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Cyvirus cyprinidallo2
Cyvirus cyprinidallo2, also known as Cyprinid herpesvirus 2 (CyHV-2) is a species of virus in the genus Cyprinivirus, family Alloherpesviridae, and order Herpesvirales.[1] CyHV2 can also be classified as herpesviral hematopoietic necrosis virus (HVHN) and infects goldfish (Carassius auratus) of all ages.[2][3] It can also infect the closely related species, Prussian Carp (C. gibelio) however koi and goldfish hybrids cannot be infected by CyHV2.[2] Outbreaks have been reported in both cultured and wild populations, and are highly lethal.[2] BackgroundJung and Miyazaki (1995) were the first to describe CyHV2 in Japan.[2][4] This was achieved via isolation from moribund goldfish after the epizootic disease was observed in 1992 and 1993.[4] Culture of HVHN was unsuccessful until 2007.[5] GenomeWhole genome sequencing revealed that the CyHV2 genome is 290,304 bp in size.[3] This number may be variable due to tandem reiterations.[3] Heterogeneous genome size is often observed in other species of herpesviruses.[3] These short yet complex tandem reiterations are most often seen in the terminal direct repeats; the most prevalent being the telomere-like repeats located towards the genome ends.[3] In comparison to the other viruses, the CyHV2 genome is the most complex in terms of the unique regions plus one copy of terminal direct repeats.[3] HVHN has approximately 154 open reading frames (ORFs) and splicing between protein-coding regions affects 9 of these ORFs.[3] Five gene families have been identified. This included multiple genes from TNFR, ORF2, ORF25, RING, and ORF153, as well as ORF22, which is present as a family of two.[3] PathologyExternal symptoms of fish impacted with CyHV2 typically show pale patches localized at the gills but do not exhibit lesions.[2][5] Fish with this infection also appeared to be lethargic, anorexic, and exhibited a loss of appetite.[2][5] CyHV2 is more often characterized by internal symptoms such as an enlarged kidney and spleen, as well as pallor of the kidney.[2] Histopathology of infected goldfish has revealed tissue death in the hematopoietic tissues in both the kidney and the splenic pulp.[2] Necrosis was also observed in the pancreas.[2][4] Smaller, more scattered tissue death and swelling was also observed in the lamina propria as well as the submucosa of the intestine.[2][4] At this time, disease prevention is mainly achieved by avoidance.[2] A formalin-inactivated vaccine developed in 2015 was effective against goldfish infected with HVHN, however, as of now, there is not an established timeline that discusses the duration of protection.[2][6] References
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