Molecular Identification of Bovine Alpha Herpesvirus Subtype 1.1 in Field Isolates in Egypt by Phylogenetic Analysis of Glycoprotein B Gene

Bovine alphaherpesvirus 1 (BoHV-1) is an enveloped double-stranded DNA virus of Herpesviridae family.Closely related alpha herpesviruses; BoHV-1 and Bovine herpes virus-5 (BoHV-5) have the same antigenic and genetic relatedness.BoHV-1 is one of the viruses that incriminated in respiratory disease; affects the genital tract and causes significant economic losses to domestic cattle in Egypt.Although BoHV-5 mainly causes encephalitis in calves, the virus is excreted in nasal discharge under stress factors, so herpesvirus latency reactivation cycle is the hallmark of the disease.In the present study, molecular screening of 60 nasal swabs, collected from clinically suspected animals, was established by polymerase chain reaction (PCR) targeting glycoprotein B (gB) gene.Six PCR positive samples were isolated on chorioallantoic membranes (CAMs) of 11 days old Embryonated Chicken Eggs (ECEs) for three blind passages.The CAMs showed thickening and congestion at 1 st passage and typical pock lesions appeared at 3 rd passage.Indirect immunofluorescent technique (IFT) was used for confirmation of BoHV-1 presence in CAM; the CAM with clear pock lesions showed yellowish-green fluorescence under the fluorescent microscope.The phylogenetic tree constructed from partial sequencing of gB of our isolate was divided into two clades; clade 1 BoHV-1 (BoHV-1.1 and BoHV-1.2) clade 2 (BoHV-5).Our isolate showed 100% homology to BoHV-1.1 reference strains away from BoHV-5 reference strains that were clustered in the other clade.BoHV-5 reference strains were different from our isolate by 25 nucleotide substitutions, which led to five amino acid substitutions ( E316D, A378T, S410G, I425T, E429G).