Author(s): Marianna Vaz Rodrigues, Claire Juliana Francisco, Gianmarco Silva David, Reinaldo José da Silva and João Pessoa Araújo Júnior

Abstract: In November 2014 and March 2015, 360 O. niloticus were randomly sampled from six fish farms in Brazil and the organs were collected for histopathology, polymerase chain reaction, sequencing, and phylogeny tests. The histopathology revealed eosinophils, microsporidium, and inflammation in tissues of the majority of fish analyzed in this study. Microsporidia prevalence varied from 86.66% to 100%. Examination of wet mounts, revealed oval shaped micro-sporidian spores, their length ranging from 1.284 – 1.435 µm and their width 0.545 – 0.667 µm (n = 30). The nested PCR amplified a 407-bp product, which exhibited 97% sequence identity to Nucleospora salmonis. The phylogeny tests revealed that the microsporidia found in this study belonged to the Nucleospora genus. According to the clinical signs, histopathology findings, and molecular results, this study identifies an intranuclear microsporidium similar to Nucleospora infecting O. niloticus, which we named Nucleospora braziliensis sp. Nov.

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