Genetic Diversity of Cyprinid Herpesvirus 3 from Different Geographical Locations during 1999–2019 in the United States of America

Abstract

Cyprinid herpesvirus 3, also known as koi herpesvirus (KHV), is an important pathogen in common and koi carp Cyprinus carpio, varieties. Two main genotypes of KHV have been reported worldwide that are associated with Asian and European origins. In the USA, outbreaks of KHV diseases have been reported in different states since the early 1990s; however, the diversity of KHV is unknown. In the current study, 67 DNA samples that were extracted from clinical cases of koi tissues that were submitted for diagnosis during KHV outbreaks from 10 different states in the USA from 1999 to 2019 were used to investigate their genetic diversity. The thymidine kinase gene was amplified, sequenced, and used for phylogenetic analysis. Our results showed that the KHV isolates that were collected from the different states were clustered in the two known KHV genogroups, where 31 isolates belonged to the Asian genotype branch and 36 to the European genotype branch. The spatiotemporal analysis demonstrated fluctuation of KHV genotypes in the USA, as the main KHV genotype that was detected in koi in the USA from 1999 to 2013 was the European genotype, whereas the Asian KHV genotype appeared to emerge in the USA in 2008, increasing in incidence until 2019. The current study provides evidence on the genetic diversity of KHV in the USA. Future studies that evaluate the virulence of these genetically diverse isolates is warranted to obtain a better understanding of the epidemiology of this re‐emerging pathogen. This may provide an improved awareness of the current status of KHV and help to control the disease in the koi population in the USA.

Susceptibility of Pimephales promelas and Carassius auratus to a strain of koi herpesvirus isolated from wild Cyprinus carpio in North America

“…Furthermore, most CyHV-3 genomes available originated from cultured carp and koi and thus, CyHV-3 genomes originating from wild carp are especially limited. The genome sequence of the isolate obtained in this study is of the same lineage (European) as that of CyHV-3 detected in Elysian in 2017 3 , as well as most strains of CyHV-3 originating prior to 1999 when Asian lineage strains began to emerge in the USA 39 . Anthropogenic movement of wild carp in the USA has been under strict regulation since the 1980s and it was well documented that carp was introduced to North America from Europe, much earlier, in the late 1800s 40 .…”

The analysis of a cluster of koi herpesvirus disease outbreaks in intensive carp aquaculture using molecular and conventional epidemiology

“…This again supports the conventional epidemiological data, which failed to link the 2020 outbreaks to the 2018–2019 cases. Duplex and conventional PCR (Bigarré et al, 2009; Shahin et al, 2020) confirmed the Asian origin of the 2020 sample CZ2296 isolated from koi carp, in contrast to all of the other studied isolates assigned to European lineage. The diverging TK sequences of viruses CZ2241 and CZ2300 showed a small but significant rate of mutations for a double‐stranded DNA virus in the relatively short time span of the study (Sanjuán et al, 2010) suggesting a more widespread underlying presence of KHV in Czech aquaculture.…”

“…This again supports the conventional epidemiological data, which failed to link the 2020 outbreaks to the 2018-2019 cases. Duplex and conventional PCR(Bigarré et al, 2009;Shahin et al, 2020) confirmed the Asian origin of the 2020 sample CZ2296 isolated from koi carp, in contrast to all of the other studied isolates assigned to European lineage. The diverging TK sequences of viruses CZ2241 and CZ2300 showed a small but significant rate of mutations for a double-stranded DNA virus in the relatively short time span of the study(Sanjuán et al, 2010) suggesting a more widespread underlying presence of KHV in Czech aquaculture.As only a few outbreaks of KHVD are usually reported in the country per year (European Commission, 2022) the role of inapparent and latent infections cannot be ruled out(Eide et al, 2011) underlining the importance of active surveillance programmes (EU, 2015/1554).5 | CON CLUS IONRoutine carp relocation, shared watercourses and unsanitized fishing equipment have allowed the spread of koi herpes virus with 100% phylogenetic identity to 10 ponds in the Pardubice region in 2018-2019.…”

“…Duplex (Bigarré et al, 2009) and conventional (Shahin et al, 2020) PCR were used to determine the virus lineage. Twelve viruses were of CyHV3-U/ I lineage.…”