title: Bovine herpesvirus 1 modified live virus vaccines for cattle reproduction: Balancing protection with undesired effects.
abstract: Bovine herpesvirus 1 (BoHV-1) has long been associated with reproductive failure in cattle following infection of the ovary and/or fetus. Vaccination prior to breeding has been an effective approach to lessen the impact of BoHV-1 on reproduction. Prior studies in the 1980s and 1990s established the susceptibility of the ovary and particularly the corpus luteum (CL) to BoHV-1 infection. A series of studies at breeding time established that: (1) in naïve animals, the CL was the major target of BoHV-1 pathology; (2) CL lesions occurred within 4-9 days after estrus; (3) similar lesions was seen with BoHV-1 MLV vaccines; (4) ovarian lesions varied by the vaccine strain used; (5) progesterone decreased with or without CL lesions; and (6) following reactivation of BoHV-1 latent infection, ovaries could become reinfected in the face of BoHV-1 immunity. Large scale field studies demonstrated that conception was highest in animals previously vaccinated and boostered with inactivated vaccine compared to animals revaccinated with MLV. In the early 2000s, to get a label claim to vaccinate calves nursing pregnant cows, safety study outlines were approved by USDA-APHIS CVB. These studies were designed to determine the effect of revaccination with MLV during pregnancy on previously vaccinated cows and were not rigorous enough to confirm complete fetal safety. As designed these studies showed no difference in reproductive loss between the previously vaccinated animals and the animals revaccinated ∼4, 7 and 9 months later, leading to the label approval for MLV vaccination in pregnant cows. Subsequent investigations by diagnostic laboratories found an increase in BoHV-1 reproductive loss after the approval for use in pregnant animals. A method was developed to differentiate IBR vaccine strains from field strains. Analysis of viruses from 31 cases from 2009-2016 indicated that all 31 isolates matched with vaccine strains. Going forward, it will be necessary to develop vaccine approaches that use non-abortifacient, nonlatent BoHV-1 vaccines that develop lifelong immunity, protecting the animal while doing no harm to the fetus.
authors.affiliation: Department of Veterinary and Biomedical Sciences, South Dakota State University, Brookings, SD 57007, United States. Electronic address: Christopher.Chase@sdstate.edu.
authors.forename: Christopher C L
authors.initials: CCL
authors.lastname: Chase
authors.affiliation: Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, OK 74078, United States.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Fulton
authors.affiliation: Department of Veterinary Science, University of Wyoming, Laramie, WY 82070, United States.
authors.forename: Donal
authors.initials: D
authors.lastname: O'Toole
authors.affiliation: Department of Veterinary and Biomedical Sciences, South Dakota State University, Brookings, SD 57007, United States.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Gillette
authors.affiliation: Department of Veterinary and Biomedical Sciences, South Dakota State University, Brookings, SD 57007, United States.
authors.forename: Russell F
authors.initials: RF
authors.lastname: Daly
authors.affiliation: Department of Animal Science, South Dakota State University, Brookings, SD 57007, United States.
authors.forename: George
authors.initials: G
authors.lastname: Perry
authors.affiliation: Department of Veterinary and Biomedical Sciences, South Dakota State University, Brookings, SD 57007, United States.
authors.forename: Travis
authors.initials: T
authors.lastname: Clement
mesh_terms: D000818:Animals; D002417:Cattle; D005260:Female; D005306:Fertilization; D006566:Herpesviridae Infections / Q000517:prevention & control / Q000662:veterinary* / Q000821:virology; D007242:Herpesvirus 1, Bovine / Q000276:immunology*; D007117:Immunization, Secondary / Q000662:veterinary; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000517:prevention & control / Q000662:veterinary* / Q000821:virology; D012098:Reproduction; D014611:Vaccination / Q000662:veterinary*; D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated; D014765:Viral Vaccines / Q000276:immunology*
chemical_list: D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated; D014765:Viral Vaccines
keywords: Bovine; Conception; Herpesvirus; Reproduction