Oral vaccination trials with crayfish, Procambarus clarkii, to induce resistance to the white spot syndrome virus.

The potential of oral vaccination against white spot syndrome virus (WSSV) in crayfish Procambarus clarkii was investigated. The protective effect of binary ethylenimine (BEI)-inactivated WSSV was tested by oral vaccination, followed by an oral challenge with WSSV. The crayfish fed with feed pellets coated with BEI-inactivated WSSV showed a resistance to WSSV on the seventh day post vaccination (dpv). The relative percentage survival values were 60%, 70% and 75% for the vaccinated once, twice and thrice with inactivated WSSV. Following an intramuscular injection experiment, no mortality was recorded in the inactivated WSSV group and the negative control at 17 days post challenge. The cumulative mortalities in the heated WSSV group and WSSV group were 100%. Shrimp that survived the WSSV challenge on the seventh day after cessation of oral vaccination were positive for the presence of WSSV by a polymerase chain reaction assay specific for WSSV. This result indicated that inactivated WSSV could protect crayfish against WSSV by oral delivery.