A polycystic kidney disease in hyperolid frogs (Hyperolius sp. ) from Tanzania due to infection with a species of Hoferellus (Berg, 1898) (Myxozoa)

Frank Mutschmann

Exomed, Am Tierpark 64, 10319 Berlin/Germany
Email: mutschmann@aol.com

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. Due to their spore characteristics, the parasites belongs to the genus Hoferellus Berg, 1898. The spores are pyramidal (length: 7 - 9 mm; wide: 6 - 7 mm) with two polar capsules (3 - 4 x 2 mm) on the apical ends of the spores. The surface of the spores is longitudinally striated.

The genus Hoferellus was previously found only in cyprinid fish from Europe and Asia (including Japan). This is the first record of a Hoferellus in amphibians generally and in vertebrates from the African continent (species description is in progress). The parasites were also found in the urinary bladder (plasmodia, spores) as well as in the epithelium (developmental stages) and lumen (free spores) of the gut. The pathological changes were mainly found in kidneys. In histological sections, the kidneys displayed a massive granulocytosis as well as edema and necrosis of epithelial renal tubuli cells. Parasitic stages were detected inside the tubuli cells. The pathological findings are similar to the well known situation in Hoferellus-infected cyprinid fish, the so called "kidney enlargement disease (KED) - an important factor in commercial fish production . In goldfish (Carassius auratus) the life cycle of the parasite (H. carassi) includes an actinosporid stage (Aurantiactinomyxon) in invertebrates (Oligochaetes) of the genus Nais (Trouillier et al. 1996). The oral route of infection by feeding on oligochaetes may also be possible in anurans (larval stages).