Molecular detection, epidemiology, and genetic characterization of novel European field isolates of equine infectious anemia virus

Abstract

The application of molecular diagnostic techniques along with nucleotide sequence determination to permit contemporary phylogenetic analysis of European field isolates of equine infectious anemia virus (EIAV) has not been widely reported. As a result, of extensive testing instigated following the 2006 outbreak of equine infectious anemia in Italy, 24 farms with a history of exposure to this disease were included in this study. New PCR-based methods were developed, which, especially in the case of DNA preparations from peripheral blood cells, showed excellent correlation with OIE-approved agar gel immunodiffusion (AGID) tests for identifying EIAV-infected animals. In contrast, the OIE-recommended oligonucleotide primers for EIAV failed to react with any of the Italian isolates. Similar results were also obtained with samples from four Romanian farms. In addition, for the first time complete characterization of gag genes from five Italian isolates and one Romanian isolate has been achieved, along with acquisition of extensive sequence information (86% of the total gag gene) from four additional EIAV isolates (one Italian and three Romanian). Furthermore, in another 23 cases we accomplished partial characterization of gag gene sequences in the region encoding the viral matrix protein. Analysis of this information suggested that most Italian isolates were geographically restricted, somewhat reminiscent of the "clades" described for human immunodeficiency virus type 1 (HIV-1). Collectively this represents the most comprehensive genetic study of European EIAV isolates conducted to date.

FIG. 1.

Primer positions in the EIAV genome.

FIG. 2.

Phylogenetic tree demonstrating the relationships between Central European, American, and Asian EIAV strains. Posterior probabilities are indicated at each node. Topology was made with FigTree 1.2.3. The highlighted zone indicates the main Italian gag gene subtype. International sequences are as follows: NC_001450, reference genome; AF033820, Wyoming; AF016316, United Kingdom; AF327877, Liaoning; AB008197, Japan; EF418582, Canada-1; EF418585, Canada-10; and EF418581, Argentina 1. The 2006 Irish isolate of EIAV is also included (23).