Molecular characterization of equine infectious anaemia virus from a major outbreak in southeastern France.

This study discusses a significant outbreak of equine infectious anemia (EIA) in France in 2009. It details the molecular characterization of the virus that caused the infection in 16 horses across three related premises and analyzes it in comparison with European strands.

Beginning of the Outbreak

• The research focuses on an EIA outbreak that was reported in 2009 in southeastern France, more precisely in the Var region. This disease appeared first in a 10-year-old mare from a riding school, which showed clinical signs typical of EIA.
• During this outbreak, over 250 horses were tested for EIAV antibodies using the agar gel immunodiffusion test. Out of these, 16 horses from three different holdings were found to be positive.

Epidemiological Findings

• An epidemiological survey revealed that the three sites where infected horses were found had a connection. The link was established through the purchase and sale of horses and the use of shared or adjacent pastures.
• Despite the distances between some premises being up to 50 kilometers, the epidemiological data suggested a common origin of the virus due to shared trade and communal pasture usage.

Molecular Characterization of the Virus

• The viral molecular characterization was done by sequencing the full 1,400 base pairs of the gag gene found in the proviral DNAs extracted from the spleens of infected horses collected post-mortem.
• The phylogenetic analysis confirmed the epidemiological data as it demonstrated that the viruses isolated from the three different holdings were clustering together. This further corroborated the finding that they all had a common origin.

Comparison with European Strains

• The research found that the strains of the virus found during this outbreak differed significantly from the European strands described so far, which emphasizes the high genetic diversity of EIAV in Europe. This could imply that different mechanisms of transmission, evolving immunity, or other ecological elements may influence the viral strains present within different geographical regions.