MOLECULAR AND HISTOPATHOLOGICAL STUDIES OF WHITE SPOT SYNDROME VIRUS INFECTION IN TIGER SHRIMP (Penaeus monodon)

Abstract

Since the 1980s, shrimp farming has been rapidly expanded and has become the third largest export earnings source, contributing about 3.57% to national GDP of Bangladesh. Now this sector facing a serious problem with a disease named White Spot Disease (WSD) caused by dreadful White Spot Syndrome Virus (WSSV), which leads to 100% mortality in the shrimp farm within 3-5 days. This study showed PCR detection and prevalence rate of WSSV infection in Penaeus monodon and further confirmed by histopathological study to observe the pathological changes in the tissue. The prevalence of this virus has been studied in six selected farms located in the Bagerhat and Satkhira districts of Bangladesh. Both one-step and two-step PCR were used to detect using two pairs of primers, namely, 146F1/146R1 and 146F2/146R2, amplifying the 1447 bp and 941 bp fragments, respectively. Out of 36 randomly selected shrimp samples, 25 samples were WSSV-positive other 11 samples were negative by one-Step PCR. The negative eleven samples were further subjected to two- step PCR and resulted only 3 samples being negative. The prevalence rates of WSSV infection were 83.33% and 55.56% in Satkhira and Bagerhat district, respectively, confirmed by one-step PCR and the prevalence rate of WSSV infection was 83.33% and 100% in Satkhira and Bagerhat district, respectively, confirmed by two-step PCR. However, the overall prevalence rate increased from one-step to two-step PCR from 69.44% to 91.67%. Between two methods two-step PCR was more efficient than one-step PCR. The shrimp specimens showing clinical signs of WSSV were positive by both one-step and twostep PCR. Some of the apparently healthy samples were also found to be positive for

WSSV by two-step PCR. Histopathological studies of hepatopancreas of two-step PCR

confirmed WSSV-positive samples resulted in degenerated tubule lumen, degenerated

and

sloughing hepatopancreas with necrosis and infected muscle tissue resulting in fragmentation and separation of muscle fibers. Furthermore, it is suggested that more molecular studies about WSSV and disease management is required to increase the shrimp production in Bangladesh.