Evaluating of the role of direct fish-to-fish contact on horizontal transmission of Koi herpesvirus

Common carp (Cyprinus carpio) is a widely cultured fish produced for food globally. It was introduced into Australia for aquaculture and carp is now abundant and widespread in many Australian waterways. Reported impacts from carp include reduction in water quality, river bank damage and may contribute to algae blooms. In addition, the increased spread of carp and its impact on freshwater habitat has come at the expense of native fish species and aquatic vegetation. To reduce the carp population and aid native species recovery, the Australian Government is evaluating the release of cyprinid herpesvirus 3 [CyHV-3, also known as koi herpesvirus (KHV)] as a biocontrol agent against invasive carp in Australia. However there are concerns about the safety and efficacy of the use of KHV as a biocontrol agent. Epidemiologic modelling to predict the disease outcomes for carp populations in Australia are important to predict the efficacy of KHV for biocontrol (Durr et al 2019). Key aspects of KHV delivery into a target carp population will be the time of year that infected fish are released and understanding the most significant ways in which the virus is spread between fish. A key for KHV models is to determine if direct transmission (ie requiring direct fish-to-fish contact) is more important than indirect transmission (whereby naïve carp can be infected by KHV shed into the water). This will determine the relative efficacy of KHV biocontrol during carp aggregation. This investment will use a laboratory infection model to evaluate KHV replication and shedding in injected carp. Further, the relative importance of direct and indirect transmission of KHV will be compared. This will inform epidemiologic models to improve predictions and management of a controlled KHV release.