Prevalence of cyprinid herpesvirus-2 in goldfish aquarium shops in Tamil Nadu, India: a case report.

This study reports cyprinid herpesvirus-2 infection in farm-reared goldfish in Tamil Nadu during surveillance between 2022 and 2024. CyHV-2 is a temperature-dependent viral pathogen that causes mortality during temperature fluctuations of 18-24°C (post monsoon). Live goldfish showing hemorrhage, skin ulcers, pale gill color, and high mortality rates were collected from aquarium shops in Kolathur, Chennai District, Tamil Nadu, India. To examine pathogenesis, PCR and RT-PCR assays were performed on disease-suspected samples using primer sets for viral infections, such as CyHV-2, CyHV-3, CEV, VHSV, and SVCV. These results confirmed that the CyHV-2 infection caused mortality. CyHV-2 was confirmed by sequence analysis of the ORF92 of CyHV-2 with the reported CyHV-2 strains worldwide. Sequence analysis results showed 97.1 to 100% similarity with the CyHV-2 sequence reported in GenBank. The snakehead kidney cells (CSK) were susceptible to CyHV-2 and replication was confirmed by virus-specific cytopathic effects, PCR, and bioassays. The CyHV-2 was injected in healthy fish through the IM route using viral inoculum derived from infected fish, and the virus was cultivated in susceptible cell lines. Prominent PCR bands indicated that CyHV-2 demonstrated tissue tropism in all the essential organs. The relative expression level of immune-related genes TLR22, HSP70, IL-1β-1, IL-1β, IFNγ-1, TGF-β, and TNF1 was examined in the kidney and spleen of CyHV-2-infected fish using RT-qPCR. During the early stage of infection (48-72 h post-infection), the expression level of TLR22, HSP70, IL-1β, IL-1β-1, IFNγ-1, and TNF1 was significantly upregulated, whereas they were downregulated at 96 h post-infection onwards. In contrast, the TGF-β gene was consistently downregulated throughout the experimental period.