Genotyping of infectious pancreatic necrosis virus isolates from Mexico state

Dynamic Distribution of Infectious Pancreatic Necrosis Virus (IPNV) Strains of Genogroups 1, 5, and 7 after Intraperitoneal Administration in Rainbow Trout (Oncorhynchus mykiss)

Infectious pancreatic necrosis virus (IPNV) is the causative agent of rainbow trout (Oncorhynchus mykiss) IPN and causes significant loss of fingerlings. The currently prevalent IPNV genogroups in China are genogroups 1 and 5. However, in this study, we isolated and identified a novel IPNV, IPNV-P202019, which belonged to genogroup 7. Here, a total of 200 specific-pathogen-free rainbow trout (10 g average weight) were divided randomly into four groups to investigate the distribution of different IPNV strains (genogroups 1, 5, and 7) in 9 tissues of rainbow trout by means of intraperitoneal (ip) injection. Fish in each group were monitored after 3-, 7-, 14-, 21- and 28- days post-infection (dpi). The study showed no mortality in all groups. The distribution of IPNV genogroups 1 and 5 was similar in different tissues and had a higher number of viral loads after 3, 7, or 14 dpi. However, the distribution of IPNV genogroup 7 was detected particularly in the spleen, head kidney, and feces and had a lower number of viral loads. The results of this study provide valid data for the distribution of IPNV in rainbow trout tissues and showed that IPNV genogroups 1 and 5 were still the prevalent genogroups of IPNV in China. Although rainbow trout carried IPNV genogroup 7, the viral load was too low to be pathogenic.

An inactivated vaccine against infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss)

Infectious pancreatic necrosis virus (IPNV), belonging to the genus Aquabirnavirus within the family Birnaviridae, causes huge economic loss to the global salmonid industry every year. Recently, outbreaks of disease caused by genogroup I IPNV were found in many rainbow trout (Oncorhynchus mykiss) farms worldwide. An inactivated vaccine was prepared using a genogroup I IPNV isolate with an optimized procedure as incubation with β-propanolactone (BPL) at the final concentration of 0.5% at room temperature for 48 h. The inactivated vaccine was used to immunize rainbow trout, and the protection efficiency was evaluated by viral loads determination, immune-related genes quantification, and neutralizing antibody tests. The viral loads in immunized rainbow trout were significantly decreased and the strongest antiviral effect was observed on 30 days post-immunization (d.p.i). The expression of innate immune-related genes IFN-1, and Mx-1 genes were significantly up-regulated on 3, 7, and 15 d.p.i (p < 0.05), and adaptive immune-related genes CD4, CD8, and IgM genes were significantly up-regulated on 15 and 30 d.p.i (p < 0.05). Neutralizing antibodies were firstly detected on 30 d.p.i and the highest titer was observed on 45 d.p.i, which began to decrease on 60 d.p.i, but was still significantly higher than that in negative control fish. The results indicated that the vaccine prepared in this study could stimulate the non-specific and specific immune response and provide significant immune protection to the vaccinated rainbow trout.

Virulence of infectious pancreatic necrosis virus (IPNV) isolates from Mexico

Infectious pancreatic necrosis virus (IPNV) causes economic losses in Mexican rainbow trout industry. In this study, virulence and genetic fingerprints of Mexican IPNV isolates was investigated for the first time. Two Mexican IPNV isolates were analyzed in rainbow trout fry and the Sp strain was included as high virulence. One of the Mexican IPNV isolate was obtained from diseased fish and the other from fish without clinical signs. The infection was performed using a standardized immersion. Clinical signs were observed at 4 days post infection in fry group infected with strain Sp, two days earlier than in trout infected with IPNV isolates Mexican. Severe lesions were found in 100% of the individuals of Sp group, but only in 25% of each isolated Mexican group. Results suggest that Mexican IPNV isolates are pathogenic, but less virulent than strain Sp. The amino acid motif residues of both Mexican isolates, corresponded to a subclinical disease. Nevertheless, the accumulated motility observed in the field, suggest that other factors play a role in the virulence of the disease.

Distribution of Infectious Pancreatic Necrosis Virus (IPNV) Based on Surveillance Programs in Freshwater Trout Farms of Mexico

Diagnostic testing was performed between 2000 and 2012 to determine the distribution of infectious pancreatic necrosis virus (IPNV) in the main states of the Mexican Republic with freshwater Rainbow Trout Oncorhynchus mykiss (Walbaum) farms. This virus was positively identified from Rainbow Trout farms in seven of the eight states assessed. Due to nonnormal data distribution, a logistic regression model was applied for statistical analysis, the results of which indicated that virus prevalence was variable between states, with moderate but significant differences. Regarding the time periods evaluated, IPNV prevalence was higher during the first years of the study. The susceptible, infected, removed model was used to examine this phenomenon, which indicated that the decreased prevalence during the latter years of the study could be associated with a real elimination of the infection. The information of the cases analyzed also suggests a relationship with the irregularity in the submission of samples to the laboratory and emphasizes other factors that have contributed to the transmission of IPNV throughout the country. Received November 10, 2014; accepted December 5, 2015.

Molecular characterization of Tasmanian aquabirnaviruses from 1998 to 2013

Tasmanian aquabirnaviruses (TABVs) have been isolated intermittently since 1998 from healthy Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss farmed in Macquarie Harbour, Tasmania, Australia. However, beginning in 2011, TABVs have been isolated from rainbow trout in association with mortality events. To determine if recent molecular changes in TABV were contributing to increased mortalities, next generation sequencing was undertaken on 14 TABVs isolated from 1998 to 2013. Sequencing of both genome segments and analysis of the 5 viral proteins they encode revealed that minimal changes had occurred in the past 15 yr. Of the amino acid changes detected only 1, alanine to aspartic acid at position 139 of the minor structural VP3 protein, was unique to the recent disease events. The most dramatic changes observed were in the length of the non-structural VP5 protein varying from 43 to 133 amino acids. However, the amino acid substitution in VP3 and variable VP5 length were unlikely to have resulted in increased TABV pathogenicity. The genome of a novel Australian aquabirnavirus, Victorian trout aquabirnavirus (VTAB) was also sequenced and compared to TABV isolates.

Molecular characterization of the VP2 gene of infectious pancreatic necrosis virus (IPNV) isolates from Mexico

Infectious pancreatic necrosis virus (IPNV) is one of the most important viruses in the Pacific salmon Oncorhynchus spp., Atlantic Salmon Salmo salar, and Rainbow Trout O. mykiss industry. This virus has been shown to produce high mortality among salmonid fry and juveniles, and survivors might become carriers. Since 2000, IPNV has affected Mexican Rainbow Trout culture, resulting in considerable economic losses. In the current study, molecular characterization of the VP2 gene of a number of Mexican IPNV isolates was done and the virus's phylogenetic relationships to IPNV reference strains were investigated. The phylogenetic analysis indicated that Mexican IPNV isolates are closely related to strains from the United States and Canada and that all Mexican IPNV isolates belong to genogroup 1. Furthermore, low genetic diversity was found between the Mexican isolates (identity, 95.8-99.8% nucleotides and 95.8-99.6% amino acids). The result of the analysis of the amino acid residues found at positions 217, 221, and 247 (alanine, threonine, and glutamic acid, respectively) could be associated with virulence, although the expression of virulence factors is more complex and may be influenced by the agent and host factors. The high percentage of identity among the VP2 genes from geographically distant IPNV isolates and the evidence of wide distribution in the country might have been facilitated by carrier trout. This hypothesis is supported by the identification of the amino acid threonine at position 221 in all Mexican isolates, a factor related to the carrier state for IPNV, as reported by other studies.