Title : Evaluation of microplastics (MP) as a risk factor for White Spot Syndrome Virus (WSSV) in white leg shrimp (Penaeus vannamei)
Abstract:
Plastic wastes have become a prominent environmental concern in recent years. Unfortunately, a substantial amount of plastic wastes are being discharged into the marine environments, eventually accumulating in aquatic organisms in the form of microplastics (MP). Existing studies have reported detrimental impacts associated with MP exposure to aquatic organisms, such as reduced feed intake, nutrition-related problems, and weakened immune system. White spot syndrome virus (WSSV) is a viral pathogen that poses a significant threat to shrimp, environmental stress factors, such as physical and chemical changes in water, can accelerate viral replication and thus increase infection. This study was conducted under the assumption that MP could be a risk factor for infectious diseases. To investigate the potential role of MP as a risk factor, an experiment was conducted using shrimp as a model organism. Thirty-two experimental shrimp with an average weight of 1.5?±?0.05?g were divided into four groups, each with duplicates. The first group (group 1) was not exposed to either WSSV or MP. The second group (group 2) was exposed solely to MP. The third group (group 3) was exposed only to WSSV, and the fourth group (group 4) was exposed to both WSSV and MP. Group 1 and group 2 were fed specific pathogen-free (SPF) shrimp tissue once, whereas group 3 and group 4 were fed WSSV stock once to induce WSSV infection. Following this, group 1 and group 3 were injected with 50 μL of 1X PBS, both orally and anally, whereas group 2 and group 4 were injected with 50 μL of MP, both orally and anally, for MP exposure. The result showed that group 4 (exposed to both WSSV and MP) experienced mortality within 24 hours of MP exposure, with a 50% accumulative mortality rate at the experience termination day. In contrast, no mortality was observed in group 1, 2, and 3. Histological examination showed that shrimp in group 2, exposed solely to MP, showed collapsed tubule structures, and loss of B-cells (large vacuole in tubule) in hepatopancreas. Additionally, many nuclei showing abnormal shape and slight lysis were observed in muscle fibers. Group 3, exposed only to WSSV, exhibited basophilic inclusion body in hepatopancreas epithelial and gill tissue, along with many abnormally shaped nuclei in muscle fibers. Group 4, exposed to both WSSV and MP, showed basophilic inclusion body and separation of basement membrane in hepatopancreas, along with numerous basophilic inclusion bodies in gill tissue. Also, many abnormal shaped nuclei along with infiltrated and dissolved muscle fibers were observed. In conclusion, this study highlights the increased risk of disease infection that may result from exposure to MPs in shrimp. Furthermore, it suggests that this elevated risk could cause significant economic losses in the aquaculture industry.
