Mortality event in freshwater drum Aplodinotus grunniens from Lake Ontario, Canada, associated with viral haemorrhagic septicemia virus, type IV

Comparison of quantitative RT-PCR with cell culture to detect viral hemorrhagic septicemia virus (VHSV) IVb infections in the Great Lakes

Viral hemorrhagic septicemia virus (VHSV) is an important pathogen of cultured and wild fish in marine and freshwater environments. A new genotype, VHSV IVb, was isolated from a fish collected from the Great Lakes in 2003. Since the first isolation, VHSV IVb has been confirmed in 28 species, signaling the early invasion and continued spread of this Office International des Epizooties-reportable agent. For surveillance of this virus in both wild and experimental settings, we have developed a rapid and sensitive one-step quantitative real-time polymerase chain reaction (qRT-PCR) assay that amplifies a 100-base-pair conserved segment from both the genomic negative strand and the mRNA positive strand of the nucleoprotein (N) gene of VHSV IVb. This assay is linear over seven orders of magnitude, with an analytical capability of detecting a single copy of viral RNA and reproducibility at 100 copies. The assay is approximately linear with RNA input from 50 to 1000 ng per assay and works equally well with RNA prepared from a column-based or phenol-chloroform-based method. In wild-caught fish, 97% of the cases were found to be more than three orders of magnitude more sensitive using qRT-PCR than using cell culture. Of the 1,428 fish from the Great Lakes region tested in 2006 and 2007, 24% were positive by qRT-PCR whereas only 5% were positive by cell culture. All of the fish that were positive by cell culture were also positive by qRT-PCR. Importantly, qRT-PCR sensitivity is comparable to that of cell culture detection when comparing VHSV viral RNA levels with viral titer stocks, confirming that the high qRT-PCR signals obtained with diagnostic samples are due to the accumulation of N gene mRNA by transcriptional attenuation. The qRT-PCR assay is particularly valuable for rapid and high-throughput prescreening of fish before confirmatory testing by cell culture or sequencing tissue-derived amplicons and especially in detecting infection in fish that do not show clinical signs of VHS.

The source of self: genetic parasites and the origin of adaptive immunity

Stable colonization of the host by viruses (genetic parasites) can alter the systems of host identity and provide immunity against related viruses. To attain the needed stability, some viruses of prokaryotes (P1 phage) use a strategy called an addiction module. The linked protective and destructive gene functions of an addiction module insures both virus persistence but will also destroy cells that interrupt this module and thereby prevent infection by competitors. Previously, I have generalized this concept to also include persistent and lytic states of virus infection, which can be considered as a virus addiction module. Such states often involve defective viruses. In this report, I examine the origin of the adaptive immune system from the perspective of a virus addiction module. The likely role of both endogenous and exogenous retroviruses, DNA viruses, and their defective elements is considered in the origin of all the basal components of adaptive immunity (T-cell receptor, RAG-mediated gene rearrangement, clonal lymphocyte proliferation, antigen surface presentation, apoptosis, and education of immune cells). It is concluded that colonization by viruses and their defectives provides a more coherent explanation for the origin of adaptive immunity.

Detection of Viral Hemorrhagic Septicemia virus (VHSV) from the leech Myzobdella lugubris Leidy, 1851

The leech Myzobdella lugubris is widespread in the Lake Erie Watershed, especially Lake St. Clair. However, its role in pathogen transmission is not fully understood. In this same watershed, several widespread fish mortalities associated with the Viral Hemorrhagic Septicemia virus (VHSV) were recorded. Viral Hemorrhagic Septicemia is an emerging disease in the Great Lakes Basin that is deadly to the fish population, yet little is known about its mode of transmission. To assess the potential role of M. lugubris in VHSV transmission, leeches were collected from Lake St. Clair and Lake Erie and pooled into samples of five. Cell culture and reverse transcriptase polymerase chain reaction (RT-PCR) were used to determine the presence of the virus and its identity. Results showed that 57 of the 91 pooled leech samples were positive by cell culture for VHSV and 66 of the 91 pooled leech samples were positive by RT-PCR for the VHSV. Two representative virus isolates were sequenced for further genetic confirmation and genotype classification. VHSV detected within M. lugubris was homologous to the Great Lakes strain of VHSV genotype IVb. This is the first record of the VHSV being detected from within a leech, specifically M. lugubris, and suggests the potential of M. lugubris being involved in VHSV transmission.

Fish cardiovascular physiology and disease

Fish patients with cardiovascular disorders present a challenge in terms of diagnostic evaluation and therapeutic options. Veterinarians can approach these cases in fish using methods similar to those employed for other companion animals. Clinicians who evaluate and treat fish in private, aquarium, zoologic, or aquaculture settings need to rely on sound clinical judgment after thorough historical and physical evaluation. Pharmacokinetic data and treatments specific to cardiovascular disease in fish are limited; thus, drug types and dosages used in fish are largely empiric. Fish cardiovascular anatomy, physiology, diagnostic evaluation, monitoring, common diseases, cardiac pathologic conditions, formulary options, and comprehensive references are presented with the goal of providing fish veterinarians with clinically relevant tools.

The first report of viral haemorrhagic septicaemia in farmed rainbow trout, Oncorhynchus mykiss (Walbaum), in the United Kingdom

Viral haemorrhagic septicaemia (VHS) was diagnosed in rainbow trout in the UK in May 2006. VHS virus (VHSV) was isolated from fingerlings showing typical histopathological lesions at a single rainbow trout farm site experiencing high mortality. The virus was confirmed as VHSV by serological and molecular biological tests. Phylogenetic analysis based on the complete glycoprotein gene sequence revealed that the isolate was closely related (99% nucleotide identity) to several Danish isolates from 1991 to 2000 and was assigned to VHSV genogroup Ia. The pathogenicity of the isolate was determined in infection experiments using rainbow trout fry. Following waterborne challenge, cumulative mortalities reached 96.67-100% by 12 days post-infection. This represents the first isolation of a pathogenic freshwater VHSV in the UK.