Parvicapsula pseudobranchicola (Myxosporea) in farmed Atlantic salmon Salmo salar: tissue distribution, diagnosis and phylogeny

Diseases of Aquatic Organisms

E. Karlsbakk P. A. Sæther C. Koren T. Larsen B. D. NielsenA. E. Brøderud C. Høstlund K. R. FjellsøyK. Lervik L. Rosnes¹  A. Nylund¹ 

关键词: Parvicapsula pseudobranchicola;    P. unicornis;    P. asymmetrica;    ssu rDNA;    Molecular phylogeny;    Diagnostic PCR;   

DOI  :  10.3354/dao063197

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: Parvicapsula pseudobranchicola infections in farmed Atlantic salmon in Norway are associated with low-grade to significant mortalities. The parasite is found as mature spores in pseudobranchs, but has also been detected in the gills,liver and kidney. Diagnosis has relied on the detection of Parvicapsula spores, with the pseudobranch being the preferred organ. A better understanding of the epizootiology of this myxosporean is a prerequisite for appropriate management andcontrol. Hence, early detection of infections and life cycle studies are needed. We sequenced the small subunit (ssu) rDNA (18S) from P. pseudobranchicola and developed a sensitive diagnostic PCR protocol. This allowed us to (1) identifyappropriate tissues for diagnostic assays, (2) examine the intraspecific variation in ssu rDNA in the parasite’s Norwegian range, (3) examine annelid potential primary hosts and (4) obtain additional ssu rDNA sequences of marine Parvicapsulaspecies to perform a phylogenetic study. Primers were constructed targeting the ssu rDNA from P. minibicornis. With these we obtained a partial ssu sequence of the P. pseudobranchicola type isolate. A new set of primers (PCF3/PCR3) wasconstructed for diagnostic purposes. These were tested against DNA from the host and several myxozoan species infecting Norwegian salmon. The primers give a positive product of 203 bp and pick out P. pseudobranchicola in salmonids. They alsoamplify the congeners P. unicornis and P. asymmetrica infecting unrelated fish. The PCR protocol developed showed a greater sensitivity than light microscopy. The pseudobranchs were always positive and are the recommended organfor PCR diagnostics. There was no sequence variation between geographic isolates from farmed salmon. Preliminary examinations of marine polychaetes and oligochaetes collected from farm sites with parvicapsulose problems were negative. A comparison of thesequence of the ssu rDNA from P. pseudobranchicola with that of other myxozoans shows that it groups closely together with P. unicornis and P. asymmetrica. The closest relative to this group is P. minibicornis.

【 授权许可】

Unknown