Figure 8

Schematic representation of the putative pathogenesis of PRV-1b and PRV-3a infection and the association with clinical disease characterized by cardiomyopathy, hemolytic anemia, and prehepatic jaundice in coho salmon farmed in Chile. A Infection and replication of both PRV subgroups would initially occur in at least two compartments: (1) erythrocytes, and (2) cardiomyocytes of the spongy myocardium. Reduced erythrocytes count and hematocrit (anemia) added to low blood hemoglobin concentration and maintained high plasma LDH and ALP concentrations in some fish (hemolytic anemia). Most fish showed normochromic-normochromic anemia and presence of reticulocytes (regenerative anemia) as seen in typical hemolytic anemia. The concentration of direct or conjugated bilirubin remained at basal levels, which would confirm the accumulation of indirect or unconjugated bilirubin (pre-hepatic jaundice). B Time course of PRV-1b and PRV-3a infection in coho salmon farmed at farm 1 and farm 2, respectively. Initial viral loads were low and there were no clinical signs of disease or macroscopic pathological lesions (clinically asymptomatic carriers). When the viral load increased at the intermediate stage, a low frequency of fish with a slight drop in blood hemoglobin concentration was recorded, probably related to the onset of apoptosis and rupture of erythrocytes (infected with PRV). Remarkably, despite the significant reduction of viral load in tissues, the frequency of macroscopic lesions and mortality increased during the final stage of the study. Microscopical changes such as splenic congestion of moderate extent with multiple hemosiderin deposits, moderate to severe diffuse hepatic atrophy and vacuolar depletion in the enterocytes of the hindgut appeared, which together indicate a systemic process tending to chronicity. Leukopenia and lymphopenia were observed, but still with the presence of reactive lymphocytes, all probably related to the chronic viral infection. Total hyperbilirubinemia remained the most frequent and important change in the blood biochemical profile.