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Year 2011 - Volume 31, Number 4
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Experimental infection of calves with recombinants of bovine herpesvirus 5 defective in glycoprotein E (gE), thymidine kinase (TK) and both, gE/TK, 31(4):319-325
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ABSTRACT.- Santos C.M.B., Anziliero D., Bauermann F.V., Brum M.C.S., Weiblen R. & Flores E.F. 2011. Experimental infection of calves with recombinants of bovine herpesvirus 5 defective in glycoprotein E (gE), thymidine kinase (TK) and both, gE/TK. Pesquisa Veterinária Brasileira 31(4):319-325. Departamento de Medicina Veterinária Preventiva, Universidade Federal de Santa Maria, Camobi, Santa Maria, RS 97105-900, Brazil. E-mail: eduardofurtadoflores@gmail.com
This article describes an investigation on the virulence/attenuation of bovine herpesvirus type 5 (BoHV-5) recombinants deleted in the genes encoding glycoprotein E (BoHV-5gED), thymidine kinase (BoHV-5TKD), and both gE and TK (BoHV-5gEDTKD). Seronegative calves (80 to 90 days-old) inoculated with the parental strain (SV-507/99, n=5) shed virus in nasal secretions for up to 15 days (average 10.8 days). Duration of virus shedding was 11 days for BoHV-5gD, 9.6 days for BoHV-5TKD and 6.2 days for BoHV-5gEDTKD groups. The highest titers were observed between days 1 and 6 post-infection (pi) for SV-507/99 (106.8TCID50/mL), 105.1TCID50/mL (BoHV-5gED), 105.9TCID50/mL (BoHV-5TKD) and 104.7TCID50/mL (BoHV-5gEDTKD). Calves inoculated with the parental virus presented anorexia, profound apathy and loss of body condition. Two calves were euthanized in extremis on days 10 and 11 pi; infectious virus was recovered from several areas of the brain. In contrast, calves inoculated with the recombinants remained healthy and a few presented a mild and transient nasal secretion. Dexamethasone (Dx) administration at day 42 pi resulted in virus shedding by all controls calves (mean duration 3.7 days), by 2/5 of BoHV-5TKD calves (two days) and 2/5 of BoHV-5gED (one day). No virus shedding was detected in BoHV-5gEDTKD calves upon Dx treatment. PCR examination of brain sections of calves euthanized at day 30 post Dx treatment revealed the presence of latent viral DNA widely distributed in the brain of SV-507/99 calves. Latent viral DNA was detected in a few sections (3/30) of the brains of BoHV-5gED calves and was not detected in the brains of calves inoculated with BoHV-5TKD and BoHV-5gEDTKD. These results show that the single BoHV-5 mutants (gE and tk-deleted) are attenuated for calves and establish and/or reactivate latent infection inefficiently. The double mutant BoHV-5gEDTKD is fully attenuated and appears not to establish or not reactivate efficiently from latent infection. Thus, these recombinants, especially the double mutant BoHV-5gEDTKD, display an adequate phenotype for use in modified-live vaccine formulations. |
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