The efficacy of recombinant vaccines against white spot syndrome virus in Procambarus clarkii.

The effectiveness of oral, mock-, and immersion vaccination was investigated against white spot syndrome virus (WSSV) in crayfish. The most exposed WSSV envelope proteins VP19 and VP28 were used in different compositions and with different modes of applications. In experiment 1 crayfish were fed recombinant protein coated food pellets for 25 days, in experiment 2 the purified proteins were directly injected to them followed by one booster dose on 5th day and in experiment 3 the crayfish were left immersed in vaccines for 7 h. Experimental crayfish were challenged on 3rd and 21st days after last vaccination. The overall result showed that VP28 group has lowest cumulative mortality percentage accounting 39.6% at 3rd day and 39.83% at 21st day when injected and it was 43.2% and 49% when fed orally and 46.3% and 46.5% when immersed at 3rd and 21st days, respectively (p<0.05). In VP19 and VP28 (50:50) mixture, mock vaccination showed better performance (36.5%) over immersion (53%) and oral vaccination (53.2%) when challenged on 3rd day and mock vaccination (36.50%) followed by oral (51%) and immersion vaccination (56.5%) on 21st day as well. The VP19 recombinant mock vaccination group performed better (52.91% of 3rd day and 56.46% of 21st day) than oral (76% of 3rd day and 82% of 21st day) and immersion (83% of 3rd day and 86.3% of 21st day) vaccine groups. All the experimental groups except VP19 were significantly different (p<0.05) from the control groups. A positive cumulative effect was observed when VP28 was mixed with VP19 in equal proportion in all the experimental trials, which shows the effectiveness of VP19 as a vaccine component too. In the present trial on the basis of cumulative mortality percentage it is found that mock-vaccination group is more effective than the oral vaccination and immersion vaccination. It also suggests that specific memory exists in crayfish and the effects of VP28 are significant. The effect of VP19 along with VP28 has also shown significant effect against WSSV.