Reservoirs of Red-Spotted Grouper Nervous Necrosis Virus (RGNNV) in Squid and Shrimp Species of Northern Alboran Sea.

The production of the aquaculture industry has increased to be equal to that of the world fisheries in recent years. However, aquaculture production faces threats such as infectious diseases. Betanodaviruses induce a neurological disease that affects fish species worldwide and is caused by nervous necrosis virus (NNV). NNV has a nude capsid protecting a bipartite RNA genome that consists of molecules RNA1 and RNA2. Four NNV strains distributed worldwide are discriminated according to sequence homology of the capsid protein encoded by RNA2. Since its first description over 30 years ago, the virus has expanded and reassortant strains have appeared. Preventive treatments prioritize the RGNNV (red-spotted grouper nervous necrosis virus) strain that has the highest optimum temperature for replication and the broadest range of susceptible species. There is strong concern about the spreading of NNV in the mariculture industry through contaminated diet. To surveil natural reservoirs of NNV in the western Mediterranean Sea, we collected invertebrate species in 2015 in the Alboran Sea. We report the detection of the RGNNV strain in two species of cephalopod mollusks (Alloteuthis media and Abralia veranyi), and in one decapod crustacean (Plesionika heterocarpus). According to RNA2 sequences obtained from invertebrate species and reported to date in the Mediterranean Sea, the strain RGNNV is predominant in this semienclosed sea. Neither an ecosystem- nor host-driven distribution of RGNNV were observed in the Mediterranean basin.

A sensitive and specific hyperbranched rolling circle amplification assay and test strip for white spot syndrome virus.

White spot syndrome virus (WSSV) is a global threat to the prawn industry, and there is no simple method for field-based testing of this virus. We designed a padlock probe and primers to the capsid protein gene VP28 of WSSV, and established a hyperbranched rolling circle amplification (HRCA) assay and a corresponding strip-based test. The assay and the test strip both had similar high accuracy and specificity, and their sensitivity was about 10 copies/µL, which is 100 times higher than conventional PCR. In this study, 68 batches of prawns were tested for WSSV with the HRCA assay and test strip, and the results were compared with the PCR assay. The results indicated that both the assay and test strip had accuracy similar to each other and to the PCR results. However, the assay and strip were more sensitive and user-friendly than PCR. Establishment of this method will provide a rapid detection of WSSV and also a basis for field-based detection of animal disease.

Whispovirus.

During the last two decades, a combination of poor management practices and intensive culturing of penaeid shrimp has led to the outbreak of several viral diseases. White spot disease (WSD) is one of the most devastating and it can cause massive death in cultured shrimp. Following its first appearance in 1992-1993 in Asia, this disease spread globally and caused serious economic losses. The causative agent of WSD is white spot syndrome virus (WSSV), which is a large, nonoccluded, enveloped, rod- or elliptical-shaped, dsDNA virus of approximately 300 kbp. WSSV has a very broad host range among crustaceans. It infects many tissues and multiplies in the nucleus of the target cell. WSSV is a lytic virus, and in the late stage of infection, the infected cells disintegrate, causing the destruction of affected tissues. The WSSV genome contains at least 181 ORFs. Most of these encode proteins that show no homology to known proteins, although a few ORFs encode proteins with identifiable features, and these are mainly involved in nucleotide metabolism and DNA replication. Nine homologous regions with highly repetitive sequences occur in the genome. More than 40 structural protein genes have been identified, and other WSSV genes with known functions include immediate early genes, latency-related genes, ubiquitination-related genes, and anti-apoptosis genes. Based on temporal expression profiles, WSSV genes can be classified as early or late genes, and they are regulated as coordinated cascades under the control of different promoters. Both genetic analyses and morphological features reveal the uniqueness of WSSV, and therefore it was recently classified as the sole species of a new monotypic family called Nimaviridae (genus Whispovirus).