Two co-habitation studies with common carp were conducted to determine whether latent infections of koi herpesvirus (KHV) exist. Fish were exposed to KHV using 2 different temperature profiles, which induced low and high initial mortality. Subsequently, certain groups of fish were co-habited with naïve fish while others were not. Koi herpesvirus was reactivated in fish from 3 of the 5 experimental tanks. Reactivation of the virus occurred regardless of the initial mortality associated with the virus or whether fish were co-habited with naïve fish. The reactivation of the virus in our experiments occurred several months after the initial exposure to KHV and appeared to be temperature dependent. KEY WORDS: Koi herpesvirus · KHV · Latent infections · Reactivation · Common carp · Co-habitation Resale or republication not permitted without written consent of the publisherDis Aquat Org 67: [15][16][17][18][19][20][21][22][23] 2005 virus can infect fish and remain in an inactive state until conditions are more favourable.Exposure of carp to KHV at non-permissive temperatures (less than 17°C or greater than 28°C) has been used in the Koi carp industry to induce immunity to the virus (Ronen et al. 2003). Data suggest that at the high end of the non-permissive temperature range, exposed fish develop specific immunity, which upon rechallenge, affords protection. However, there is much debate as to whether this strategy of inducing a 'natural immunity' produces latent infections in fish (Walster 2003), and whether these fish can subsequently transmit the virus to naïve fish.The objectives of this study were to determine whether KHV can persist in common carp after initial virus exposure, and whether the virus can be transmitted to naïve fish by co-habitation. MATERIALS AND METHODSVirus isolate. The UK D-132 Koi herpesvirus isolate (CEFAS) was used to challenge fish in both exposure experiments in this study. The virus was propagated on a koi fin cell line (Hedrick et al. 2000).Fish maintenance. Fig. 1 provides a schematic diagram of the experimental tanks used in this study. All tanks, unless otherwise stated, were on a flow-through system utilizing approximately 2 l min -1 of de-chlorinated bore-hole water. Fish were fed a maintenance diet of 1% bodyweight d -1 throughout the experiment. Fish were monitored for mortalities 2 times d -1 during the course of the study.KHV Exposure 1. Fish: One thousand common carp were purchased from a private farm with no history of KHV. The fish ranged from juveniles (aged ~1 yr), weighing between 25 and 30 g, to older fish that weighed between 150 and 200 g. One hundred fish were placed in each of two 300 l tanks (Tanks 1A and 2A) and served as controls. The 800 remaining fish were placed in a 900 l tank (Tank 1B). Prior to starting the study, fish were brought up to a temperature of 21°C from 10°C (1°C d -1 for 11 d). Ten fish were euthanized prior to exposure to KHV and blood was collected from the caudal vein. Serum was tested for KHV-specific antibodies using an ELISA (se...

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This paper describes effects of temperature on herpes-like virus detection in Pacific oyster Crassostrea gigas larvae held at different temperatures. Intranuclear, intracytoplasmic and extracellular viral particles were observed in velum and mantle connective tissues of oyster larvae reared at 25-26°C. In larvae held at 22-23OC, although nuclear lesions were observed, the presence of viral particles was not detected. Results were obtained for oyster larvae with 4 different parental origins. Herpesvirus infection was found in 3 of the 4 groups of oyster larvae held In the same conditions at the higher temperature.

First observed in 1972 inCrassostrea virginica, herpes-like viruses of bivalves were more recently found to be associated with high mortality rates in other cultured oyster species, such as Crassostrea gigas and Ostrea edulis. The diagnosis of herpes-like virus infections is performed currently by laborious histological and transmission electron microscope examinations. Preparation of specific reagents for use in more amenable diagnostic techniques prompted purification of virus particles and investigation of the viral genome. This paper is the first description of the purification of a virus pathogen from a bivalve mollusc. A procedure was developed which facilitated purification of large amounts of virus particles on the 40-50 % interface of sucrose gradients. Transmission electron microscopy showed that a purified virus suspension contained capsids and enveloped virus particles. High molecular mass viral DNA was extracted, and the genome size was estimated by the summation of the sizes of restriction endonuclease fragments to be approximately 180 kbp. Partial cloning of the virus genome was achieved and the specificity of certain cloned fragments was established by dot blot hybridization.

A simple nylon membrane-based DNA macroarray was developed to genotype spring viraemia of carp virus (SVCV) and related viruses. Twenty-six viruses were genotyped using the array, and the results were confirmed by phylogenetic analysis of a 426 bp partial glycoprotein gene sequence. The array was not only capable of discriminating between the 4 main genogroups of cyprinid vesiculo-type viruses described previously, but also accurately sub-type the SVC viruses assigned to Genogroup I. The assay offers a practical solution for diagnostic laboratories that currently lack a sequencing capability to confirm the nature of PCR products generated in suspected SVCV cases.