The experiment included 162 unvaccinated seawater-adapted Atlantic salmon with an initial average weight of 160 grams. During the challenge, the fish were kept in a tank supplied with particle filtered and UV treated brackish water (15 ‰ salinity, 12°C) up to 3 weeks post challenge (wpc). The fish were then switched to seawater (34 ‰ salinity, 12°C) for the remaining time of the study. The inoculum, consisting of pelleted blood cells, originated from a HSMI outbreak in 2012 and had undergone one previous passage in experimental fish. The inoculum has previously been described [31 (link)]; it contained high loads of PRV as analyzed by RT-qPCR, and was confirmed negative for infectious pancreatic necrosis virus (IPNV), infectious salmon anemia virus (ISAV), salmonid alphavirus (SAV) and piscine myocarditis virus (PMCV). Prior to inoculation, the blood pellet was diluted 1:1 in PBS.
A cohabitation challenge was run with 75 shedder fish injected intraperitoneally with 0.1 mL inoculum, marked by shortening of the adipose fin and placed in a tank containing 75 naïve fish (cohabitants). To estimate the peak of infection, heparinized blood was taken from the caudal vein of five cohabitant fish weekly, from 3 wpc to 6 wpc. At peak of infection, remaining fish were sampled on three subsequent occasions; 7 wpc (n = 16), 7 wpc + 2 days (n = 16) and 8 wpc (n = 24). At each sampling, two non-infected fish of the same population kept in a separate tank served as negative controls. In addition, blood samples were collected from five fish before initiation of the experiment (0 wpc).
The heparinized blood was immediately analyzed for PRV by flow cytometry, as described below. The blood was then centrifuged at 3000 × g for 5 min at 4°C, separating plasma and blood cells. Both were analyzed for PRV by RT-qPCR and the remaining samples were stored for PRV purification (details described below).
A cohabitation challenge was run with 75 shedder fish injected intraperitoneally with 0.1 mL inoculum, marked by shortening of the adipose fin and placed in a tank containing 75 naïve fish (cohabitants). To estimate the peak of infection, heparinized blood was taken from the caudal vein of five cohabitant fish weekly, from 3 wpc to 6 wpc. At peak of infection, remaining fish were sampled on three subsequent occasions; 7 wpc (n = 16), 7 wpc + 2 days (n = 16) and 8 wpc (n = 24). At each sampling, two non-infected fish of the same population kept in a separate tank served as negative controls. In addition, blood samples were collected from five fish before initiation of the experiment (0 wpc).
The heparinized blood was immediately analyzed for PRV by flow cytometry, as described below. The blood was then centrifuged at 3000 × g for 5 min at 4°C, separating plasma and blood cells. Both were analyzed for PRV by RT-qPCR and the remaining samples were stored for PRV purification (details described below).
Full text: Click here