It is everywhere—A survey on the presence of carp edema virus in carp populations in Germany

Abstract

Carp edema virus (CEV) is the causative agent of koi sleepy disease (KSD), a serious gill disease affecting common carp, Cyprinus carpio, and its ornamental variety, koi. After recent detections of the virus in various countries around the world, KSD has emerged as a new global disease in carp. However, the prevalence of the infection in carp populations in a given geographical region has not been studied thoroughly. The present communication reports an investigation into the presence of CEV in carp and koi populations in Germany. For this purpose, gill samples collected from carp and koi populations suffering from gill diseases or collected for a routine examination of their health status were tested for the presence of CEV by PCR. In total, 651 fish samples from 401 carp or koi cases were examined in 2015 and 2016, additional 118 samples from previous studies were included in the examination. CEV was detected in archive samples from carp dating back to 2007, and in koi samples dating back to 2009. From 2015 to 2016, CEV was detected in 69% of cases from carp populations examined from the main carp‐producing areas in Germany, and in 41% of the examined cases from koi populations from all over Germany. Clinical KSD occurred mainly from April to June in carp populations at water temperatures ranging from 8 to 12°C and in koi populations at water temperatures ranging from 18 to 22°C. Most fish from clinically affected carp or koi populations harboured high virus loads of above 10,000 copies of CEV‐specific DNA per 250 ng DNA, while gills from fish of other fish species from the ponds, including goldfish, grass carp and European perch were found CEV negative or harboured a low virus load. A phylogenetic analysis revealed the presence of multiple CEV variants from genogroup I in carp and genogroup II in koi populations in Germany. Genetically identical genogroup I isolates were detected in carp from different geographical locations in Germany and in other European carp populations. Some German genogroup II variants were identical to variants previously recorded from koi in Asian and other European countries. The data presented here show that CEV is highly prevalent in German common carp and koi populations and implies the spreading of this virus by intense trading of common carp and koi without necessary risk mitigating measures. As infections with this virus may induce serious disease, CEV diagnostic should be included in health surveillance and disease monitoring programmes.

Gill disorders in fish: Lessons from poxvirus infections

“…Subsequent cases of CEV infection were documented in populations of koi as well as common carp in the United States (1996, 2005 and 2010) and in Europe: Belgium, Germany (2009), England (2011), Austria, the Czech Republic, France, the Netherlands and Poland (2014) 77 . There are currently two main distinct genogroups of CEV with a different geographical distribution 78 . The European genogroup I is found mainly in farmed or wild common carp in Europe and the USA, while the Asian genogroup II is mainly found in common carp in Asia and is now distributed worldwide in koi due to the global ornamental fish trade 79 .…”

“…The European genogroup I is found mainly in farmed or wild common carp in Europe and the USA, while the Asian genogroup II is mainly found in common carp in Asia and is now distributed worldwide in koi due to the global ornamental fish trade 79 . A recent survey showed that both genogroups of the virus are widespread and responsible for multiple outbreaks in cultured and natural populations of common and koi carp worldwide every year 78 . Under experimental conditions, the onset of severe clinical signs leading to mortality occurs within the first week of infection with CEV 31 .…”

“…77 There are currently two main distinct genogroups of CEV with a different geographical distribution. 78 The European genogroup I is found mainly in farmed or wild common carp in Europe and the USA, while the Asian genogroup II is mainly found in common carp in Asia and is now distributed worldwide in koi due to the global ornamental fish trade. 79 A recent survey showed that both genogroups of the virus are widespread and responsible for multiple outbreaks in cultured and natural populations of common and koi carp worldwide every year.…”

Workshop report: Diseases of ornamental and laboratory fishes

“…For example, testing of several shipments of koi, which were sent to German retailers from Japan, showed that asymptomatic fish were repeatedly found positive for the virus (Adamek et al 2016). Furthermore, observation of fish and sequencing of the virus from some fish farmers in Germany showed that over the period of 2014-2021 repeating outbreaks of KSD were caused by the same virus variants, which could hint that the virus persisted in the population (Adamek et al 2021). However, the experimental infections did not confirm a transfer of the virus from survivors of the CEV infections (Adamek et al 2017).…”

The influence of viral infection on cell line characteristics: Lessons learned from working with new cell lines from common carp

“…Therefore, the disease associated with a CEV-infection is referred to as Koi Sleepy Disease (KSD). Infections with CEV were found to be widespread in the carp population in European aquaculture (Adamek, Heling, et al, 2022). Even though a limited replication of CEV was observed in explant cultures of carp gills (Adamek et al, 2017), an in vitro cultivation of this virus is not yet possible.…”