The present invention relates to an in vivo equine disease model for equine herpesvirus-1 neurological disease comprising a horse having a low pre-exposure level of herpesvirus-specific CTL precursors and/or is approximately 20 years of age or older wherein the horse is experimentally infected with a neuropathogenic strain of equine herpesvirus or a mutant thereof. The invention includes a method of preparing an in vivo equine disease model for equine herpesvirus-1 neurological disease comprising obtaining a horse that possesses low pre-infection levels of EHV-1 specific CTL precursors and/or is approximately 20 years of age or older and inoculating the horse intranasally with an effective infecting amount of a neuropathogenic strain of EHV-1. A particularly preferred method involves the advanced neurological disease stage when the experimental horse presents clinical signs of myeloencephalopathy. Additionally, the invention concerns a method of quantifying the risk factors and predicting the development of clinical neurologic signs of equine herpesvirus-1 neurological disease in a horse comprising the steps of (a) determining the pre-infection CTLp frequency to be less than approximately 40 EHV-1 specific CTLp per 106 PBMC and (b) determining the post-infection viremic load following exposure to EHV-1 to be approximately 10-fold or more over the viremic load present in horses following exposure to a non-neuropathogenic strain of EHV-1. Also described in the invention is the determination of the risk of developing the clinical neurologic signs by use of an equation y=a+bx wherein y is the peak viremic load, a=2.97, b=−0.027 and the variable x is the pre-infection CTLp frequency. Lastly, the invention deals with a new live, attenuated vaccine formulation that is effective against neurologic disease due to equine herpesvirus-1.
