DAO 126:185-198 (2017)  -  DOI: https://doi.org/10.3354/dao03170

ABSTRACT: We used microscopy and molecular biology to provide the first documentation of infections of Myxobolus cerebralis (Myxozoa: Myxobolidae), the etiological agent of whirling disease, in trout (Salmonidae) from North Carolina (USA) river basins. A total of 1085 rainbow trout Oncorhynchus mykiss, 696 brown trout Salmo trutta, and 319 brook trout Salvelinus fontinalis from 43 localities across 9 river basins were screened. Myxospores were observed microscopically in pepsin-trypsin digested heads of rainbow and brown trout from the Watauga River Basin. Those infections were confirmed using the prescribed nested polymerase chain reaction (PCR; 18S rDNA), which also detected infections in rainbow, brown, and brook trout from the French Broad River Basin and the Yadkin Pee-Dee River Basin. Myxospores were 9.0–10.0 µm (mean ± SD = 9.6 ± 0.4; N = 119) long, 8.0–10.0 µm (8.8 ± 0.6; 104) wide, and 6.0–7.5 µm (6.9 ± 0.5; 15) thick and had polar capsules 4.0–6.0 µm (5.0 ± 0.5; 104) long, 2.5–3.5 µm (3.1 ± 0.3; 104) wide, and with 5 or 6 polar filament coils. Myxospores from these hosts and rivers were morphologically indistinguishable and molecularly identical, indicating conspecificity, and the resulting 18S rDNA and ITS-1 sequences derived from these myxospores were 99.5–100% and 99.3–99.8% similar, respectively, to published GenBank sequences ascribed to M. cerebralis. This report comprises the first taxonomic circumscription and molecular confirmation of M. cerebralis in the southeastern USA south of Virginia.

KEY WORDS: Trout · Salmonid · Southeastern USA · Whirling disease · Morphology · Molecular diagnostics