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The article discusses a study that highlights the genetic diversity of Viral hemorrhagic septicemia virus (VHSV) in North America's Great Lakes region. Based on the phylogenetic analysis, the study discovered that it is into the sub-lineage IVb within the major VHSV genetic group IV that all isolates fell. The study found that vcG001 and vcG002 were the two dominant sequence types, which makes 90% of the isolates. It concluded that the genetic diversity of VHSV in the Great Lakes region was extremely low due to the introduction of new virus in the region.

The article discusses research on the formation of a continuous fibroblastic-like cell line (BEF-1), which was derived from two late stage embryos of a North American burbot called Lota Lota maculosa, and its level of susceptibility to several viruses of fish. It notes the limited effectiveness of aminoglycosides neomycin, streptomycin and beta-lactum penicillin as antimycotics, and that such drugs seemed not to create adverse impacts on BEF-1 cell culture. The research revealed a lower level of susceptibility to several isolates of infectious hematopoietic necrosis virus (IHNV) and viral hemorrhagic septicemia virus (VHSV), compared with other developed cell lines. The authors state that use of such cell line is not appropriate for diagnosis of IPNV.

Four viral hemorrhagic septicemia virus (VHSV) genotype IVb isolates were sequenced, their genetic variation explored, and comparative virulence assayed with experimental infections of northern pike Esox lucius fry. In addition to the type strain MI03, the complete 11183 bp genome of the first round goby Neogobius melanostomus isolate from the St. Lawrence River, and the 2013 and 2014 isolates from gizzard shad Dorosoma cepedianum die-offs in Irondequoit Bay, Lake Ontario and Dunkirk Harbor, Lake Erie were all deep sequenced on an Illumina platform. Mutations documented in the 11 yr since the MI03 index case from Lake St. Clair muskellunge Esox masquinongy showed 87 polymorphisms among the 4 isolates. Twenty-six mutations were non-synonymous and located at 18 different positions within the matrix protein, glycoprotein, non-virion protein, and RNA polymerase genes. The same 4 isolates were used to infect northern pike fry by a single 1 h bath exposure. Cumulative percent mortality varied from 42.5 to 62.5%. VHSV was detected in 57% (41/72) of the survivors at the end of the 21-d trial, suggesting that the virus was not rapidly cleared. Lesions were observed in many of the moribund and dead northern pike, such as hemorrhaging in the skin and fins, as well as hydrocephalus. Mean viral load measured from the trunk and visceral tissues of MI03-infected pike was significantly higher than the quantities detected in fish infected with the most recent isolates of genotype IVb, but there were no differences in cumulative mortality observed.

Infectious hematopoietic necrosis virus (IHNV) is an acute pathogen of salmonid fishes in North America, Europe and Asia and is reportable to the World Organization for Animal Health (OIE). Phylogenetic analysis has identified 5 major virus genogroups of IHNV worldwide, designated U, M, L, E and J; multiple subtypes also exist within those genogroups. Here, we report the development and validation of a universal IHNV reverse-transcriptase real-time PCR (RT-rPCR) assay targeting the IHNV nucleocapsid (N) gene. Properties of diagnostic sensitivity (DSe) and specificity (DSp) were defined using laboratory-challenged steelhead trout Oncorhynchus mykiss, and the new assay was compared to the OIE-accepted conventional PCR test and virus isolation in cell culture. The IHNV N gene RT-rPCR had 100% DSp and DSe and a higher estimated diagnostic odds ratio (DOR) than virus culture or conventional PCR. The RT-rPCR assay was highly repeatable within a laboratory and highly reproducible between laboratories. Field testing of the assay was conducted on a random sample of juvenile steelhead collected from a hatchery raceway experiencing an IHN epizootic. The RT-rPCR detected a greater number of positive samples than cell culture and there was 40% agreement between the 2 tests. Overall, the RT-rPCR assay was highly sensitive, specific, repeatable and reproducible and is suitable for use in a diagnostic setting.

To improve our understanding of the genetic basis of fish disease, we developed a pathogen model, using zebrafish (Danio rerio) and spring virema of carp virus (SVCV). Replicate groups of 10 fish were acclimated to 20 or 24 degrees C, then were exposed to SVCV concentrations of 10(3) to 10(5) plaque-forming units per milliliter (PFU/ml) of water and observed daily. In a second trial, fish were acclimated to 15 degrees C, and replicate groups of 10 fish were exposed to SVCV at a concentration of 10(5) PFU/ml; however, the temperature was raised 1 degrees C/wk. Moribund fish were collected for histologic examination, and dead fish were assayed for virus by use of cell culture and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Mortality exceeded 50% in fish exposed to 10(5) PFU of SVCV/ml at the lower temperatures. Clinical signs of disease became evident seven days after viral exposure and were observed most consistently in fish of the 10(5) PFU/ml groups. Affected zebrafish were anorectic and listless, with epidermal petechial hemorrhages followed by death. Use of plaque assays and RT-PCR analysis confirmed presence of SVCV at titers > or = 10(4) PFU/g of tissue. Histologic lesions included multifocal brachial necrosis and melanomacrophage proliferation in gills, liver, and kidneys. These results indicate that zebrafish are susceptible to infection by SVCV under conditions that mimic a natural route of exposure.