Hematodinium is a genus of parasitic dinoflagellates that infects crustaceans worldwide including Tanner crabs Chionoecetes bairdi and snow crabs C. opilio in the Northeast Pacific Ocean. The present study describes the optimization of a PCR-based assay for the detection and monitoring of Hematodinium sp. in snow and Tanner crabs. Two fragments, 1682 and 187 bp, were amplified from the 18S ribosomal DNA region of the parasite. The assay performed well in 6 additional decapod species (1 lobster and 5 crabs) infected with Hematodinium spp., suggesting that it could be used to detect Hematodinium spp. in other decapods. We also report Hematodinium spp. infections in the majid crab, Hyas coarctatus, and the lithodid crab, Lithodes couesi. Sequencing of 18S rDNA and the adjacent internal transcribed spacer 1 (ITS1) region of Hematodinium spp. isolated from 7 host species in the present study revealed the presence of 2 Hematodinium clades, one in the blue crab Callinectes sapidus and a second in all other host species. The ITS1 sequences of the 2 clades could not be aligned, but showed a conserved secondary structure that may be related to a functional diversification during a host switch. Comparison of our data with 18S and ITS1 sequence data available in GenBank placed the north Pacific Hematodinium sp. in a clade separate from the Hematodinium sp. infecting the portunoids, C. sapidus, Liocarcinus depurator and Scylla serrata, and within a second clade that infected all other decapod hosts located in the North Pacific and North Atlantic Oceans.KEY WORDS: ITS1 · Secondary structure · 18S rDNA · Parasite · PCR · Crustacean · Parasitic · Dinoflagellate · Disease Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSDis Aquat Org 89: [155][156][157][158][159][160][161][162][163][164][165][166] 2010 including Portunus pelagicus, Norway lobsters Nephrops norvegicus and blue crabs Callinectes sapidus (reviewed in Stentiford & Shields 2005, Small et al. 2006, 2007b. Despite the potential economic and ecological impact of Hematodinium-related mortality on affected populations, little is known about the method of infection, the life history of the parasite outside the host and the underlying causes for the recent worldwide increase in frequency of Hematodiniumassociated disease.Traditional techniques of disease detection involve macroscopic examination of pleopods that generally result in detection of only relatively advanced infections (Stentiford et al. 2001) or microscopic examination of hemolymph smears. More sensitive, immunological methods for Hematodinium detection (Field & Appleton 1996, Stentiford et al. 2001, Small et al. 2002 are of insufficient specificity or may not recognize life stages of Hematodinium absent in the original inoculum or in alternate hosts (Bushek et al. 2002, Small et al. 2006. Use of the PCR has become increasingly widespread in pathogen identification and disease detection and monitoring and is particularly useful in the diagnosis of c...

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