Molecular identification of iridoviruses infecting various sturgeon species in Europe

Abstract

Iridoviridae are known to cause disease in sturgeons in North America. Here, histological and molecular methods were used to screen for this family of virus in sturgeons from various European farms with low-to-high morbidity. Some histological samples revealed basophilic cells in the gill and labial epithelia, strongly suggesting the accumulation of iridovirus particles. Newly developed generic PCR tests targeting the major capsid protein (MCP) gene of sturgeon iridoviruses identified in North America, namely the white sturgeon iridovirus and the Namao virus (NV), produced positive signals in most samples from four sturgeon species: Russian (Acipenser gueldenstaedtii), Siberian (A. baerii), Adriatic (A. naccarii) and beluga (Huso huso). The sequences of the PCR products were generally highly similar one another, with nucleotide identities greater than 98%. They were also related to (74-88%), although distinct from, American sturgeon iridoviruses. These European viruses were thus considered variants of a single new virus, provisionally named Acipenser iridovirus-European (AcIV-E). Moreover, three samples infected with AcIV-E showed genetic heterogeneity, with the co-existence of two sequences differing by five nucleotides. One of our European samples carried a virus distinct from AcIV-E, but closely related to NV identified in Canada (95%). This study demonstrates the presence of two distinct sturgeon iridoviruses in Europe: a new genotype AcIV-E and an NV-related virus.

Outbreak of Mortality Associated with Acipenser Iridovirus European (AcIV-E) Detection in Siberian Sturgeon (<em>Acipenser Baerii</em>) Farmed in Sweden

“…Gill epithelial hypertrophy could indicate iridoviral infection, but only one potential iridoviral inclusion body was found in the lip epithelium, and molecular biology analyses confirmed presence of AcIV-E and absence of NNV in the samples tested. Low prevalence of typical iridoviral histological lesions in AcIV-E infected Siberian sturgeon has been already described [3] and thus the histopathology in this case is in line with previous findings.…”

“…The only pathogenic agent found in diseased sturgeon was AcIV-E. AcIV-E has been described in both Siberian and Russian sturgeon [1,3]. In an Italian farm farming both species, higher mortality due to AcIV-E was present in Russian sturgeon compared to Siberian sturgeon -90% vs 50% [1]suggesting a lower susceptibility to the virus in Siberian sturgeon [1,3]. In the case described here, a cumulative mortality of 95% (including the initial 30% mortality around transport) was reached in two months from arrival in the imported batch of juvenile Siberian sturgeon.…”

A survey of bacterial infections in sturgeon farming in Italy

“…Bacterial diseases caused by primary or opportunistic pathogens are mainly due to farm conditions, among which the chief factor is intensive production. in Italy (Bigarré et al, 2017;Ciulli et al, 2016). Furthermore, these opportunistic bacteria are usually not pathogenic but can cause disease in certain stress conditions (Colussi et al, 2005;Kayiş, El, Kangel, & Kurtoğlu, 2017;Noga, 2010;Quaglio et al, 2000;Timur, Akayli, Korun, & Yardimci, 2010).…”

Comparative evaluation of MCP gene in worldwide strains of Megalocytivirus (Iridoviridae family) for early diagnostic marker

“…The identification of viral infections has always been challenging because of variations in phenotypic characteristics caused due to differences in the ecology, environment and host itself (Go, Lancaster, Deece, Dhungyel, & Whittington, ; Go et al., ; Rimmer et al., ; Shinmoto, Taniguchi, Ikawa, Kawai, & Oshima, ; Whittington et al., ; Williams, ). Currently, there are several detection methods available for the proper diagnostic and identification for viruses (Bigarre et al., ; Boonham et al., ; Go et al., ; Hu et al., ; Whittington et al., ; Xu, Wang, Li, & Yang, ). These detection methodologies vary from biochemical, structural and molecular to immunological methods.…”

“…Various important criteria have been considered for confirming diseases in hosts. Several methods including (i) characteristic iridescent signs of infection (epidermis and fat body); (ii) structural observation using electron microscopy (EM) in the cell cytoplasm (icosahedral particles, internal lipid membrane, ultrastructure, replication and cellular pathology); (iii) genomic DNA analysis; (iv) immunological assays; and (v) molecular assays have been suggested as important factors for disease diagnosis (Bigarre et al., ; Tamai et al., ; Williams, ). However, in the current era of molecular virology, the identification of viral infections is mainly based on examination of pathology and particle morphology, but the above‐mentioned techniques are time‐consuming and cross‐reactive and face various downstream challenges such as the lack of well‐catalogued databases for comparison, mixed nature of aquaculture environments, small number of biological samples and unknown tissue locations of infectious agents, which make the decision about diagnosis difficult.…”