Advances in Viral Aquatic Animal Disease Knowledge: The Molecular Methods’ Contribution

Abstract

Aquaculture is the fastest-growing food-producing sector, with a global production of 122.6 million tonnes in 2020. Nonetheless, aquatic animal production can be hampered by the occurrence of viral diseases. Furthermore, intensive farming conditions and an increasing number of reared fish species have boosted the number of aquatic animals’ pathogens that researchers have to deal with, requiring the quick development of new detection and study methods for novel unknown pathogens. In this respect, the molecular tools have significantly contributed to investigating thoroughly the structural constituents of fish viruses and providing efficient detection methods. For instance, next-generation sequencing has been crucial in reassignment to the correct taxonomic family, the sturgeon nucleo-cytoplasmic large DNA viruses, a group of viruses historically known, but mistakenly considered as iridoviruses. Further methods such as in situ hybridisation allowed objectifying the role played by the pathogen in the determinism of disease, as the cyprinid herpesvirus 2, ostreid herpesvirus 1 and betanodaviruses. Often, a combination of molecular techniques is crucial to understanding the viral role, especially when the virus is detected in a new aquatic animal species. With this paper, the authors would critically revise the scientific literature, dealing with the molecular techniques employed hitherto to study the most relevant finfish and shellfish viral pathogens.

Viral Diversity in Samples of Freshwater Gastropods Benedictia baicalensis (Caenogastropoda: Benedictiidae) Revealed by Total RNA-Sequencing

“…TPNNV, together with other representatives of the Betanodavirus genus, is known to infect over 60 different species of marine and freshwater fish, causing viral nervous necrosis, also known as viral encephalopathy and retinopathy. This disease was first described in the late 1980s; it causes fish mortality outbreaks and large economic losses to the marine aquaculture industry worldwide [57,58].…”

“…In the phylogenetic analysis of RdRp domains, scaffold BM_14418 (close to Tiger puffer nervous necrosis virus) clustered with other betanodaviruses (MAGs) from bivalve mollusks (Figure 5). The bioaccumulation of another fish-pathogenic betanodavirus, Red-spotted grouper nervous necrosis virus (RGNNV), in hepatopancreatic tissue of manila clam Ruditapes philippinarum, and the ability to release infectious viral particles via fecal matter and filtered water was also shown [58]. Reservoirs of 'nervous necrosis viruses' were reported in different mollusks (bivalves, gastropods and cephalopods) and other marine invertebrate species (crabs, shrimps, artemias and rotifers) in waters of South Korea, Japan and China, in the European Atlantic and Mediterranean waters [59].…”

Cross-sectional study on prevalence of theileriosis in Kendrapada sheep, Odisha

“…Both light microscopy and serological approaches may face challenges in distinguishing between different species due to structural resemblances. To overcome the above limitations, molecular techniques have become crucial and extensively employed for identifying diseases, carrier status and sub-clinical infections (Volpe et al 2023;Liu et al 2023;Airs et al 2023). Due to the recent surge in infections and mortality among Kendrapada sheep, causing signi cant losses in productivity, the current study aims to investigate the various haemo protozoan parasites affecting Kendrapada sheep in its native area, speci cally Kendrapara district.…”