Amphibians are the most threatened animal group on the planet. In 2008, 32 percent of frog species were classified as threatened or extinct, and 42 percent were listed as being in decline. The decline and extinctions have been attributed to newly emerging infectious diseases.
The newly documented parasitic disease is caused by single-celled microbes or protists. Protists are members of a large, diverse group of microorganisms, mainly unicellular (or single-celled), that do not form tissues. Protists live in any environment that contains liquid water.
To make the description of a protist clearer, think of algae as being a protist. Algae are photosynthetic and are vital primary producers in ecosystems such as the ocean. There are also pathogenic protists, like apicomplexan Plasmodium, which causes malaria.
Distant relative to an oyster disease called Dermo
The new disease was identified and described by scientists from the University of Exeter and the Natural History Museum in London. The disease was found in the livers of tadpoles from both tropical and temperate sites, and is a very distant relative of oyster parasites.
With the aid of phylogenetic analyses, it was revealed that the infectious agent was related to the Perkinsea: a parasitic group within the alveolates exemplified by Perkinsus marinus, a marine protist responsible for mass mortality events in oysters.
Source: E Burreson
Dr. Richards says, “Global frog populations are suffering serious declines and infectious disease has been shown to be a significant factor. We now need to figure out if this novel microbe causes significant disease and could be contributing to the frog population declines.”
What is of particular interest is a study conducted in 2014 on the diversity of Perkinsea-like phylotypes in freshwater and marine environments. In the study, researchers found only a few Perkinsea environmental sequences in the saltwater samples tested, whereas, in freshwater sampling, an abundance and diversity of Perkinsea-like phylotypes were found.
The 2014 study pointed out the considerable diversity of Perkinsea sp. and suggested “Perkinsea either play a significant but hitherto unrecognized role as parasites in marine sediments and/or members of this group are present in the marine sediment possibly as part of the ‘seed bank’ microbial community.”
The new study, which included ribosomal DNA sequencing, also revealed a wide variety of freshwater Perkinsea lineages in these environments. And it was interesting that the sampling of diseased tadpoles came from such diverse areas of the world, as well as including a wide taxonomic range of frogs, some from oceanic islands. Has the protist actually evolved in some way?
This interesting study, “Cryptic infection of a broad taxonomic and geographic diversity of tadpoles by Perkinsea protists,” was published on August 10, 2015, in the journal Proceedings of the National Academy of Sciences.
