Comparative Histologic Changes in shrimp Litopenaeus vannamei exposed to attenuated WSSV vaccine produced by Gamma irradiation with unvaccinated shrimps

Abstract

Introduction: Regarding to white spot syndrome extent and threat of shrimp culture,
preventive measures such as efficient vaccine production is necessity. So, this study was
done to evaluate of histologic changes in shrimp Litopenaeus vannamei exposed to
attenuated WSSV vaccine produced with unvaccinated shrimps.
Materials & Methods: 360 shrimp without white spot disease was divided in four groups
of 90th with an average weight of 1.0± 0.1 gr were collected and transferred to the shrimp
research institute. The L. vannamei virus was selected and exposed to doses of 14-15k Gy
per seconds to gamma rays and the inactivated virus was produced as an attenuated
vaccine. The selected shrimps were divided to vaccinated and then encountered to virus
(T1), exclusively vaccinated (T2), positive control (infected with white spot virus) (C+)
and unvaccinated and not encountered with virus as negative control(C-) groups. T1 and
T2 groups were initially vaccinated for 7 days and from eighth day, T1 and C+ groups were
exposed to white spot virus then for 14 days shrimps were kept in separated tanks. Shrimps
were fixed by Davidson solution for histologic study then dehydration, wax infiltration
and impregnation were done by tissue processor and stained by Haematoxylin & Eosin/
phloxine. Histologic changes were seen by optical microscope.
Results: The most inclusion body were seen in gill, hepatopancreas, lymphocytes,
muscular cells.
Conclusion: The attenuated virus with gamma ray seems significantly to reduce the
mortality rate in shrimps which it can be used as an appropriate method to control white
spot disease.