Cyprinivirus

Cyprinivirus is a genus of viruses in the family Alloherpesviridae, order Herpesvirales. Members are large, enveloped DNA viruses that infect freshwater fishes, particularly cyprinids such as common carp and koi. They possess large double‑stranded DNA genomes and replicate in the nuclei of host cells.

The genus includes several cyprinid herpesviruses, notably Cyprinid herpesvirus 1 (CyHV-1, carp pox virus), Cyprinid herpesvirus 2 (CyHV-2, goldfish hematopoietic necrosis virus), and Cyprinid herpesvirus 3 (CyHV-3, koi herpesvirus, KHV). These viruses can cause significant disease in aquaculture and ornamental fish, with species showing varying tissue tropisms and clinical presentations.

Disease in cypriniviruses ranges from localized skin lesions to systemic illness. CyHV-3 is the best known for causing mass mortality in koi and common carp, particularly under warmwater conditions, with symptoms such as lethargy, erratic swimming, gill necrosis, and gill erosion. CyHV-1 causes carp pox, characterized by wart-like skin lesions. Transmission is primarily horizontal, through water and direct contact, and the viruses can persist in aquatic environments and within infected tissues. Stress, temperature changes, and high fish density facilitate outbreaks.

Diagnosis relies on molecular methods, especially PCR detection of viral DNA from gill or tissue samples, complemented by histopathology and virus isolation in cell culture where available. Prevention focuses on biosecurity, surveillance, quarantine of new stock, and disinfection; movement controls help limit spread. Vaccines have been developed for koi herpesvirus in some regions, and vaccination is used as part of disease management in commercial settings. Cyprinivirus remains a major concern in aquaculture and ornamental fish health.