Infectious Pancreatic Necrosis (IPN) is a highly contagious systemic birnavirus disease of young fish of Salmonid species held under intensive rearing conditions. The disease most characteristically occurs in rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), Atlantic salmon (Salmo salar) and several Pacific salmon species (Oncorhynchus spp.).
It mostly occurs under intensive rearing conditions in Salmonids hatcheries or in Post-Smolt Atlantic salmon in sea-cages.
The IPN virus is a birnavirus. The original serotype isolated from rainbow trout fingerlings is called VR-299. Since then, several serotypes have been identified and, in 1995, two serogroups, A and B, were established, each containing serotypes with different geographic origins. The most frequently found and virulent serotype is the Sp serotype.
The lethality of the virus depends on the strain, the species and age of the fish. Predisposing stress-inducing factors, such as first feeding, high stocking density, fluctuations in water temperature, salinity and handling, are believed to favour the onset of clinical disease. Outbreaks can occur all year round, at water temperatures as low as 4 ° C and as high as 18 °C.
Infectious Pancreatic Necrosis virus is a bi-segmented double-stranded RNA virus of the family Birnaviridae. At least nine serotypes exist. Susceptibility decreases with increasing age, with complete resistance to clinical disease in fry/fingerlings being reached at about 1500 degree-days (value obtained by multiplying the age in days by the average temperature during the lifespan) except for Atlantic salmon Smolts, which develop the disease within weeks following transfer from freshwater to seawater (Merck - Infectious Pancreatic Necrosis Virus).
Chinook salmon embryo cells (CHSE-214) were cultured in Minimal Essential Medium (MEM, Gibco, Cat No: C11095500BT) including 10% fetal bovine serum (FBS, Gibco, Cat No: 10099141) at 18 °C, and was used to amplify IPNV at 15 °C in vitro in this study. (Duan et al., 2022)
f. Immunization Route
Intraperitoneal injection (i.p.)
g. Description
IPNV isolate GS2019-4 inactivated vaccine could induce a non-specific and specific immune response in rainbow trout, which are responsible for the anti-IPNV ability at an early and late stage after immunization. (Duan et al., 2022)
h.
Fish Response
Vaccination Protocol:
Rainbow trout (n = 30) were intraperitoneally injected with the inactivated virus with a dose of 200 μl per fish (2.50 × 10^5.0 PFU). The injected fish were maintained in the circulating aquarium (15 °C), fed a commercial pelleted diet, and the healthy condition was observed for 30 days. (Duan et al., 2022)
Immune Response:
The viral loads ratio (PBS group/immunization group) was calculated to present the antivirus effect of the IPN vaccine. The higher the ratio is, the stronger the antiviral effect is. Viral loads in immunized rainbow trout at each time point were significantly lower than that in the PBS group (Table 2), indicating that the vaccination function in resistance to virus infection. The strongest antiviral effect was observed on 30 d.p.i, the viral loads ratio at this time point was significantly higher than those on other time points (p < 0.05), and the mean viral loads ratio at this time point was 1.00 × 10^4.73 (53703.17) folds. The weakest antiviral effect was observed on 3 d.p.i, and the viral loads ratio was 1.0 × 100.66 (4.57 folds), but the viral loads in the immunized group were still significantly lower than that in the negative control group at this time point (p < 0.05). (Duan et al., 2022)
Challenge Protocol:
Rainbow trout (n = 60) were intraperitoneally injected with IPNV at the dose of 10 μl per fish (1.25 × 10^4.0 PFU), and the rainbow trout injected with phosphate buffer solution (PBS) were used as the negative control. (Duan et al., 2022)
Efficacy:
The viral loads in the immunized rainbow trout were significantly decreased, indicating that the vaccine had good immune protection. (Duan et al., 2022)
