Hematology-centered characterization of β-glucan-mediated disease trajectory modulation during rock bream iridovirus (RBIV) infection.

Rock bream iridovirus (RBIV) causes a rapid systemic infection, severe hematological disruption, and high mortality in rock bream (Oplegnathus fasciatus). Although β-glucan is widely used as an immunostimulant in aquaculture, its influence on RBIV disease progression remains poorly understood. Therefore, this study evaluated the effects of different β-glucan administration schedules on survival, viral dissemination, and blood-associated physiological responses during experimental RBIV infection. Among the tested schedules, the 300 μg/fish Pre + Post regimen (-2 and + 2 dpi) provided the greatest survival benefit, reducing cumulative mortality from 100% to 60%, and was selected for further analyses. Compared with virus-only fish, β-glucan treatment improved survival while delaying systemic viral dissemination, reducing viral burden, and attenuating hematological deterioration throughout infection. Attenuation analyses demonstrated stage-dependent protection, with the strongest reductions in leukocyte-associated disturbance occurring during the early phase of infection, whereas preservation of erythrocyte-associated parameters was most evident during the middle phase. In contrast, biochemical responses showed comparatively limited treatment-associated effects. Overall, these findings indicate that β-glucan did not function as a direct antiviral agent but instead modified the trajectory of RBIV disease progression by slowing systemic viral expansion and attenuating hematological deterioration. These results further support the concept that preservation of hematological integrity represents a key component of disease resilience during RBIV infection.