Penaeus vannamei is the main farmed shrimp species worldwide, and its cultivation represents the largest non-oil economic sector in Ecuador. However, white spot syndrome virus (WSSV) poses a major threat to its sustainability. P. vannamei larvae are susceptible to WSSV infection via both vertical and horizontal transmission. To reduce the incidence of WSSV in postlarvae (PLs), a bioassay was conducted by exposing WSSV- and WSD-negative PL25 shrimp to two factors, water temperature (24 °C and 31 °C) and immune stimulation with β-1,3-glucans (BG), using a 20-day crossover factorial design.
At the end of the bioassay, WSSV-positive shrimp (confirmed by PCR) were found in all treatments, with the highest infection rate (15.15%) observed in shrimp maintained at 24 °C without BG. In contrast, PLs treated with BG at the same temperature showed a markedly lower prevalence (0.76%). Generalized linear model (GLM) analysis revealed that BG significantly reduced WSSD injuries, particularly in combination with 31 °C. In this treatment, histopathological lesions associated with WSD were nearly undetectable (Table 1). Lesions observed in affected shrimp included damage to the antennal gland, gills, and connective tissue (Table 1). In situ hybridization detected viral presence in nervous, epithelial, and connective tissues, even in specimens that tested negative by histology and PCR (Figure 1).
Apoptosis is one of the initial defense mechanisms employed by shrimp to limit WSSV replication. TUNEL assays revealed mild apoptosis in nervous tissues but prominent apoptosis in epithelial cells, often associated with cuticle damage (Figure 1). These findings suggest that WSSV can enter through the epithelial tissue of cephalic appendages and disseminate via nervous and connective tissues. Apoptosis in the epithelium may facilitate viral entry; however, the combination of BG and elevated temperature (31 °C) may offer a protective strategy to minimize tissue damage and slow viral spread in shrimp populations.