There’s a new parasite infecting tadpoles, filling their livers with thousands of foreign cells. And they are found all over the world in both tropical and temperate regions alike. 

Frogs and salamanders are among the most threatened animal groups on the planet right now, with 42% of all amphibian species declining in population. And with these declines come emerging infectious diseases. An amphibian mass mortality event in the U.S. in 2006 has been linked to a pathogen that’s closely related to a shellfish parasite called Perkinsus. Infected tadpoles of the southern leopard frog (Lithobates sphenocephalus) have an abnormally enlarged, yellowish liver filled with thousands of spherical cells, likely from the parasitic Perkinsea family of microorganisms called protists. So far, three Perkinsus species have been described parasitizing marine bivalves, plankton, and algae. 

Using molecular methods, an international team led by University of Exeter’s Aurélie Chambouvet and Thomas Richards wanted to evaluate the prevalence and diversity of Perkinsea-like parasites infecting tadpoles across the planet. Using a particular kind of sequencing known as small subunit ribosomal DNA sequencing, they were able to develop a targeted protocol that screens for Perkinsea. To test their protocol, they sampled freshwater environmental DNA from U.K. and French Guiana water masses and found a wide diversity of Perkinsea lineages.    

Then they used the same protocol to test for Perkinsea-like lineages in the livers of 182 tadpoles from multiple families of frogs living in six countries: U.K., French Guiana, Tanzania, Cameroon, the island of São Tomé, and the Czech Republic. They found previously unidentified Perkinsea-like parasites in 38 tadpoles sampled from five of those countries (all but the Czech Republic). These span three continents and include both tropical and temperate regions, as well as an oceanic island. 

The newly discovered parasites are different from the Perkinsea-like pathogen responsible for the 2006 amphibian mass mortality event in Georgia – which suggests that multiple Perkinsea lineages are infecting tadpoles. 

These findings, published in Proceedings of the Academy of Sciences this week, are the first evidence that Perkinsea-like protists are infecting a wide diversity of tadpoles occupying a variety of geographic ranges.