Abstract for "Getting the Jump on Amphibian Disease"

This article on "Getting the Jump on Amphibian Disease" talks about one documented cause of polycystic kidney disease, in a frog, at least:

"A number of hyperolid frogs were captured in the wild in Tanzania and imported to Germany for scientific reasons in December 1999. The species is as yet unidentified. The frogs were imported as Hyperolius marmoratus but this species does´not seem common in Tanzania. 5 adult frogs (3 males and 2 females) died in air transport and were dissected routinely. 3 specimens showed signs of ascites. In these animals (2 males, 1 female), a polycystic change of the kidneys was discovered by macroscopic examination. The kidneys appeared swollen and contained numerous cyst-like processes (up to 1 mm in diameter) on the surface. These cysts were filled with pale yellowish fluids containing red blood cells, granulocytes and masses of free spores, plasmodia and other developmental stages of a myxozoon parasite."

From the way PKD is described, a parasite theory would seem to fit. Like, starts with a few cysts, they replicate and shut down the organ they're living on, eventually (potentially) "travelling" to other organs.