Antigenic variation among isolates of infectious salmon anaemia virus correlates with genetic variation of the viral haemagglutinin gene

Abstract

Infectious salmon anaemia virus (ISAV), an orthomyxovirus-like virus, is an important fish pathogen in marine aquaculture. Virus neutralization of 24 ISAV isolates in the TO cell line using rabbit antisera to the whole virus and comparative sequence analysis of their haemagglutinin (HA) genes have allowed elaboration on the variation of ISAV isolates. The 24 viruses were neutralized to varying degrees, revealing two major antigenic groups, one American and one European. Sequence analysis of the HA gene also revealed two groups of viruses (genotypes) that correlated with the antigenic groupings. The two HA subtypes had nucleotide sequence identity of only 79n4 % and amino acid sequence identity of 84n5 % whereas, within each subtype, the sequence identities were 90n7 % or higher. This grouping was also evident upon phylogenetic analysis, which revealed two distinct phylogenetic families. Between the two groups, the amino acid sequence was most variable in the C-terminal region and included deletions of 4-16 amino acids in all isolates relative to ISAV isolate RPC/NB-980 280-2. In order to view the relationships among these sequences and the HA sequences of the established orthomyxoviruses, a second phylogenetic tree was constructed which showed the ISAV sequences to be more closely related to sequences from Influenzavirus A and Influenzavirus B than to sequences from Influenzavirus C and Thogotovirus. The extensive deletions in the gene of European ISAV isolates lead us to speculate that the archetypal ISAV was probably of Canadian origin.

Bioinformatic Analysis of the Genome of Infectious Salmon Anemia Virus Associated with Outbreaks with High Mortality in Chile

“…With the appearance of more isolates, it was established that strains from Norway, Scotland, the Faroe Islands, and Nova Scotia belong to the European genotype. On the other hand, Canadian and North American isolates are considered North American genotypes (13,36,63). Based on the similarity to segments 2 and 8 of Canadian virus isolates in 2001, Chilean ISAV isolated from infected Coho salmon was initially classified as the North American genotype (34,56).…”

“…It has been suggested that the diversity of HPR sequences provides antigenic variability (56). HPR was proposed as a virulence marker, with the most virulent strains containing HPR4 (36,37,50,51), but some authors do not agree with that conclusion (65). Although every HPR in Chile has been identified, the most abundant is the genotype 7b, which originates from Norway (35).…”

Correlation of Virus Replication in Tissues with Histologic Lesions in Atlantic Salmon Experimentally Infected with Infectious Salmon Anemia Virus

“…Viruses U5575-1 and RPC-01-0593-1 were originally isolated from disease outbreaks in Nova Scotia and New Brunswick, Canada, respectively, whereas Norway 810/9/99 was from Norway. 26 The viruses were grown in TO cell line as described previously. 26 In brief, the cells were grown at room temperature (22Њ C) in Eagle's minimum essential medium (BioWhittaker Inc., Walkersville, MD, USA) containing Hanks' salt and sodium bicarbonate (2.2 g/liter), supplemented with 292 mM L-glutamine (Sigma-Aldrich, Mississauga, ON, Canada), 1% nonessential amino acids (SigmaAldrich), 100 g ml Ϫ1 gentamicin (Sigma-Aldrich), and 10% fetal bovine serum (FBS).…”

Comparative aspects of infectious salmon anemia virus, an orthomyxovirus of fish, to influenza viruses

“…The evolutionary distance to infl uenza viruses of birds and mammals is vast, as can be displayed by phylogenic relationships based upon nucleotide or amino acid sequences [4]. The amino acid identity between the ISAV proteins and those of other orthomyxoviruses is as low as 13-25% [15,16,[19][20][21][22].…”