Mourilyan virus pathogenicity in kuruma shrimp (Penaeus japonicus)

The bunyavirus Mourilyan virus (MoV) occurs commonly in Black tiger (Penaeus monodon) and kuruma shrimp (Penaeus japonicus) farmed in eastern Australia. There is circumstantial evidence of MoV causing mortalities among P. japonicus moved from farm ponds to tanks for rearing as broodstock. To directly assess its pathogenic potential, independent cohorts of pond- (n = 24) or tank-reared juvenile (n = 21) P. japonicus were challenged intramuscularly with a cephalothorax tissue homogenate of P. monodon containing high loads of MoV (1.48 ± 0.28 × 10⁸ MoV RNA copies/µg total RNA). In each trial, mortalities accumulated gradually among the saline-injected controls. Mortality onset occurred 12-14 days earlier in the pond-reared shrimp, possibly due to them possessing low-level pre-existing MoV infections. Despite the time to onset of mortality differing, Kaplan-Meier survival analyses confirmed mortality rates to be significantly higher in both the pond- (p = .017) and tank-reared shrimp (p = .031) challenged with MoV. RT-qPCR data on shrimp sampled progressively over each trial showed high loads of MoV to establish following challenge and discounted GAV and other endemic viruses from contributing to mortality. Together, the data show that acute MoV infection can adversely compromise the survival of juvenile P. japonicus.