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Life-cycle[edit]
The lifecycle of Leucochloridium variae is characterized by the infection of a definitive avian host through the ingestion of sporocysts contained in the intermediate Succinea host. Leucochloridium variae primarily live in the cloaca and intestine of their bird host, while the sporocysts live in the hepatopancreas, haemocoel and the ocular tentacles of Succineidae land snails.[1]
Transmission and infection of intermediate snail hosts[edit]
Avian hosts release fluke eggs along with their excreta, which will land on surrounding vegetation for snails to consume. The miracidia will hatch and bore through the snail’s digestive tract. The sporocyst will penetrate and entangle the internal organs of the snail. The sporocysts will continue to grow and multiple by asexual reproduction. The cercariae will develop and encyst in each brood-sac. Brood-sacs will migrate to the snail’s tentacles, where they will mimic the behavior of caterpillars to attract insectivorous birds.[2][3] The growth and reproductive intensity of Leucochloridium variae is regulated at the level of the organism because a single sporocyst can establish a life-cycle within the infected snail. However, snails can be infected by more than one species of Leucochloridium.[4]
Sporocyst Description[edit]
Snails infected with the sporocyst exhibit destined tentacles, which disrupted the snail’s normal ability to retract into their shell. Brood-sacs may contain multiple free floating metacercariae, which will move about in pulsating manor. Light intensity affects the rate at which the brood sacs pulsate. Brood sacs will normally pulsate between forty and eighty times per minute. The pulsating movement is described as an alternation of shortening and lengthening of the brood sac. Brood sacs will not show movement in complete darkness.[5]
Transmission and infection of Avian definitive hosts[edit]
The insectivorous birds are attracted to the pulsating of the metacercariae in the sporocyst. This will cause the birds to attack and ingest the brood sacs located in the snails’ tentacles. After digestion of the broodsac, sporocysts will become cercaria and further develop into adults. Adult Leucochloridium variae are hermaphroditic helminths, but can cross fertilize with other worms if in close enough proximity. The gravid adults will release their eggs into the intestines of the birds to be excreted out with the bird’s feces; thus, continuing the Leucochloridium lifecycle.[6] Intense infection by the worms can lead emaciation and death in birds. Birds may also freeze to death from the lack of adipose tissue.[7]
Gravid Adult Description[edit]
Adult worms are characterized by a flesh-colored body containing an egg-filled uterus that appears black by reflected light. The worms contain a cuticula with a subterminal oral sucker. They also contain a muscular pharynx, ventral sucker, and ceca. The gonads of the worm are arranged in a triangle, containing an ovary with an anterior and posterior testis.[5] The oral sucker is primarily used for the attachment to the avian cloaca. It must withstand the constriction of cloaca, which occurs during defecation. Leucochloridium contains a smooth oral sucker, which functions by forming a tight seal against the host’s mucosa. Leucochloridium also contains a smooth dorsal side, which aids in the decrease of friction of passing stool. The rest of the fluke is covered in microvilli that are used to anchor it to the inside of the cloaca. Leucochloridium variae tegument is considered finely spined.[8]
Behavioral differences in infected intermediate hosts[edit]
Parasites often induce certain behavioral changes in their hosts in order to aid in the transmission and completion of its life cycle. Land snails parasitized by Leucochloridium spp. will experience phenotypic modification through the pulsating brood sacs. Infected snails were found to have increased mobility, which allowed them to migrate to higher and more well let areas. This makes them more susceptible and accessible to avian predation.[9]
Distribution and History[edit]
Different species of Leucochloridium can be found all over the planet, while Leucochloridium variae is specifically found in North America. The first known description of L. variae was written by McIntosh in 1932. L. variae commonly parasitizes Mniotilta varia and has been collected from lakes in the Michigan area.[3][10][11]
References[edit]
- ^ Yamada, Seitaro; Fukumoto, Shin-ichiro (2011-08), Isolation of sporocyst broodsacs of the Genus Leucochloridium (Leucochloridiidae: Trematoda) from the intermediate host, Succunea lauta, in Japan, Graduate School of Veterinary Medicine, Hokkaido University, doi:10.14943/jjvr.59.2-3.101, retrieved 2020-02-27
{{citation}}: Check date values in:|date=(help) - ^ Woodhead, Arthur E. (1935). "The Mother Sporocysts of Leucochloridium". The Journal of Parasitology. 21 (5): 337–346. doi:10.2307/3271943. ISSN 0022-3395.
- ^ a b MCINTOSH, LOIS (1948). "Leucochloridium Sporocysts from the Okoboji Region". scholarworks.
{{cite web}}: CS1 maint: url-status (link) - ^ Ataev, G. L.; Zhukova, A. A.; Tokmakova, А. S.; Prokhorova, Е. E. (2016-08). "Multiple infection of amber Succinea putris snails with sporocysts of Leucochloridium spp. (Trematoda)". Parasitology Research. 115 (8): 3203–3208. doi:10.1007/s00436-016-5082-6. ISSN 0932-0113.
{{cite journal}}: Check date values in:|date=(help) - ^ a b Robinson, Edwin J. (1947). "Notes on the Life History of Leucochloridium fuscostriatum n. sp. provis. (Trematoda: Brachylaemidae)". The Journal of Parasitology. 33 (6): 467–475. doi:10.2307/3273326. ISSN 0022-3395.
- ^ DeLaCruz, David. "Leucochloridium paradoxum". Animal Diversity Web. Retrieved 2020-02-27.
- ^ Okulewicz, A.; Sitko, J. (2012-12-01). "Parasitic helminthes — probable cause of death of birds". Helminthologia. 49 (4): 241–246. doi:10.2478/s11687-012-0045-7. ISSN 1336-9083.
- ^ Bakke, Tor A. (1976). "Functional morphology and surface topography of Leucochloridium sp. (Digenea), revealed by scanning electron microscopy". Zeitschrift für Parasitenkunde. 51 (1): 115–128. doi:10.1007/BF00380533. ISSN 0044-3255.
- ^ Wesołowska, W.; Wesołowski, T. (2014-03). "Do L eucochloridium sporocysts manipulate the behaviour of their snail hosts?: Leucochloridium sporocysts and snail host behaviour". Journal of Zoology. 292 (3): 151–155. doi:10.1111/jzo.12094.
{{cite journal}}: Check date values in:|date=(help) - ^ McIntosh, Allen (1932). "Some New Species of Trematode Worms of the Genus Leucochloridium Carus, Parasitic in Birds from Northern Michigan, with a Key and Notes on Other Species of the Genus". The Journal of Parasitology. 19 (1): 32–53. doi:10.2307/3271429. ISSN 0022-3395.
- ^ Lewis, Paul D. (1974). "Helminths of Terrestrial Molluscs in Nebraska. II. Life Cycle of Leucochloridium variae McIntosh, 1932 (Digenea: Leucochloridiidae)". The Journal of Parasitology. 60 (2): 251–255. doi:10.2307/3278459. ISSN 0022-3395.