Abstract
Cyprinid herpesvirus 2 (CyHV-2), a member of the Alloherpesviridae family belonging to the genus Cyprinivirus, is a fatal contagious aquatic pathogen that affects goldfish (Carassius auratus) and crucian carp (Carassius carassius). Although crucian carp and goldfish belong to the genus Carassius, it is unclear whether they are susceptible to the same CyHV-2 isolate. In addition, the origin of the crucian carp-derived CyHV-2 virus isolate remains unclear. CyHV-2 SH01 was isolated during herpesviral hematopoietic necrosis disease (HVHN) outbreaks in crucian carp at a local fish farm near Shanghai. CyHV-2 SH01 was confirmed by PCR and Western blot analysis of kidney, spleen, muscle, and blood tissue from the diseased crucian carp. Moreover, histopathological and ultra-pathological analyses revealed pathological changes characteristic of CyHV-2 SH01 infection in the tissues of the diseased crucian carp. In the present study, goldfish and crucian carp were challenged with CyHV-2 SH01 to elucidate viral virulence. We found that CyHV-2 SH01 could cause rapid and fatal disease progression in goldfish and crucian carp 24 h post-injection at 28 °C. Experimental infection of goldfish by injection indicated that the average virus titer in the kidney of the goldfish was 103.47 to 103.59 copies/mg. In addition, tissues exhibited the most prominent histopathological changes (cellular wrinkling and shrinkage, cytoplasmic vacuolation, fusion of the gill lamellae, and hepatic congestion) in CyHV-2 SH01-infected goldfish and crucian carp. Thus, crucian carp and goldfish showed a high sensitivity, with typical symptoms, to HVHN disease caused by CyHV-2 SH01.
Highlights
The order Herpesvirales includes the families Alloherpesviridae, Malacoherpesviridae, and Herpesviridae, which comprise enveloped DNA viruses
DNA extracted from purified cyprinid herpesvirus 2 (CyHV-2) particles was sequenced, and CyHV-2 SH01 genome sequencing was commercially performed by the NextOmics company (Wuhan, China)
A phylogenetic tree was constructed based on the sequences derived from helicase gene Polymerase Chain Reaction (PCR) products
Summary
The order Herpesvirales includes the families Alloherpesviridae, Malacoherpesviridae, and Herpesviridae, which comprise enveloped DNA viruses. CyHV-2 has a narrow host range and is highly virulent; it has spread to the main areas of crucian carp culture worldwide, and especially in China. Goldfish are cultured as an ornamental pet [12] and were derived from the Prussian carp by artificial selection. Around the year 2010, CyHV-2 infection in the silver crucian carp (Carassius auratus gibelio) instead of the usual host of the goldfish was reported for the very first time [19]. The disease in crucian carp has spread rapidly in many areas, including Hungary, Czechia, Italy, and China [19,20,21,22]. CyHV-2 infection was responsible for considerable economic losses in crucian carp farming, especially in China. We determined whether goldfish were susceptible to CyHV-2 SH01 isolated from crucian carp
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