In vitro-generated interspecific recombinants between bovine herpesviruses 1 and 5 show attenuated replication characteristics and establish latency in the natural host

Four groups of four 3-month-old calves of both genders were intranasally inoculated with either the recombinant or parental viruses. A control group of two animals was also included. Viral excretion and clinical signs were monitored after infection. Histopathological examination of the central nervous system (CNS) was performed and the establishment of latency in trigeminal ganglia was analyzed by PCR. The humoral response was also evaluated using ELISA tests.Three out of four animals from the BoHV-5 infected group excreted virus for 4-10 days. Two calves shed R1ΔgC virus for one day. In R2ΔgI and BoHV-1.2ΔgCΔgI groups, infectious virus was isolated only after two or three blind passages. None of the infected animals developed neurological signs, although those infected with BoHV-5 showed histopathological evidence of viral infection. Latent viral DNA was detected in at least one calf from each infected group. Serum and/or mucosal antibodies were detected in all groups.Both BoHV-1/-5 recombinants and the BoHV-1 parental strain are attenuated in calves, although they are able to replicate in animals at low rates and to establish latent infections.Bovine herpesviruses 1 (BoHV-1) and 5 (BoHV-5) are two closely related alphaherpesviruses infecting cattle. BoHV-1 respiratory infection is usually associated with infectious bovine rhinotracheitis, abortion, and systemic infection in neonates [1]. BoHV-5 infection induces respiratory and nervous diseases, i.e. meningoencephalitis [2]. Both viruses are neurotropic and establish a life-long latent infection in neurons of sensory ganglia [2,3].BoHV-1 infection is present in all continents, although there are differences in prevalence and incidence [4]. In the USA, Canada, Australia and New Zealand the seroprevalence of BoHV-1 infection is variable but may be very high. BoHV-1 is also present in European countries, where a variety of control programs are carried out. Concerning South American countries, BoHV-1 infection is ende