloridium paradoxum was originally described based on its sporocyst stage, collected from an island in the river Elbe at Pillnitz, near Dresden, Germany. [1] Other known locations are Poland, Belarus, the Saint Petersburg area of Russia, Denmark, Sweden, Norway, the Netherlands, the United Kingdom and Japan. [12] [15] [9] [16] It is believed to be the species of Leuchochloridium infecting an endemic species of semi-slug on Robinson Crusoe Island in the Pacific, the only record from the Southern Hemisphere. [17]
Intermediate hosts:
Hosts:
Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.
Digenea is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults commonly live within the digestive tract, but occur throughout the organ systems of all classes of vertebrates. Once thought to be related to the Monogenea, it is now recognised that they are closest to the Aspidogastrea and that the Monogenea are more closely allied with the Cestoda. Around 6,000 species have been described to date.
Trematodes are parasitic flatworms of the class Trematoda, specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions.
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Leucochloridium is a genus of parasitic trematode worms in the order Diplostomida. It Is the sole genus in the family Leucochloridiidae. Members of this genus cause pulsating swellings in the eye-stalks of snails, so as to attract the attention of predatory birds required in the parasites' lifecycle.
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Leucochloridium variae, the brown-banded broodsac, is a species of trematode whose life cycle involves the alternate parasitic infection of certain species of snail and bird. While there is no external evidence of the worm's existence within the bird host, the infection of the snail host is visible when its eye stalks become grotesquely engorged with the parasite's brood sacs. These brood sacks pulsate and move to imitate insect larva, attracting the parasite's next host, insectivore birds. The bird rips off the eye stalk and eats it, thus becoming infected. Later on, the parasite's eggs are dropped with the bird's feces. Similar life-histories are found in other species of the genus Leucochloridium, including Leucochloridium paradoxum.
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Echinostoma hortense is an intestinal fluke of the class Trematoda, which has been found to infect humans in East Asian countries such as Korea, China, and Japan. This parasite resides in the intestines of birds, rats and other mammals such as humans. While human infections are very rare in other regions of the world, East Asian countries have reported human infections up to about 24% of the population in some endemic sub-regions. E. hortense infections are zoonotic infections, which occurs from eating raw or undercooked freshwater fish. The primary disease associated with an E. hortense infection is called echinostomiasis, which is a general name given to diseases caused by Trematodes of the genus Echinostoma.
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