Redefining piscine lactococcosis.

Unlabelled: Piscine lactococcosis is a significant threat to cultured and wild fish populations worldwide. The disease typically presents as a per-acute to acute hemorrhagic septicemia causing high morbidity and mortality, recalcitrant to antimicrobial treatment or management interventions. Historically, the disease was attributed to the gram-positive pathogen .

Temperature-associated virulence, species susceptibility and interspecies transmission of a Lactococcus petauri strain from rainbow trout.

Lactococcus petauri is an important emergent aquaculture pathogen in the USA. To better understand environmental conditions conducive to piscine lactococcosis and the susceptibility of fish species, laboratory-controlled challenges were used as models of infection. Rainbow trout Oncorhynchus mykiss maintained at 13 or 18°C were challenged by intracoelomic (ICe) injection with 101, 103 or 105 colony-forming units per fish (CFU fish-1) and monitored for 21 d.

Comparative Evaluation of Booster Vaccine Efficacy by Intracoelomic Injection and Immersion with a Whole-Cell Killed Vaccine against Infection in Rainbow Trout ().

is an important emergent bacterial pathogen of salmonids in the USA. The purpose of this study was to evaluate the protection conferred to rainbow trout () against by formalin-killed vaccines in immersion and injectable forms, as well as the enhanced protection afforded by booster vaccination. In the first challenge, fish were immunized via intracoelomic injection (IC) or immersion (Imm) routes alone.

Development of a quantitative polymerase chain reaction assay for detection of the aetiological agents of piscine lactococcosis.

Piscine lactococcosis is an emergent bacterial disease that is associated with high economic losses in many farmed and wild aquatic species worldwide. Early and accurate detection of the causative agent of piscine lactococcosis is essential for management of the disease in fish farms. In this study, a TaqMan quantitative polymerase chain reaction (qPCR) targeting the 16S-23S rRNA internal transcribed spacer region was developed and validated.

Isolation and characterization of Lactococcus garvieae from rainbow trout, Onchorhyncus mykiss, from California, USA.

Lactococcus garvieae is an emergent bacterial pathogen of salmonid fish in North America that causes acute infections particularly at water temperatures above 15°C. During 2020, L. garvieae was detected in rainbow trout, Onchorhyncus mykiss, cultured in Southern California and the Eastern Sierras.

First Isolation of a Novel Aquatic Flavivirus from Chinook Salmon (Oncorhynchus tshawytscha) and Its Replication in a Piscine Animal Model.

The first isolation of a flavivirus from fish was made from moribund Chinook salmon () from the Eel River, California, USA. Following the observation of cytopathic effect in a striped-snakehead fish cell line, 35-nm virions with flaviviral morphology were visualized using electron microcopy. Next-generation sequencing and rapid amplification of cDNA ends obtained the complete genome.

Invasion and initial replication of ultraviolet irradiated waterborne infective stages of Myxobolus cerebralis results in immunity to whirling disease in rainbow trout.

Myxobolus cerebralis is a microscopic metazoan parasite (Phylum Myxozoa: Myxosporea) associated with salmonid whirling disease. There are currently no vaccines to minimise the serious negative economical and ecological impacts of whirling disease among populations of salmonid fish worldwide. UV irradiation has been shown to effectively inactivate the waterborne infective stages or triactinomyxons of M.

Persistence of Piscirickettsia salmonis and detection of serum antibodies to the bacterium in white seabass Atractoscion nobilis following experimental exposure.

White seabass Atractoscion nobilis surviving experimental exposure to Piscirickettsia salmonis harbored the bacterium for periods up to at least 123 d post injection (dpi). Intraperitoneal injections of juvenile white seabass with 1.26 x 10(2) TCID50 P.

Evaluation of quantitative real-time PCR for rapid assessments of the exposure of sentinel fish to Myxobolus cerebralis.

Pathogen-free rainbow trout (Oncorhynchus mykiss) aged 735 degree days were experimentally exposed to a low dose of infectious Myxobolus cerebralis (20 triactinomyxons fish(-1)). Three time periods were chosen for sampling that included 10 days (d), 67 d, and 5 months (mo) post exposure. Five diagnostic assays were used: (1) conventional single-round polymerase chain reaction (PCR), (2) nested PCR, (3) real-time TaqMan PCR, (4) pepsin-trypsin digest, and (5) histopathology.

Identification of a serine protease gene expressed by Myxobolus cerebralis during development in rainbow trout Oncorhynchus mykiss.

Serine proteases have been recognized as key factors in parasite physiology and disease development. We have identified a serine protease gene from Myxobolus cerebralis, MyxSP-1, the myxozoan parasite causing whirling disease in salmonid fishes. The amino acid sequence, as deduced from the cDNA sequence, included a catalytic residue arrangement similar to that of the chymotrypsin family of serine proteases.

Evaluation of five diagnostic methods for the detection and quantification of Myxobolus cerebralis.

Diagnostic methods were used to identify and quantify Myxobolus cerebralis, a myxozoan parasite of salmonid fish. In this study, 7-week-old, pathogen-free rainbow trout (Oncorhynchus mykiss) were experimentally infected with M. cerebralis and at 7 months postinfection were evaluated with 5 diagnostic assays: 1) pepsin-trypsin digest (PTD) to detect and enumerate spores found in cranial cartilage, 2) 2 different histopathology grading scales that provide a numerical score for severity of microscopic lesions in the head, 3) a conventional single-round polymerase chain reaction (PCR), 4) a nested PCR assay, and 5) a newly developed quantitative real-time TaqMan PCR.

Myxobolus cerebralis: identification of a cathepsin Z-like protease gene (MyxCP-1) expressed during parasite development in rainbow trout, Oncorhynchus mykiss.

Cysteine proteases are essential to the biological function of parasitic organisms and are gaining interest as the target of chemotherapeutics aimed at their control. We report a cysteine protease gene from the myxozoan Myxobolus cerebralis, the cause of whirling disease in salmonid fish. The mature gene (MyxCP-1) encodes a 248-amino acid polypeptide that includes catalytic residues similar to the papain family of cysteine proteases.

Observations on the life stages of Sphaerothecum destruens n. g., n. sp., a mesomycetozoean fish pathogen formerly referred to as the rosette agent [correction].

The rosette agent is an obligate intracellular parasite that causes morbidity and mortality in salmonid fish. In laboratory cultures, the spore stage (2-6 microm diam.) replicates in a salmonid cell line by sequential asexual division, giving rise to daughter cells.

Molecular comparison of isolates of an emerging fish pathogen, koi herpesvirus, and the effect of water temperature on mortality of experimentally infected koi.

Koi herpesvirus (KHV) has been associated with devastating losses of common carp (Cyprinus carpio carpio) and koi (Cyprinus carpio koi) in North America, Europe, Israel and Asia. A comparison of virion polypeptides and genomic restriction fragments of seven geographically diverse isolates of KHV indicated that with one exception they represented a homogeneous group. A principal environmental factor influencing the onset and severity of disease is water temperature.

Systemic herpes-like virus in catfish Ictalurus melas (Italy) differs from Ictalurid herpesvirus 1 (North America).

A herpesvirus was isolated during 2 occurrences of mass mortality among adult catfish Ictalurus melas raised in different farms in northern Italy. The agent replicated in the channel catfish ovary (CCO) cell line from channel catfish I. punctatus, inducing a cytopathic effect similar to that caused by Ictalurid herpesvirus 1 (also referred to as channel catfish herpesvirus, CCV).

Initial characteristics of koi herpesvirus and development of a polymerase chain reaction assay to detect the virus in koi, Cyprinus carpio koi.

Since 1998, episodes of mass mortality have occurred in populations of common carp Cyprinus carpio carpio in Israel and in populations of koi Cyprinus carpio koi in Israel and the USA. A herpesvirus isolated from infected fish has been shown in experimental studies to induce disease and mortality similar to those observed in outbreaks at infected farms. Initial characteristics of the virus show that it is clearly different from Herpesvirus cyprini (CHV), the most commonly known herpesvirus from cyprinid fish.