Research Highlights: Frogs can grow more legs if infected with a parasite

Image credit: Pieter Johnson, courtesy of Oregon State University

Frogs can grow more legs if infected with a parasite

  • Do you know that a frog can have more legs if infected with a parasite?
  • Parasites can change the structure of their host.
  • For example, some trematodes can cause limb malformations in amphibians.
  • Researchers examined the relationship between morphological abnormalities in amphibians and the abundance of trematode parasites infection.
  • The research covered parts of California, Idaho, Washington, Oregon, and Montana.
  • Researchers studied malformations at frequencies ranging between 1 to 90 percent in nine amphibian species.
  • Researchers discovered that Ribeiroia ondatrae was linked to higher occurrence of amphibian limb malformations.
  • The parasite can be found mostly around the basal tissue of the hind limbs in infected frogs.
  • The malformations included skin webbings, more limbs and digits, and missing/malformed hind limbs.
  • Amphibians without the parasite showed significantly less occurrence of abnormalities.
  • The species that exhibited the highest abnormality frequencies include Ambystoma macrodactylum, Hyla regilla, Rana aurora, R. luteiventris, and Taricha torosa.
  • Water quality did not show significant relationship with the malformations.
  • The snail Planorbella were significant predictors of the presence of Ribeiroia infection.
  • The discovery demonstrated that Ribeiroia infection is the cause of amphibian malformations of the limbs in the western United States.


Johnson, Pieter & Lunde, Kevin & Thurman, Earl & Ritchie, Euan & Wray, Simon & Sutherland, Daniel & Kapfer, Joshua & Frest, Terrence & Bowerman, Jay & Blaustein, Andrew. (2002). Parasite (Ribeiroia ondatrae) Infection Linked to Amphibian Malformations in the Western United States. Ecological Monographs. 72. 151-168. 10.2307/3100022.

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