White spot syndrome virus (WSSV) in cultured juvenile blue crabs Callinectes sapidus: oral versus injection exposure, and feeding frequency effects

The efficacy of oral versus injection exposure and the effect of feeding frequency on the transmission of white spot syndrome virus (WSSV) in cultured juvenile blue crabs Callinectes sapidus were investigated. Crabs in Group 1 (G-1, n = 48) were exposed once orally to 100 mg of WSSV-infected shrimp tissue mg(-1) of body weight (BW). The oral inoculum contained 2.6 x 10(9) WSSV genome copies mg(-1) tissue. Group 2 (G-2, n = 46) received the same dosage once weekly for 5 wk. Group 3 (G-3, n = 12) was injected with 0.01 ml (2.6 x 10(7) genome copies 0.01 ml(-1)) WSSV inoculum g(-1) BW. Group 4 (G-4, n = 12) was injected with 0.01 ml WSSV-negative shrimp serum and saline mixture g(-1) BW. Dead and moribund animals were frozen at -80 degrees C. After 37 d, all remaining crabs were frozen. Genomic DNA from gill tissue was evaluated for the presence and quantity of WSSV using TaqMan real-time PCR. All G-3 animals died and tested positive. No G-4 animals died or tested positive. In the fed groups, WSSV prevalence was approximately 16%, but viral load was higher and survival was lower in G-2 compared to G-1. Injected animals carried a higher viral load than fed animals, and dead animals had higher viral loads than live animals. Blue crab juveniles are susceptible to WSSV, but oral exposure does not efficiently transmit WSSV in juvenile blue crabs. Some animals can die from WSSV if repeatedly exposed.