White spot disease has caused significant economic losses in the shrimp farming industry of Bangladesh over the last two decades. The responsible virus, WSSV, may show severe disease with significant mortality depending on farm management and environmental and seasonal changes. Data on farm management and environmental parameters were collected from the southwest region of Bangladesh in 2018, and WSSV infection was confirmed by the species-specific gene VP28 using conventional PCR, real-time PCR and sequencing. Through bivariate analysis, nine significant risk factors for WSD were identified, viz. farm age, presence of nursery pond, reservoir of PL, weed in farm area, control of weed, stocking density, stocking frequency, ammonia and oxygen concentration. This study detected 46 WSSV-infected shrimp farms by conventional PCR, whereas real-time PCR identified 47 WSSV-positive out of 49 farms. WSSV prevalence was highest in the Khulna region, with 100% positivity in all seasons. WSSV loads ranged from 5.62 × 109 to 2.01 × 1015 copies/g of shrimp tissue. The VP28 gene sequence confirmed that 15 representative samples were 100% identical to the 2018 WSSV strain of India. The relationships among risk factors, prevalence and severity of disease, and origin of WSSV strains could be impactful for WSD management.
Keywords: Real-time PCR; Risk factors; Shrimp; VP28 gene; WSSV.
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