Carp Edema Virus (CEV) is a double-stranded deoxyribovirus belonging to the Poxviridae family. It is recognized as the causative agent of Koi Sleepy Disease (KSD) in common carp ( Cyprinus carpio) and koi carp ( C. carpio var. koi) . KSD exhibits clinically with abdominal edema and severe branchial damage and can lead to high mortality rates in infected populations. Although the species showing clinical signs are mainly carp and koi carp, a recent study has shown the presence under experimental conditions of the viral nucleic acid in other cyprinid species, specifically in bleak (Alburnus alburnus), crucian carp ( Carassius carassius), Prussian carp (Carassius gibelio), roach (Rutilus rutilus ) and tench (Tinca tinca) . Our study aims to investigate the presence of CEV in cyprinids in natural basins or kept in environments with positive carp.
The monitoring was conducted in the period 2019-2021, in which 360 cyprinids belonging to 16 different species were analyzed. The analyzed cyprinids were sampled in natural environments (209 fish, 58,06%) or in anthropic environment in case of CEV outbreaks in carp (151, 41,94%) . The subjects sampled were asymptomatic, with the exception of the koi carp analyzed to confirm the outbreaks on the farms. A portion of the gill was used to search for viral DNA following nucleic acid extraction with commercial kits based on silica columns. Therefore, a nested PCR was performed to search for the CEV, based on the work of Matras et al. (2017). The internal primers (CEV-For-B int; CEV-Rev-J int) were also used for Sanger sequencing as further confirmation of the result obtained in PCR.
CEV was found in 24 fish (24/360, p=6,67%) , respectively 20 koi carp, 2 tench, 1 chub (Squalius cephalus) and 1 crucian carp . Koi carp exhibited the typical symptoms of KSD, while other species showed no lesions or atypical behavior. All positive cyprinids came from farms and ponds with positive koi carp, with the exception of the chub which was sampled in the natural enviroment . Sanger sequencing confirmed the PCR results.
Our data confirm the literature regarding the potential role of CEV reservoirs in cyprinids other than carp. Often these fish are in direct contact with symptomatic hosts, as evidenced also by our data: in fact, 22 positives out of 24 are represented by symptomatic koi carp or cyprinids raised in the same environment. Regarding the other positivity, one tench was positive in farm conditions, but had no contact with symptomatic carp . Instead, the chub was sampled in a natural environment, highlighting how the virus can circulate even in natural conditions. Future studies will be needed to implement the available data; in particular, sequencing and phylogenetic analysis of CEV positive samples will be necessary to understand the genogroups circulating on our territory
Matras, M.; Borzym , E.; Stone, D.; Way, K.; Stachnik, M.; Maj-Paluch , J.; Palusi ´nska, M.; Reichert, M. J. Fish Dis. 2017, 40, 319–325