title: Detection of the intranuclear microsporidium Nucleospora salmonis in naturally and experimentally exposed Chinook salmon Oncorhynchus tshawytscha by in situ hybridization.
abstract: Nucleospora salmonis, an intranuclear microsporidian parasite of salmonid fish, is often difficult to observe in histological sections or wet mount preparations from lightly infected tissues because of its small size and location within the nuclei of lymphoblast-type cells. Diagnosis of infections by conventional light microscopy is directly dependent upon distinguishing different stages of the parasite from host cell nuclear material or vacuoles. To assist detection of stages of the parasite in tissues of its primary host, the Chinook salmon (Oncorhynchus tshawytscha), we developed a nonradioactive in situ hybridization (ISH) method. The new method was then used to detect N. salmonis among Chinook salmon after both natural and experimental exposures to the parasite. Probes derived from the small subunit ribosomal DNA (ssu-rDNA) sequence of the microsporidium were labeled with digoxigenin deoxyuridine triphosphate (DIG-dUTP) and hybridized to parasite DNA present in infected tissues. The ISH procedure effectively identified merogonic and spore stages of N. salmonis in paraffin-embedded tissues of clinically and subclinically infected fish. A Nucleospora-like microsporidium was also detected by ISH in tissues of a nonsalmonid fish, the English sole (Pleuronectes vetulus), using probes designed to a region of the ssu-rDNA of N. salmonis.
authors.affiliation: Laboratoire de Biologie Cellulaire et Moléculaire des Parasites Opportunistes, URA CNRS 1944, Université Blaise Pascal, 63177, Aubière Cedex, France.
authors.forename: S J
authors.initials: SJ
authors.lastname: Grésoviac
authors.forename: D V
authors.initials: DV
authors.lastname: Baxa
authors.forename: C P
authors.initials: CP
authors.lastname: Vivarès
authors.forename: R P
authors.initials: RP
authors.lastname: Hedrick
mesh_terms: D000818:Animals; D003856:Deoxyuracil Nucleotides / Q000378:metabolism; D004076:Digoxigenin / Q000031:analogs & derivatives / Q000378:metabolism; D005393:Fish Diseases / Q000175:diagnosis* / Q000469:parasitology; D005432:Flounder / Q000469:parasitology; D017403:In Situ Hybridization / Q000379:methods*; D016814:Microsporidia / Q000235:genetics / Q000302:isolation & purification*; D016881:Microsporidiosis / Q000175:diagnosis / Q000662:veterinary*; D015345:Oligonucleotide Probes / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012474:Salmon / Q000469:parasitology*; D013194:Staining and Labeling
chemical_list: D003856:Deoxyuracil Nucleotides; D015345:Oligonucleotide Probes; D012337:RNA, Ribosomal, 18S; C070202:digoxigenin-11-deoxyuridine triphosphate; D004076:Digoxigenin