Ribeiroia ondatrae

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Ribeiroia ondatrae
Systematics
Class : Flukes (Trematoda)
Subclass : Digenea
Order : Echinostomida
Family : Psilostomidae
Genre : Ribeiroia
Type : Ribeiroia ondatrae
Scientific name
Ribeiroia ondatrae
( Price , 1931)
Deformed limb pacific tree frog caused by Ribeiroia ondatrae

Ribeiroia ondatrae is a parasitic suction worm whose larvae can attack amphibians and can lead to deformities such as deformed, missing or excess limbs in infected animals.

In 2002, Pieter Johnson of the University of Wisconsin and colleagues from other institutes published research on studies of 12,000 amphibians with malformations in the journal Ecological Monographs (vol. 72, p. 151). In animals infected with the suction worm Ribeiroia ondatrae , encapsulated resting stages, so-called cysts , are found under the skin at the attachment points of the extremities and tail. It turned out that a connection to the deformations could only be established with the extent of the parasite infestation “and not, as previously assumed, a direct connection with the concentration of nitrate , phosphate or pesticides . "The more the amphibian population was infected with Ribeiroia , the more frequent and more serious the malformations."

Life cycle

The main hosts of the adult sucking worm are water birds , with their droppings worm eggs get into the water. After about two weeks, these develop into miracidia that penetrate the host snails (first intermediate host). The larvae develop in ramshorn snails of the genus Helisoma (syn. Planorbella ), especially the common species Helisoma trivolvis , family Planorbidae. There they transform into sporocysts in the host's heart , which release rod larvae (rediae) that migrate into the kidneys, gonads and the anterior part of the midgut gland. Redia can alternatively release daughter redia or cercariae . The snail loses its ability to reproduce (castration) due to the parasite. The cercariae leave the snail, then penetrate the tadpoles , where they form metacercariae, which are encapsulated in cysts by the host (second intermediate host). Metacercarial cysts of the type are approximately 300 to 350 micrometers long. Lateral diverticula of the esophagus of the metacercaria are characteristic of the genus. The cysts interfere with the normal development of limbs, either mechanically or possibly through signaling molecules. The life cycle closes when infected amphibians are eaten by water birds (40 species known as hosts, very rarely further development also takes place in mammals). The metacercarials released from the thin-walled cyst continue to develop into the adult flukes, which are around 1.7 to 2.8 millimeters in length. The worm lives mainly in the glandular stomach (proventriculus) of the host. The investigations under the direction of Pieter Johnson (University of Wisconsin) showed that the number of Helisoma snails at a location is a direct measure of the parasite infestation of the amphibians.

Influences

The exact mechanism of the malformation has not been determined, but it has been suggested that the deformations result from the mechanical destruction of the cells by the encapsulated dormant stages (cysts) within the amphibian larval stage.

It was also found that the parasite is particularly abundant in eutrophic (nutrient-rich) waters. The researchers suspect a connection with various fertilizers and phosphate input. The herbicide atrazine could weaken the immune system in amphibians, making the frogs more susceptible to infections. The influence of pesticides is also examined.

Studies show that the most common sites for malformations in frogs or toads are the hind legs. However, there seems to be a quantity dependency that influences where a deformity can occur: For example, a moderate amount of Ribeiroia ondatrae can affect the front legs of amphibians, while a severe infestation does not affect the front legs but only deformities on the hind legs seems.

Researchers working with Pieter Johnson ( University of Colorado Boulder ) postulated a high level of biodiversity in 2013, protecting amphibians from diseases caused by parasites. The study of 345 ponds has shown that the more mixed the animal world, the healthier it is; H. the more species live in a pond. "In ponds with six different amphibian species, the number of malformed animals was more than half less than in waters with only one species. The transmission rate of the parasite dropped by almost 80 percent."

Further studies have shown that usually only a relatively small part of the snail population in the water is infected (1 to 5 percent), even if the infection of the tadpoles is already very high (50 to 100 percent). The parasite can therefore best be detected in the amphibian host, this is done by dissection and a subsequent microscopic search. The cysted metacercarias are usually located just below the skin, above the skeletal muscles.

distribution

The species has so far only been reliably proven from North America, where it is widespread. A related species lives in the Caribbean, Ribeiroia marini (Faust & Hoffmann, 1934). The very similar species could be distinguished by molecular genetics; its intermediate host is snails of the genus Biomphalaria . Another species has been described from the Congo (Africa). Recently another, previously undescribed species of the genus was discovered in Brazil. Malformations of amphibians by the other species of the genus are not known.

literature

  • Johnson, PTJ, DR Sutherland, JM Kinsella and KB Lunde (2004). Review of the trematode genus Ribeiroia (Psilostomidae): Ecology, life history and pathogenesis with special emphasis on the amphibian malformation problem. Advances in Parasitology 57: 191-253.

Individual evidence

  1. ↑ a b Joachim Czichos: Worm infection confirmed as a cause of malformations in amphibians. In: Image of Science. Konradin Medien GmbH, April 24, 2002, accessed on February 27, 2014 (the article refers to the English-language journal Ecological Monographs (vol. 72, p. 151)).
  2. ↑ Miranda D. Redmond, Richard B. Hartson, Jason T. Hoverman, Christina N. De Jesus-Villanueva, Pieter TJ Johnson (2011): Experimental Exposure of Helisoma trivolvis and Biomphalaria glabrata (Gastropoda) to Ribeiroia ondatrae (Trematoda). Journal of Parasitology, 97 (6): 1055-1061.
  3. ^ Johnson, Pieter; Lunde, Kevin; Haight, Ryan; Bowerman, Jay; Blaustein, Andrew: Ribeiroia ondatrae (Trematoda: Digenea) infection induces severe limb malformations in western toads (Bufo boreas) . In: Canadian Journal of Zoology . Issue 79 No. 3, 2001, p. 370–379 , doi : 10.1139 / z00-210 (English).
  4. ↑ Biodiversity protects amphibians from diseases caused by parasites - SPIEGEL ONLINE. In: Spiegel Online. SPIEGEL ONLINE GmbH, February 14, 2013, accessed on February 27, 2014 (the article refers to the English-language science magazine Nature (494, pp. 230–233, February 14, 2013)).
  5. ↑ Kevin B. Lunde & Pieter TJ Johnson (2012): A Practical Guide for the Study of Malformed Amphibians and Their Causes. Journal of Herpetology 46 (4): 429-441.
  6. ^ Wade D. Wilson, Pieter TJ Johnson, Daniel R. Sutherland, Helene Mone, Eric S. Loker (2005): A molecular phylogenetic study of the genus Ribeiroira (Digenea), trematodes known to cause limb malformations in amphibians. Journal of Parasitology 91 (5): 1040-1045.
  7. ^ HA Pinto, RC Jadin, SA Orlofske, PTJ Johnson, AL Melo (2013): Biomphalaria straminea (Mollusca: Planorbidae) as an intermediate host of Ribeiroia sp. (Trematoda: Psilostomidae) in Brazil. Journal of Parasitology 99 (5): 914-918.