Identification of new genogroups in Austrian carp edema virus isolates

Description, molecular identification and pathological lesions of Huffmanela persica sp. nov. (Nematoda: Trichosomoididae: Huffmanelinae) from the daggertooth pike conger Muraenesox cinereus

BACKGROUND

The genus Huffmanela Moravec, 1987 (Nematoda, Trichosomoididae, Huffmanelinae), represents a group of nematodes that infect both marine and freshwater fish, and the main gross feature of infection with different species of the genus is the presence of noticeable dark spots or tracks within the parasitized tissues. The purpose of this study was to describe morphologically and morphometrically the eggs of a new marine species of Huffmanela (Huffmanela persica sp. nov.), which was found in the form of black spots in the ovary and the tunica serosa of the stomach of the daggertooth pike conger (Muraenesox cinereus). The new species differs from Huffmanela hamo, another species reported from musculature of this host in Japan, in egg metrics, eggshell features and targeted organ. Molecular identification and pathological examination of the lesions caused by the new species are also reported.

METHODS

Nematode eggs with varying degrees of development were separated from the infected tissues (ovary and tunica serosa of stomach) and investigated using light and scanning electron microscopy. Different species-specific markers (small subunit ribosomal DNA, 18S; large subunit ribosomal DNA, 28S; internal transcribed spacer, ITS) were used for molecular identification and phylogenetic study of the new species. Infected tissues were fixed in buffered formalin for pathological investigations.

RESULTS

The fully developed eggs of H. persica sp. nov. are distinguished from those previously described from this host on the basis of their measurements (size, 54-68 × 31-43 µm; polar plugs, 6.4-9.7 × 8.4-12 µm; shell thickness, 3.5-6.1 µm) and a delicate but ornate uterine layer (UL) covering the entire eggshell including the polar plugs. Histopathological examination revealed a fibro-granulomatous inflammation in the ovary and the serosal layer of the stomach of infected fish. Maximum-likelihood (ML) phylogenetic analysis recovered a sister relationship between the new species of marine origin and Huffmanela species previously collected from freshwater hosts.

CONCLUSIONS

The present study is the first to report the molecular characterization and phylogenetic position of a teleost-associated marine species of the genus Huffmanela. A comprehensive list of nominal and innominate populations of Huffmanela is also provided.

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

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.

Complete Genome Sequence of Carp Edema Virus Isolated from Koi Carp

Carp edema virus disease (CEVD), or koi sleepy disease, is caused by CEV. Here, we report the complete genome sequence of CEV strain FTI2020, isolated from koi carp. This sequence information has great potential for improving our understanding of the genetic characteristics of this piscine poxvirus.

Carp edema virus disease (CEVD), or koi sleepy disease, is caused by CEV. Here, we report the complete genome sequence of CEV strain FTI2020, isolated from koi carp. This sequence information has great potential for improving our understanding of the genetic characteristics of this piscine poxvirus.

Carp edema virus and immune response in carp (Cyprinus carpio): Current knowledge

The importance of world aquaculture production grows annually together with the increasing need to feed the global human population. Common carp (Cyprinus carpio) is one of the most important freshwater fish in global aquaculture. Unfortunately, carp production is affected by numerous diseases of which viral diseases are the most serious. Koi herpesvirus disease (KHVD), spring viraemia of carp (SVC), and during the last decades also koi sleepy disease (KSD) are currently the most harmful viral diseases of common carp. This review summarizes current knowledge about carp edema virus (CEV), aetiological agent causing KSD, and about the disease itself. Furthermore, the article is focused on summarizing the available information about the antiviral immune response of common carp, like production of class I interferons (IFNs), activation of cytotoxic cells, and production of antibodies by B cells focusing on anti-CEV immunity.

Koi herpesvirus disease outbreak: Input for the implementation of a surveillance program in South Tyrol - Italy

A severe episode of high and abnormal mortality was observed in the population of Cyprinus carpio of Lake Caldaro (South Tyrol, Italy) in summer 2016. The diagnostic investigation carried out led to the identification of Koi Herpesvirus (KHV) as the etiologic agent. Following this disease outbreak and its socio-economic consequences, the local authorities, in agreement with the local Fishing Association, decided to implement a surveillance program for the achievement of KHV-free health status (Category I) in the Province, in accordance to the Implementing Decision (EU) 2015/1554. The selected area was a defined geographical compartment (the Monticolo lakes compartment, South Tyrol, Italy), which is located near Lake Caldaro, where the Koi Herpesvirus disease (KHVD) outbreak had occurred. This area is of particular interest because it supplies other water bodies with juvenile C. carpio individuals; with the achievement of a KHV-free health status, South Tyrol could possibly become independent in the breeding of this fish species. Suitable samples were collected and processed during a two-year period in order to detect the presence/absence of KHV. The same samples were tested for other viruses that can affect carp, namely spring viraemia of carp (SVCV) and carp edema virus (CEV). According to the results, the authors conclude that the Monticolo lakes area should be classified as KHV-free, as no sample has tested positively for the presence of this specific virus (KHV).

Koi herpesvirus and carp edema virus threaten common carp aquaculture in Croatia

Common carp (Cyprinus carpio) is a very important fish species for warm-water aquaculture in Croatia. All Croatian carp farms are subjected to a surveillance programme for the presence of koi herpesvirus (KHV), causing a deadly disease called koi herpesvirus disease (KHVD). However, there is no surveillance for other viral pathogens of importance like carp edema virus (CEV), a causative agent of koi sleepy disease (KSD). During regular testing within the KHVD surveillance programme, we tested samples for CEV simultaneously. The screening indicated possible outbreaks of KHVD and KSD. During 2016, KHVD broke out in an isolated area and soon thereafter a KHV eradication programme was successfully performed. However, during 2018 and 2019, two additional mortality events occurred in lakes in the southern part of Croatia during the spring. Samples from both events tested positive for CEV. An epidemiological investigation confirmed the introduction of infected carps from an infected farm to one of the lakes. To prevent the spreading of CEV into open waters, it is of utmost importance to introduce CEV testing before fish movement or to perform regular testing of all carp farms in the country to determine CEV prevalence for the purpose of implementation of control measures.