Use of a methanolic olive leaf extract (Olea europaea) against white spot virus syndrome in Penaeus vannamei: Comparing the biochemical, hematological and immunological changes

Abstract

The main goal of this study was to investigate the biochemical, hematological, and immunological impacts of olive (Olea europaea) leaf extract (OLE) in Penaeus vannamei experimentally infected by white spot syndrome virus (WSSV). A total of 160 juvenile whiteleg shrimp (11.1 ± 0.2 g), obtained from a private sector in Hormozgan Province (Iran), were kept for two weeks to acclimatize to conditions in the facility aquarium. The health status of the shrimp was assured by random sampling before experiment action; PCR testing confirmed the absence of common shrimp diseases. Three groups, each consisting of 20 shrimp fed with three different doses of OLE (50, 100, 200 mg/kg of the shrimp biomass), and a positive control group (not feeding with OLE), were all orally subjected to a virus challenge two weeks later. For comparison, three negative control groups with 20 shrimp were fed three different doses of OLE, and another group was fed with a diet lacking OLE. The PCR test confirmed the presence of the WSS virus in the treatment and positive control groups, while the negative control groups did not show any infections. The hemolymph of shrimp was taken on days 1, 8, and 22 from all groups after challenge for evaluation of hemolymph total protein, glucose, oxyhemocyanin (OxH), superoxide dismutase (SOD), phenoloxidase (PO) activity, coagulation time, and total hemocyte count (THC). Results showed that shrimp survival significantly increased up to 65% when fed with high doses of OLE for seven days. The maximum hemolymph total protein and glucose levels significantly belonged to the treatment that was challenged by WSSV without receiving OLE. The present findings indicate WSS infection caused a significant decrease in OxH level compared to that of the control groups. Therapeutic feeding with OLE could significantly decrease the SOD and PO activities, and the hemolymph clotting time. We did not see no remarckable effects of OLE on the total hemocyte count. In conclusion, the various indices studied in this research showed that the olive leaf extract would be useful in the control and prevention of white spot syndrome.