A previously little-known infectious disease has emerged as a major killer of frogs in Minnesota and nine other states, according to a study by the U.S. Geological Survey recently published the journal Nature.

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Scientists studied 247 frog die-offs in 43 states from 1999 through 2015 and found that severe Perkinsea infections, or SPI, caused 21 major mortality events in 10 states total.

Those included mass die-offs at locations in Minnesota, Florida, Georgia, Mississippi and New Hampshire where in some cases up to 95 percent of the tadpoles died from the disease.

Already hard hit by loss of habitat, chemical pollution and other problems, amphibians such as frogs and salamanders also are highly susceptible to diseases, the USGS said Tuesday. They are among the most endangered groups of animals on the planet, the USGS said.

"SPI fulfills several criteria consistent with a disease capable of causing local population declines and extinctions," the study noted.

SPI is caused by a tiny, one-celled parasitic organism called a protist.

The two most common frog diseases, chytridiomycosis and ranavirus infection, already had been linked to frog population declines worldwide. Now, the new study suggests that SPI is the third most common infectious disease among frogs.

"Amphibians such as frogs are valuable because they serve as pest control by eating insects like mosquitos, and they are food for larger predators," said Marcos Isidoro Ayza, a USGS scientist, University of Wisconsin-Madison fellow and the lead author of the study. "They're also exceptional indicators of ecosystem health. Like the proverbial canary in a coal mine, amphibians let us know when something in our environment is going awry."

The study found the disease in 11 different frog species.

"SPI in frogs may be underdiagnosed because it is not a disease for which they are typically screened," Isidoro Ayza said. "Incorporating routine screening of critical habitats for infected frogs is crucial to help understand the distribution of this destructive disease."

The disease kills tadpoles by causing multi-organ failure, and there is no cure or treatment for SPI at this time. SPI is not known to affect humans or pets. Affected tadpoles exhibited gross and histopathologic lesions in the liver, mesonephros, spleen, pancreas, gills, gastrointestinal tract, skeletal muscle, dermis and peritoneum.