Myxobolus lentisuturalis infection in a farmed population of goldfish Carassius auratus from the USA.

Myxobolus lentisuturalis is a myxozoan parasite of piscine muscle that has been described in goldfish Carassius auratus and Prussian carp Carassius gibelio. This report documents a naturally occurring infection of M. lentisuturalis in a population of farmed goldfish in the USA. Postmortem examination was performed on 4 affected goldfish. Gross findings included large cystic cavities along the dorsal midline filled with caseous exudate. Histopathology revealed myxozoan plasmodia and spores in the epaxial muscles with varying degrees of granulomatous and necrotizing myositis accompanied by lymphohistiocytic meningoencephalitis. Spore morphology and dimensions were consistent with M. lentisuturalis, as observed by light microscopy. PCR and sequence analysis of the small subunit ribosomal DNA of infected muscle samples from 2 goldfish confirmed the parasite to have 99-100% nucleotide identity to M. lentisuturalis sequences recovered from similar cases of this parasite infecting goldfish in China and Italy and Prussian carp in China. This is the first reported case of M. lentisuturalis in the USA and furthers the understanding of the pathogenicity of this under-described parasite.