الفهرس 
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Abstract
Equine herpes virus is one of the most important pathogen infecting equine all over the world. It caused highly devastating effect, resulting in outcomes other than respiratory disease such as abortion, neonatal death or neurological disease. characterization of the orf 68 (Us2) is one of the goals of this study. Partial Us2 GST recombinant protein had been produced and purified to be used in Guinea pig immunize for producing polyclonal Ab. To investigate the role and significance of ORF68 in Ab4p infection, different mutant viruses based on Ab4p BAC. system had been reconstituted. Multi-step growth experiments were conducted to evaluate the growth properties of the mutant viruses. Viruses behavior and growth were nearly the same at the different cell types but the viruses grew more efficiently on FHK cells, Ab4p∆ORF68 grew 1log less than the parent one, while the Ab4p∆ORF68R none sense growth was similar or slight decreased than the parent one. To assess a possible contribution of Us2 to the cell-to-cell spread of EHV-1, plaque size measurement revealed that Us2 play important role in virus transmission from cell to another. Subcellular localization of the cloned GFP orf 68 gene product showed late expression with intranuclear localization while using IFAT it was mainly at nuclear membrane. ELISA technique had been used to investigate the prevalence of EHV antibody in El Menoufia governerorate, the highest prevalence rate was in Alshohadaa and Tala, while the lowest rate was recorded in Berket Elsabee and Shebin Elkom. Finally we can conclude that Us2 is not an essential gene but its product is essential for virus penetration and spreading from cells to another one, EHV infections are widespread among horses in El Menoufia governerorate, and thus, constitute a health risk for other animals in the region.