Molecular Epidemiology of EVA: 2006 Occurrence in the US

2006 was witness to perhaps the most widespread occurrence of EVA yet recorded in the USA or indeed elsewhere. Dissemination of the virus was confirmed in 10 states and outbreaks of the disease confirmed to occur a 9 to 10 month period. The World Organization for Animal Health (OlE) designated EVA reference laboratory at the Gluck Equine Research Center which was directly involved in providing diagnostic and investigational support in the course of this occurrence was in a unique position to collect and archive a large number of clinical and necropsy specimens from affected animals. Samples included fetal tissues from cases of abortions, blood leukocytes and serum from acutely infected horses, and sequential semen samples from stallions that became carriers after the outbreak. In addition, cell culture isolates of these viruses were stored at -80°C. This is a unique resource to characterize the origin and spread of the EAV in the course of this occurrence and to determine the genetic variation that occurs during the widespread dissemination of EAV and occurrence of the disease over a very extended period. In this study, we propose to investigate the genetic divergence that may take place in the virus in relation to its spatial and temporal distribution to several states in 2006 and early 2007. Specifically, we seek to establish the original source of EAV associated with the index premises in New Mexico (NM) and to identify the conserved and variable regions in the virus genome in the course of occurrence and in the semen of stallions that became persistently infected on some of the EVA-affected premises. To achieve these objectives, we will characterize the genes that encode the structural protein genes of the virus and completely sequence the genome of selected EAV isolates collected from different states over the duration of the occurrence. Sequence determination and phylogenetic analysis based on the gene that encodes the major envelope glycoprotein of EAV should enable us to identify the origin of the virus responsible for this occurrence. The complete genome sequence of key isolates from different states and of EAV recovered from sequential semen samples from carrier stallions should enable us to identify mutational hot spots in the virus genome that are subjected to change in the course of a very extended occurrence of EVA, and also provide us with a more robust comparison of genetic relationships between EAV isolates.