Partial genetic characterisation of a novel alloherpesvirus detected by PCR in a farmed wels catfish (Silurus glanis).

By a broad-range PCR, we detected a novel herpesvirus (HV) in the specimen of a wels catfish (Silurus glanis) presenting disseminated, carp pox-like dermal lesions all over its body. The sequence analysis of the 463-bp PCR product from the viral DNA polymerase gene indicated the presence of a hitherto unknown virus, a putative member of the family Alloherpesviridae in the sample. Another PCR, targeting the terminase gene of fish HVs, provided an additional genomic fragment of over 1,000 bp. Surprisingly, the sequence of a co-amplified, off-target PCR product revealed its origin from a putative gene homologous to ORF87 and ORF45 of cyprinid HVs and anguillid herpesvirus 1 (AngHV-1), respectively. With specific primers, designed according to the genomic maps of the cyprinid and anguillid HVs, a genomic fragment of 15 kb was also amplified and sequenced by primer walking. In phylogeny inferences, based on several genes, the putative wels catfish HV clustered closest to various cyprinid HVs or to AngHV-1. The novel virus, named as silurid herpesvirus 2, represents a distinct species in the genus Cyprinivirus. However, its association with the skin disease remains unclear.