Investigation of latent infections caused by cyprinid herpesvirus 3 in koi ( Cyprinus carpio) in southern China

A review of latency in the Alloherpesviridae family

The ability to impact the immune response of the host has been recognized as essential for the success of a virus during infection. A few groups of viruses can combine these immunomodulatory mechanisms with specific patterns of their own transcriptional and replication regulation to achieve persistence within the host long term. The Herpesvirales order is one of those groups and the resultant state is known as latency. Throughout the years, latency has been studied in many host-herpesvirus models to attempt to understand the complex and profound effects of this state on the host's systems, and in the hopes of deciphering a way to eliminate the latent state from survivors of the primary infection. Most studies of herpesvirus latency have been conducted on mammalian host species, but this review summarizes the data available regarding herpesviruses in fish species and their latent state. As the field of aquatic animal health research continues to advance, the elucidation of these complex mechanisms will be crucial for disease control, prevention, and treatment.

Biosecurity and the ornamental fish trade: A stakeholder perspective in England

The freshwater and marine ornamental fish industry is a primary route of hazard introduction and emergence, including aquatic animal diseases and non-native species. Prevention measures are key to reducing the risk of hazard incursion and establishment, but there is currently little understanding of the biosecurity practices and hazard responses implemented at post-border stages of the ornamental fish supply chain. This study addresses this knowledge gap, using questionnaires to collate information on actual biosecurity behaviours and hazard responses practised by ornamental fish retailers and hobbyist communities in England. Actual behaviours varied considerably within retailers and hobbyists, suggesting that reliance on preventative practices by individuals in the post-border stages of the ornamental fish supply chain is likely to be ineffective in minimizing the risk of hazard incursion and establishment. Resources should be allocated towards improving and enforcing robust pre- and at-border control measures, such as risk-based surveillance of ornamental fish imports at border controls. In addition, these findings should be used to implement targeted awareness-raising campaigns and help create directed training on biosecurity practices for individuals involved in the post-border stages of the ornamental supply chain.

Comparative assessment of live cyprinid and salmonid movement networks in England and Wales

Disease poses a significant threat to aquaculture. While there are a number of factors contributing to pathogen transmission risk, movement of live fish is considered the most important. Understanding live fish movement patterns for different aquaculture sectors is therefore crucial to predicting disease occurrence and necessary for the development of effective, risk-based biosecurity, surveillance and containment policies. However, despite this, our understanding of live movement patterns of key aquaculture species, namely salmonids and cyprinids, within England and Wales remains limited. In this study, networks reflecting live fish movements associated with the cyprinid and salmonid sectors in England and Wales were constructed. The structure, composition and key attributes of each network were examined and compared to provide insight into the nature of trading patterns and connectedness, as well as highlight sites at a high risk of spreading disease. Connectivity at both site and catchment level was considered to facilitate understanding at different resolutions, providing further insight into disease outbreaks, with industry wide implications. The study highlighted that connectivity through live fish movements was extensive for both industries. The salmonid and cyprinid networks comprised 2533 and 3645 nodes, with a network density of 5.81 × 10^-4 and 4.2 × 10^-4, respectively. The maximum network reach of 2392 in the salmonid network was higher, both in absolute terms and as a proportion of the overall network, compared to maximum network reach of 2085 in the cyprinid network. However, in contrast, the number of sites in the cyprinid network with a network reach greater than one was 513, compared to 171 in the salmonid network. Patterns of connectivity indicated potential for more frequent yet smaller scale disease outbreaks in the cyprinid industry and less frequent but larger scale outbreaks in the salmonid industry. Further, high connectivity between river catchments within both networks was shown, posing challenges for zoning at the catchment level for the purpose of disease management. In addition to providing insight into pathogen transmission and epidemic potential within the salmonid and cyprinid networks, the study highlights the utility of network analysis, and the value of accessible, accurate live fish movement data in this context. The application of outputs from this study, and network analysis methodology, to inform future disease surveillance and control policies, both within England and Wales and more broadly, is discussed.

Koi herpesvirus disease outbreak: Input for the implementation of a surveillance program in South Tyrol - Italy

A severe episode of high and abnormal mortality was observed in the population of Cyprinus carpio of Lake Caldaro (South Tyrol, Italy) in summer 2016. The diagnostic investigation carried out led to the identification of Koi Herpesvirus (KHV) as the etiologic agent. Following this disease outbreak and its socio-economic consequences, the local authorities, in agreement with the local Fishing Association, decided to implement a surveillance program for the achievement of KHV-free health status (Category I) in the Province, in accordance to the Implementing Decision (EU) 2015/1554. The selected area was a defined geographical compartment (the Monticolo lakes compartment, South Tyrol, Italy), which is located near Lake Caldaro, where the Koi Herpesvirus disease (KHVD) outbreak had occurred. This area is of particular interest because it supplies other water bodies with juvenile C. carpio individuals; with the achievement of a KHV-free health status, South Tyrol could possibly become independent in the breeding of this fish species. Suitable samples were collected and processed during a two-year period in order to detect the presence/absence of KHV. The same samples were tested for other viruses that can affect carp, namely spring viraemia of carp (SVCV) and carp edema virus (CEV). According to the results, the authors conclude that the Monticolo lakes area should be classified as KHV-free, as no sample has tested positively for the presence of this specific virus (KHV).

Oral vaccination using Artemia coated with recombinant Saccharomyces cerevisiae expressing cyprinid herpesvirus-3 envelope antigen induces protective immunity in common carp (Cyprinus carpio var. Jian) larvae

Cyprinid herpesvirus 3 (CyHV-3) is the etiological agent of koi herpersvirus disease (KHVD), which causes serious economic losses in global common carp and ornamental koi carp production of larvae as well as adult type fish. To control KHVD, vaccines against CyHV-3 utilizing different immunization routes have been developed, among them, oral vaccination is the most desirable method to prevent fish diseases occurring at the early larval stage. Here, we developed an oral subunit vaccine through the Saccharomyces cerevisiae cell surface display of CyHV-3 envelope protein pORF65, then, the recombinant yeast fed to Artemia which served as bio-encapsulation vector by subsequently feeding the common carp (Cyprinus carpio var. Jian) larvae. The fluorescent observation showed that the Artemia and S. cerevisiae could deliver intact antigen to the hindgut of carp larvae suggesting the possibility of the vector for oral immunization. On this basis, after three immunizations at a week interval, the oral vaccine induced high level of specific anti-pORF65 antibody. Meanwhile, a significant difference of immune-related genes expression occurred including cxca, IL-1β, IFN-a1, lysozyme, IgM and CD8α between vaccined group and blank control group. In addition, 30% of relative percent survival of carp larvae after immunization was obtained post the animal infection assay, offered an certain immune protection. Our results indicated that the oral pORF65 subunit vaccine bioencapsulated in Artemia induced the activation of immune response and high level of antibodies, which could be served as an oral vaccine candidate for the prevention of CyHV-3 infection.