Differences in CyHV-3 infection and infectivity among common carp and Asian carp species

Common carp ( Cyprinus carpio ) is a very widely distributed fish species, both in aquaculture and in the wild. Outbreaks of the disease caused by Cyvirus cyprinidallo 3 have been significantly damaging aquaculture production and also impacted wild populations. Common carp is the major host of this virus, but virus presence in other cyprinids was also reported. Common carp and related cyprinids are found together in nature and often farmed together. We aimed to study host-pathogen interactions for cyprinids, with respect to disease resistance and virus transmission. We tested if Asian carps, including grass carp ( Ctenopharyngodon idella ), black carp ( Mylopharyngodon piceus ), silver carp ( Hypophthalmichthys molitrix ), and goldfish ( Carassius auratus ) could be infected upon cohabitation with common carp. Unlike in common carp, little mortality was observed and only a minority of these other cyprinids were virus positive by PCR, indicating that these cyprinids are mostly infection resistant. Overriding this infection barrier by virus injection resulted in significant viral loads and viral replication in the spleen of all tested cyprinid species. However, unlike common carp, other cyprinids cleared the virus faster and suffered no mortality, implying that these cyprinids are also disease resistant. Lastly, cohabitation of common carp with virus-injected cyprinids indicated that these fishes are much less infective than common carp are. Our results demonstrate that Asian carps are less infected, less susceptible, and less infective than common carp may be. Therefore, these cyprinids should be categorized as inefficient carrier hosts. The co-existence of multiple cyprinid species might only slightly increase risks of disease outbreak in common carp aquaculture.