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.
Description:
A Thesis
Submitted to the Faculty of Agriculture,
Sher-e-Bangla Agricultural University, Dhaka,
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
IN
BIOTECHNOLOGY
SEMESTER: JULY-DECEMBER, 2021
