Elevation of temperature and crowding trigger acute viral nervous necrosis in zebra fish, <i>Brachydanio rerio</i> (Hamilton‐Buchanan), subclinically infected with betanodavirus

Lee

Journal of Fish Diseases

2016

The genus Megalocytivirus is known to infect a wide range of cultured marine fish. In this study, we examined the pathogenicity of FLIV (Megalocytivirus from olive flounder, genotype III) and RBIV (Megalocytivirus from rock bream, genotype I) to their homologous and heterologous host species. Olive flounder (7.5 ± 1.3 cm) injected with FLIV [major capsid protein (MCP) gene copies, 6.8 × 10 -6.5 × 10 /fish] at 24 °C did not die until 90 days post-infection (dpi). The average virus replication in the spleen peaked (1.27 × 10 /fish) at 20 dpi. Rock bream (6.5 ± 1.5 cm) injected with FLIV (8.8 × 10 and 6.5 × 10 /fish of MCP copies) showed no mortality until 50 dpi. The rock bream that survived after FLIV infection were rechallenged with RBIV at 50 dpi had 100% mortality, showing that there is no cross-protection between FLIV and RBIV. Temperature shifting (26 °C and 20 °C at 12 h intervals) did not cause FLIV-specific mortality into olive flounder, but higher virus copies were observed in the fish exposed to higher stocking density. This study demonstrates that FLIV and RBIV have different antigenic and pathogenic characteristics and that FLIV has low pathogenicity to olive flounder.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Low pathogenicity of flounder iridovirus (FLIV) and the absence of cross‐protection between FLIV and rock bream iridovirus

Lee

Journal of Fish Diseases

2016

“…The association of disease outbreaks with seasonality (May to October, when the water has relatively high temperatures) further indicates the involvement of an infectious agent, since water temperature affects the emergence of a wide range of parasitic, bacterial, and viral diseases of fish (14,(29)(30)(31)(32)(33)(34).…”

Section: Discussionmentioning

confidence: 99%

“…Examples for the influence of the environmental conditions on disease progression (33) include piscine rhabdoviruses, in which classical acute hemorrhagic septicemias (35,36) may change to subacute, chronic, or nervous forms (9,(37)(38)(39)(40)(41), and these are seldom difficult to visualize and monitor in open waters (42). Likewise, the influence of harsh husbandry conditions in close community on the severity of the disease was documented for VNN (14,43).…”

Section: Discussionmentioning

confidence: 99%

Identification of a Novel RNA Virus Lethal to Tilapia

Eyngor¹,

et al. 2014

gTilapines are important for the sustainability of ecological systems and serve as the second most important group of farmed fish worldwide. Significant mortality of wild and cultured tilapia has been observed recently in Israel. The etiological agent of this disease, a novel RNA virus, is described here, and procedures allowing its isolation and detection are revealed. The virus, denominated tilapia lake virus (TiLV), was propagated in primary tilapia brain cells or in an E-11 cell line, and it induced a cytopathic effect at 5 to 10 days postinfection. Electron microscopy revealed enveloped icosahedral particles of 55 to 75 nm. Low-passage TiLV, injected intraperitoneally in tilapia, induced a disease resembling the natural disease, which typically presents with lethargy, ocular alterations, and skin erosions, with >80% mortality. Histological changes included congestion of the internal organs (kidneys and brain) with foci of gliosis and perivascular cuffing of lymphocytes in the brain cortex; ocular inflammation included endophthalmitis and cataractous changes of the lens. The cohabitation of healthy and diseased fish demonstrated that the disease is contagious and that mortalities (80 to 100%) occur within a few days. Fish surviving the initial mortality were immune to further TiLV infections, suggesting the mounting of a protective immune response. Screening cDNA libraries identified a TiLV-specific sequence, allowing the design of a PCR-based diagnostic test. This test enables the specific identification of TiLV in tilapines and should help control the spread of this virus worldwide.

Journal of Fish Diseases

“…Hodneland, Garca, Balbuena, Zarza, and Fouz (2011) According to this, we should have expected to see higher levels of mortality in the present study, with the measured mean brain Ct values of 13.12 and 9.92 for IM-and immersion-infected fish, respectively. Although there are indications that an active infection was present, with replicating virus in infected brains (e.g., the number of infective particles increased between 7 and 15 dpi from 10 6.83 to 10 9.63 TCID 50 /ml in the immersion-infected fish), we postulate that the fish from both infection groups were sub-clinically infected with the virus, resulting in the absence of clinical signs of the disease with only low levels of mortality resulting (Binesh, 2014). This is supported by the fact that Hodneland et al (2011) observed survivors from a prior VER outbreak, with brain Ct values of 11.6-31.0, dying only when water temperatures increased, a known trigger for VER outbreaks, indicating their carrier status for Betanodavirus.…”

Section: Discussionmentioning

confidence: 93%

Detection of Betanodavirus in experimentally infected European seabass (Dicentrarchus labrax, Linnaeus 1758) using non‐lethal sampling methods

Ferreira

Costa

Macchia

et al. 2019

One of the major disease threats affecting the Mediterranean aquaculture industry is viral encephalopathy and retinopathy (VER). The target organs for Betanodavirus detection are the brain and eyes, obtained through lethal sampling. This study aimed to evaluate the efficacy and suitability of non‐lethal samples for detecting Betanodavirus in European seabass (Dicentrarchus labrax). European seabass juveniles were infected with Betanodavirus, by either an intramuscular injection or immersion (107 TCID50/ml and 106 TCID50/ml, respectively), and samples collected 7, 15 and 30 days post‐infection (dpi). The brain was collected as a lethal sample, and gills, caudal fin and blood as non‐lethal tissues for detecting Betanodavirus by quantitative reverse transcription PCR (RT‐qPCR). The presence of virus in non‐lethal tissues was inconsistent, with lower viral loads than in the brain. For blood, higher viral loads were detected in intramuscular‐infected fish at 15 dpi until the end of the challenge. Serum antibodies against Betanodavirus were assessed using an enzyme‐linked immunosorbent assay (ELISA). Antibodies were detected as early as 7 dpi, with higher mean antibody titres at 15 and 30 dpi. The presence of Betanodavirus‐specific antibodies indicates that this is a suitable evaluation method for detecting early stages of the infection.