Molecular identification of iridoviruses infecting various sturgeon species in Europe.

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.

First detection of Cyprinid Herpesvirus 2 (CyHV-2) in goldfish (Carassius auratus) in France.

Massive mortalities of Carassius auratus (L.) occurred in a farm in France during summer 2014. Fish presented anorexia, loss of scales and large amounts of mucus on the gills. Necrosis of the distal tip of the filament and the lamellae, combined with fusion of the lamellae, was observed, as well as necrosis in the hematopoietic organs and in the digestive tract. The histological examination led to hypothesize the implication of a virus in the mortality. The presence of cyprinid herpesvirus 2 (CyHV-2) in dead fish was demonstrated by amplification and sequencing of portions of the DNA polymerase and helicase genes, both sequences exhibiting 100% identity with CyHV-2 from Japan. In an attempt to find genetic markers of variation, two regions containing tandem repeats in the Japanese genome were amplified from a virus-positive sample from the present outbreak. A first region (mB) was fully identical to the Japanese isolate. However, the second region (mA) exhibited a range of deletions and substitutions compared to CyHV-2 from Japan. This is the first report of CyHV-2 in France in association with mortality of goldfish and the first identification of a molecular marker for its tracing.