Milky hemolymph syndrome (MHS) associated with a virus in tanner crab Chionoecetes bairdi off the Pacific coast of Kamchatka.

Milky hemolymph syndrome (MHS) caused by a bacilliform virus (BV) was found in tanner crab Chionoecetes bairdi in the shelf zone of Kamchatka. The prevalence of the disease varied from 0.18 to 1.02%. A total lesion of the cells of the interstitial connective tissue and the connective tissue component of all internal organs was noted, which was expressed in the hypertrophy of their nuclei. In addition, hypertrophy of fixed phagocytes and circulating hemocytes was noted. Ultrastructural analysis of the tissues confirmed that in the interstitial connective tissue of pathologically altered organs, virus particles of two morphotypes were found - rod-shaped and globular. In the cytoplasm of infected cells, bands of microtubules formed near where viral particles were concentrated. In the area of contacts at the poles of microtubules, successive stages of the transformation of rod-shaped viruses into globular viruses was observed. The bacilliform virus that infects C. bairdi is structurally very similar to CoBV found in Chionoecetes opilio. Structural features are characteristic of representatives of fam. Nimaviridae. The molecular data obtained suggest that the virus causing MHS in C. bairdi is systematically very close, if not identical, to CoBV.

First detection of Hematodinium sp. In spiny king crab Paralithodes brevipes, and new geographic areas for the parasite in tanner crab Chionoecetes bairdi, and red king crab Paralithodes camtschaticus.

A parasitic dinoflagellate of the genus Hematodinium was found off the Pacific coast of Kamchatka in three species of crabs: red king crab Paralithodes camtschaticus, tanner crab Chionoecetes bairdi, and spiny king crab Paralithodes brevipes. This is the first detection of Hematodinium in spiny king crab. The results of the genetic analysis showed that the pathogen found in P. brevipes, P. camtschaticus, and C bairdi from the Avacha and Kronotsky bays off the Pacific coast of Kamchatka was the same or very close to the Hematodinium sp., which infects many species of crustaceans in the Northern Hemisphere. The prevalence of infection was 0.2% for tanner crabs and 2.7% for red king crabs. Due to a limited sample size, we were unable to calculate the prevalence for spiny king crabs and female red king crabs. Both the macroscopic and microscopic signs of the pathology were similar in all diseased crabs. The differences in the micromorphology of the Hematodinium cells we found in the three crab species, including the presence or absence of trichocysts, the shape of the plasmodia, and the structure of pore complexes, are most likely related to the life cycle and the physiology of the parasite. The results of the genetic analysis showed that the pathogen found in P. brevipes, P. camtschaticus, and C. bairdi from the Avacha and Kronotsky bays of the Pacific coast of Kamchatka was the same or very close to the Hematodinium sp., which infects many species of crustaceans in the Northern Hemisphere.

First report of bacterial kidney disease in coho salmon Oncorhynchus kisutch in Russia.

This paper describes the first case of bacterial kidney disease (BKD) to be identified in coho salmon Oncorhynchus kisutch in Russia. The fish in question was caught in Lake Bolshoi Vilyui on the Kamchatka Peninsula. The diseased fish had foci of granulomatous inflammation in the kidneys. The diagnosis was confirmed by isolating the bacterium Renibacterium salmoninarum from kidney tissue in pure culture, and by determining the partial 16S RNA gene sequence of the isolate. This is the first detection of this pathogen in the genus Oncorhynchus in Russia, and detection of BKD in coho salmon indicates that the pathogen is present in the natural fish populations of Kamchatka. Therefore, it will be necessary to conduct screening studies of mature salmon selected for artificial reproduction, for the presence of BKD signs and asymptomatic infection with R. salmoninarum, which will allow us to estimate the prevalence of the pathogen.

First record of new rickettsia-like organism in the blue king crab Paralithodes platypus from the Sea of Okhotsk: Distribution, morphological evidence and genetic analysis.

An infection caused by a rickettsia-like organism (RLO) was detected in the blue king crab Paralithodes platypus from the eastern Sea of Okhotsk. The external signs of the disease are lethargy and an empty gastrointestinal tract. Dissection of infected individuals revealed that their hepatopancreas was light yellow in color. The causative agent of infection is Gram-negative rod-shaped bacterium targeted exclusively at hepatopancreas tissues. In the cytoplasm of infected cells, the bacteria are enclosed in parasite vacuoles or located immediately in cytosol. An ultrastructural analysis showed two main morphological types corresponding to the life cycle stages in the RLO: the vegetative stage of intermediate bodies, characterized by growth and division processes, and the infection stage of elementary bodies, which are spore-like non-dividing short rods surrounded by a multilayered membrane and having an osmiophilic inclusion body. At the terminal stage of infection, as a result of lysis of the infected cells, the RLO enters the lumen of the hepatopancreatic tubules which contributes to the spread of infection. According to genetic analysis based on 16S rRNA gene sequences, the RLO from P. platypus is most closely related to the Candidatus Hepatobacter penaei, NCBI #JX981946 (94.7% similarity) and NCBI #KY363553 (94.1% similarity). The high level of genetic differences (more than 5%) of the studied pathogen, along with the structural features, allows characterizing the RLO isolated from P. platypus as a new species of the genus Candidatus Hepatobacter paralithodi nov. sp., NCBI #MK928971.

A new host for Hematodinium infection among lithodid crabs from the Sea of Okhotsk.

A disease caused by parasitic dinoflagellates of the genus Hematodinium has been found in the soft crab Hapalogaster grebnitzkii from the Sea of Okhotsk, which is considered a new host for this agent among lithodid crabs. This report provides macro- and micromorphological descriptions (using light and transmission electron microscopy) of the disease, as well as molecular identification of Hematodinium sp. from soft crabs, based on 18S RNA sequence data.

A herpes-like virus in king crabs: Characterization and transmission under laboratory conditions.

A herpes-like virus was found infecting the antennal gland and bladder epithelium in the blue king crab Paralithodes platypus from the eastern area of the Sea of Okhotsk. Electron microscopic analysis of antennal gland samples from blue king crabs with histologically confirmed signs of disease revealed virus particles, which were mostly hexagonal in shape and located primarily in the nucleus; these particles were rarely observed in the cytoplasm of infected cells. Most virus particles ranged in size from 115 to 125nm. Hemocytes of the red king crab Paralithodes camtschaticus in cell culture could be experimentally infected with virus from thawed antennal gland samples of the blue king crabs with histologically confirmed signs of viral infection. Clear signs of infection were observed in hemocyte cultures at 3-4days post-inoculation as small foci of highly vacuolated formations. These formations included several nuclei and were surrounded by a halo of small cytoplasmic bubbles containing actin and tubulin. As demonstrated by electron microscopic studies, no virus-like particles were found in the cells 1day post-inoculation, but particles become abundant at 7days post-inoculation. We developed a consensus primer PCR method for amplification of a region of the herpesviral DNA-directed DNA polymerase. Primers were designed to target sequences encoding highly conserved amino acid motifs covering a region of approximately 800bp. Thus, macroscopic, histological and ultra-structural examinations of blue king crabs infected with a virus and the molecular identification of the pathogen revealed the presence of herpesviruses. The frequency of the herpes-like viral infection in natural populations of blue king crabs in the Sea of Okhotsk ranged from 0% to 3% in different years.

Hematodinium sp. infection of red Paralithodes camtschaticus and blue Paralithodes platypus king crabs from the Sea of Okhotsk, Russia.

A disease caused by a parasitic dinoflagellate of the genus Hematodinium was identified in red, Paralithodes camtschaticus, and blue, Paralithodes platypus, king crabs from the north-east region of the Sea of Okhotsk, Russia, during annual stock surveys. No carapace color change was observed even in heavily infected crabs, but diseased crabs possessed creamy-yellow hemolymph, which was visible through the arthrodial membranes of the abdomen and appendages. Several stages of the parasite's life history, including trophonts, plasmodia, sporonts and macrodinospores, were observed in tissues of infected king crabs. Numerous parasite cells were observed in the lumina of the myocardium, the gills, the connective tissue of antennal glands and the sinuses of nerve ganglia, eyestalks and gastrointestinal tract of king crabs with gross signs of infection. Based on sequencing of the 18S rDNA, it appears that the Hematodinium sp. found in red and blue king crabs is identical or closely related to Hematodinium sp. isolated from crabs of the genera Chionoecetes and Lithodes. Observed prevalences were 0.33% in sublegal male red king crabs, 0.18% in female red king crabs, 0.34% in sublegal male blue king crabs and 0.31% in female blue king crabs.