Equine arteritis virus (EAV) infection occurs throughout much of the world. Serologic surveys of horse populations indicate that exposure is common but clinical signs are uncommon so many infections are subclinical or inapparent. However the virus can cause acute "flu'-like" illness in horses including swelling of the legs. Most importantly EVA can induce abortion in mares after the 3rd month of pregnancy, death in foals, and persistentle infect the reproductive tract of stallions. The recent surge of shipped semen has many wondering if we are on the verge of a remarkable outbreak of abortion storms. Theories have been developed and tested as to why this disease happens episodically. This article discusses these issues, clinical signs, treatment and prognosis of this disease.

Most infections occur from contact with aerosolized respiratory secretions. But in the past few years it has been confirmed that venereal transmission from carrier stallions is the most important route of infection as it introduces the virus into populations of pregnant mares. There the newly infected mares spread the disease through respiratory secretions. Note Well : both natural service and artificial insemination can result in infection in susceptible mare populations.

The infection rate may range as high as 50% in some stallion populations and may persist for years in a stallion. It should be noted that the carrier state has never been detected in a stallion vaccinated with the MLV vaccine ARVAC by Fort Dodge Animal Health, Ft Dodge, Iowa, USA. However, these vaccinates may, upon exposure to the virus, have the virus reproduce and cause temporary shedding for a period. We recommend vaccination of active stallions.

More Information University of California has recently done some major research into EVA. This work has been funded by the Grayson-Jockey Club Research Foundation Development of improved vaccines and serologic (blood) tests for the control of equine arteritis virus infection of horses N. James MacLachlan et al Researchers used four structural proteins of EAV expressed in insect cells (recombinant proteins) to immunize laboratory animals and horses. The researchers then determined if inoculated animals produced antibodies to these proteins and, if so, whether antibodies to specific proteins could provide protective immunity to a subsequent challenge with EAV and thus function as a subunit vaccine. These four recombinant proteins were also used to create an ELISA based assay to develop an improved serologic al test for the diagnosis of EAV infection. The assay was validated using a large panel of sera from horses that were vaccinated with the MLV vaccine, naturally and experimentally infected with EAV, and including sera from persistently infected stallions. Results Interpretation: This research characterized the horse's humoral immune response (antibody) to EAV, and therefore, is critical for the development of improved tests and vaccines to diagnose and prevent EAV infection. This study clearly identified the M protein of EAV as the most immunogenic viral protein. Interestingly, persistently infected (carrier) stallions more consistently recognized the N protein then did non-carrier stallions. The researchers also established that, although the GL protein expresses the neutralization determinants of EAV, GL protein alone did not confer a protective antibody response in laboratory animals. Therefore, alternative strategies must be developed in any efficacious subunit vaccine. This study provides information that is necessary to develop appropriate policies and regulations pertaining to EAV infection of the horse. Neutralization determinants of equine arteritis virus N. James MacLachlan Equine arteritis virus (EAV) is distributed throughout the world and causes periodic outbreaks of equine viral arteritis (EVA). Although there is only one serotype of EAV, preliminary studies with virus strains from around the world indicated that there is considerable difference between them. The effect of this genetic variation on the virus' behavior is unknown. This researches aim was to define and explore the EAV genome and the neutralization determinants of EAV using antibodies, EMVs, and a large panel of EAV field strains that were isolated in Europe and North America over the last 40 years. Results and Interpretation: Developed a new serological (blood) test to detect previous exposure of horses to EAV. This research identified the neutralization determinants of EAV which is prerequisite to the development of improved vaccines to prevent EAV infection of the horse. The researchers also defined the horse's immune response to EAV and developed reagents th at potentially can be used in improved diagnostic tests to detect previous EAV infection of horses as well as in vaccines to prevent such infection. Genetic diversity of equine arteritis virus during persistent infection of stallions N. James MacLachlan Experients were designed to determine the genetic variation of EAV in the semen of persistently infected stallions. Results and Interpretation: These studies clearly demonstrated that the genetic variation of EAV that occurs during persistent infection of stallions leads to the periodic emergence of strains that are capable of initiating outbreaks of EVA. The genetic variability that occurs during persistent infection of the stallion, contrasts markedly with the relative genetic stability of viruses that circulated during outbreaks of EVA. This study has better defined the molecular epidemiology of EAV infection, and will contribute to efforts to develop better guidelines for movement and trade of stallions and their semen. Ultimately, this study should also lead to the development of improved procedures to diagnose and prevent EAV infection of horses.