Megalocytivirus and Other Members of the Family Iridoviridae in Finfish: A Review of the Etiology, Epidemiology, Diagnosis, Prevention and Control

Abstract

Aquaculture has expanded to become the fastest growing food-producing sector in the world. However, its expansion has come under threat due to an increase in diseases caused by pathogens such as iridoviruses commonly found in aquatic environments used for fish farming. Of the seven members belonging to the family Iridoviridae, the three genera causing diseases in fish comprise ranaviruses, lymphocystiviruses and megalocytiviruses. These three genera are serious impediments to the expansion of global aquaculture because of their tropism for a wide range of farmed-fish species in which they cause high mortality. As economic losses caused by these iridoviruses in aquaculture continue to rise, the urgent need for effective control strategies increases. As a consequence, these viruses have attracted a lot of research interest in recent years. The functional role of some of the genes that form the structure of iridoviruses has not been elucidated. There is a lack of information on the predisposing factors leading to iridovirus infections in fish, an absence of information on the risk factors leading to disease outbreaks, and a lack of data on the chemical and physical properties of iridoviruses needed for the implementation of biosecurity control measures. Thus, the synopsis put forth herein provides an update of knowledge gathered from studies carried out so far aimed at addressing the aforesaid informational gaps. In summary, this review provides an update on the etiology of different iridoviruses infecting finfish and epidemiological factors leading to the occurrence of disease outbreaks. In addition, the review provides an update on the cell lines developed for virus isolation and culture, the diagnostic tools used for virus detection and characterization, the current advances in vaccine development and the use of biosecurity in the control of iridoviruses in aquaculture. Overall, we envision that the information put forth in this review will contribute to developing effective control strategies against iridovirus infections in aquaculture.

Integrated multi-omics analysis reveals liver metabolic reprogramming by fish iridovirus and antiviral function of alpha-linolenic acid

“…Iridoviruses are important emerging pathogens that impact ectothermic vertebrates (including fish, frogs, newts, and reptiles) and invertebrates (including insects and crustaceans) worldwide. These viruses have attracted increasing attention due to their role in the decline of amphibian populations and the substantial economic losses they cause in the global aquaculture industry ( Chinchar et al, 2017 ; Qin et al, 2023 ; Zhao et al, 2023 ). According to the International Committee on Taxonomy of Viruses (https://ictv.global/taxonomy), iridoviruses are currently divided into seven genera, including Iridovirus , Megalocytivirus , Ranavirus , Lymphocystivirus , Chloriridovirus , Decapodiridovirus , and Daphniairidovirus ( Chen et al, 2019 ; Qin et al, 2023 ).…”

“…These viruses have attracted increasing attention due to their role in the decline of amphibian populations and the substantial economic losses they cause in the global aquaculture industry ( Chinchar et al, 2017 ; Qin et al, 2023 ; Zhao et al, 2023 ). According to the International Committee on Taxonomy of Viruses (https://ictv.global/taxonomy), iridoviruses are currently divided into seven genera, including Iridovirus , Megalocytivirus , Ranavirus , Lymphocystivirus , Chloriridovirus , Decapodiridovirus , and Daphniairidovirus ( Chen et al, 2019 ; Qin et al, 2023 ). As a typical agent of fish iridovirus, the Singapore grouper iridovirus (SGIV), belonging to the genus Ranavirus , was initially isolated from diseased groupers ( Epinephelus tauvina ) and has caused significant mortality and economic losses in grouper aquaculture ( Qin et al, 2003 ).…”

Molecular docking and simulation studies of Chloroquine, Rimantadine and CAP-1 as potential repurposed antivirals for decapod iridescent virus 1 (DIV1)

“…MCP is a crucial component of the viral capsid, which is the protective outer shell of the virus [ 15 , 16 ]. It is responsible for forming the structural framework of the viral particle in several viruses, including DIV1 [17] , [18] , [19] . By targeting structural proteins like MCP, it is possible to disrupt multiple stages of the viral lifecycle.…”

“…In the case of DIV1, interfering with MCP can impair viral assembly, maturation, and, ultimately, the virus's ability to infect host cells. Furthermore, MCP is often a conserved protein within a viral species, making it a constant and reliable target for drug development [ 17 , 20 ]. This consistency minimizes the probability of resistance forming quickly, which is a concern in the development of antiviral drugs.…”

Molecular epidemiology of Megalocytivirus in freshwater angelfish (Pterophyllum scalare) from Johor, Malaysia

“…Infectious spleen and kidney necrosis virus can remain infective even when isolated and kept under −70°C for >8 months and 40°C for 30 min, but the virus was inactivated when it was isolated and kept under 50°C for 30 min [16]. Therefore, Megalocytivirus can remain active throughout the year at optimum temperatures and contribute to the occurrence of disease outbreaks [17]. Few studies have reported the effect of temperature on Megalocytivirus, specifically in ornamental fish [8].…”