Viruses and renal carcinoma of Rana pipiens. VII. Propagation of a herpes-type frog virus

A quantitative-PCR based method to estimate ranavirus viral load following normalisation by reference to an ultraconserved vertebrate target

Ranaviruses are important pathogens of amphibians, reptiles and fish. To meet the need for an analytical method for generating normalised and comparable infection data for these diverse host species, two standard-curve based quantitative-PCR (qPCR) assays were developed enabling viral load estimation across these host groups. A viral qPCR targeting the major capsid protein (MCP) gene was developed which was specific to amphibian-associated ranaviruses with high analytical sensitivity (lower limit of detection: 4.23 plasmid standard copies per reaction) and high reproducibility across a wide dynamic range (coefficient of variation below 3.82% from 3 to 3×10⁸ standard copies per reaction). The comparative sensitivity of the viral qPCR was 100% (n=78) based on agreement with an established end-point PCR. Comparative specificity with the end-point PCR was also 100% (n=94) using samples from sites with no history of ranavirus infection. To normalise viral quantities, a host qPCR was developed which targeted a single-copy, ultra-conserved non-coding element (UCNE) of vertebrates. Viral and host qPCRs were applied to track ranavirus growth in culture. The two assays offer a robust approach to viral load estimation and the host qPCR can be paired with assays targeting other pathogens to study infection burdens.

Cyprinid Herpesvirus 3: An Archetype of Fish Alloherpesviruses

The order Herpesvirales encompasses viruses that share structural, genetic, and biological properties. However, members of this order infect hosts ranging from molluscs to humans. It is currently divided into three phylogenetically related families. The Alloherpesviridae family contains viruses infecting fish and amphibians. There are 12 alloherpesviruses described to date, 10 of which infect fish. Over the last decade, cyprinid herpesvirus 3 (CyHV-3) infecting common and koi carp has emerged as the archetype of fish alloherpesviruses. Since its first description in the late 1990s, this virus has induced important economic losses in common and koi carp worldwide. It has also had negative environmental implications by affecting wild carp populations. These negative impacts and the importance of the host species have stimulated studies aimed at developing diagnostic and prophylactic tools. Unexpectedly, the data generated by these applied studies have stimulated interest in CyHV-3 as a model for fundamental research. This review intends to provide a complete overview of the knowledge currently available on CyHV-3.

Herpesviruses that infect fish

Herpesviruses are host specific pathogens that are widespread among vertebrates. Genome sequence data demonstrate that most herpesviruses of fish and amphibians are grouped together (family Alloherpesviridae) and are distantly related to herpesviruses of reptiles, birds and mammals (family Herpesviridae). Yet, many of the biological processes of members of the order Herpesvirales are similar. Among the conserved characteristics are the virion structure, replication process, the ability to establish long term latency and the manipulation of the host immune response. Many of the similar processes may be due to convergent evolution. This overview of identified herpesviruses of fish discusses the diseases that alloherpesviruses cause, the biology of these viruses and the host-pathogen interactions. Much of our knowledge on the biology of Alloherpesvirdae is derived from research with two species: Ictalurid herpesvirus 1 (channel catfish virus) and Cyprinid herpesvirus 3 (koi herpesvirus).

Genome sequences of two frog herpesviruses

The sequences of two frog herpesviruses, Ranid herpesvirus 1 and Ranid herpesvirus 2, were determined. They are respectively 220 859 and 231 801 bp in size and contain 132 and 147 predicted genes. The genomes are related most closely in the central regions, where 40 genes are conserved convincingly. Nineteen of these genes are also conserved in a fish herpesvirus, Ictalurid herpesvirus 1. The terminal regions of the genomes are largely not conserved and contain many of the 15 families of related genes present in each genome. The frog herpesviruses are unique among sequenced herpesviruses in that the three exons of the gene encoding the putative ATPase subunit of terminase are not specified by the same DNA strand and in that they encode a putative DNA (cytosine-5-)-methyltransferase and have extensively methylated genomes.

Viruses and renal carcinoma of Rana pipiens. XV. The presence of virus-associated membrane antigen(s) on Lucké tumor cells

Virus-specific antigens were detected in Lucké tumor cells by indirect immunofluorescence using antiserum prepared against Lucké herpesvirus. Intracellular fluorescence, both cytoplasmic and nuclear, was observed only in acetone:methanol-fixed tumor cells that contained herpesvirus detected by electron microscopy. The number of positive cells correlated well with the number of cells containing virus. In contrast, both virus-containing and virus-free cells exhibited membrane fluorescence when viable unfixed tumor cells were tested. A striking reduction in the number of membrane fluorescent cells was observed with an increase in the length of time that tumor cells were in primary culture. No reaction was observed with a variety of normal R. pipiens cells. Absorption of the antiserum with normal frog kidney tissue had no effect on the number of positive cells whereas absorption with virus-free tumor reduced the reaction; absorption with virus-containing tumor eliminated it. These findings provide the first demonstration that the Lucké herpesvirus genome resident in virus-free tumor cells expresses a virus-associated membrane antigen(s).

Replication of herpesvirus of turkeys in chick fibroblasts

An ultrastructural study of chick embryo fibroblasts infected with herpesvirus of turkeys (HVT) revealed that infection produced degenerative effects in the cells ranging from alteration of cellular structures to complete lysis of the cells. Infection was indicated by margination of the nuclear chromatin, the presence of nuclear and cytoplasmic virions, destruction of mitochondria, loss of rough and smooth endoplasmic reticulum, and polykaryocytosis. Viruses entered the cell by penetrating the cytoplasmic membrane, and replication took place within the nucleus. Small nuclear particles observed as aggregates in the presence of few herpesvirions appeared to be a part of the replication of the virus. Viruses were released from the cell nucleus either naked or enveloped. Where karyolysis occurred, naked viruses were released as the karyoplasm diffused into the cytoplasm. Enveloped viruses were not observed leaving the nucleus, but it appeared that departure could have occurred by the budding of the viruses through the nuclear membrane. Where complete lysis of the cells occurred, the naked viruses were released into the extracellular fluid. Enveloped viruses were observed only in intact cells. Viruses which were observed extracellularly were naked viruses, and those that were observed entering the cell by penetrating the cytoplasmic membrane were also naked. This evidence suggests that in vitro HVT does not require the envelope to be infective.

The presence of the Lucké herpesvirus genome in induced tadpole tumors and its oncogenicity: Koch-Henle postulates fulfilled

Herpesvirus extracted from a naturally occurring frog renal carcinoma (Lucké tumor) induced virus-free Lucké tumors in developing frogs. Herpesvirus recovered from an induced tumor after incubation at low temperature of tumor fragments cultured in vitro was oncogenic when injected into developing frog embryos. With the exception of the "pure culture" requirement, this experiment fulfills Koch-Henle postulates for the identification of the causative agent of the Lucké tumor.