Long-term detection of cyprinid herpesvirus 1 genome and tumorous transcriptome in common carp (Cyprinus carpio) infected with the virus

Abstract

Cyprinid herpesvirus 1 (CyHV-1) disease induced by CyHV-1 (Cyvirus cyprinidallo1) causes mortality in common carp (Cyprinus carpio) and formation of tumors on the skin of infection-tolerant fish. Similar to other viruses in the Orthoherpesviridae family, CyHV-1 appears to establish latent infections. However, information regarding the mechanisms of genetic conservation for a prolonged period and tumorigenesis by CyHV-1 is limited. Here, we aimed to reveal i) potential tissues where the virus establishes persistent infection, and ii) the transcriptome characteristics of tumors formed in common carp infected with CyHV-1. In fish experimentally infected with the virus, the presence of the viral genome was observed in kidney, spleen, and gill tissue at 300 days post injection, a long time after the injection. This result suggests that CyHV-1 may utilize one or more of these tissues for its persistency. In fish naturally infected with CyHV-1 at a fish farm, transcriptome analysis showed substantial quantities of viral transcripts in tumor tissue. Of the 5 most abundant viral transcripts expressed in the tumor tissue, 4 transcripts (ORF81, ORF78, ORF31, and ORF72) are believed to encode virion proteins. This indicates the virus was active in the tumor tissue. Pathways altered in tumor tissue included those related to viral infection or cancer cells, suggesting that viral infection and tumor formation affect the metabolism of the host. This study is the first to report the likely persistent tissues of CyHV-1 and molecular mechanisms involved in tumor formation caused by an oncogenic virus in fish. These findings contribute to the development of quarantine measures for CyHV-1 and provide insights into the oncogenic mechanism of fish viruses.