Bovine herpesvirus-1: evaluation of genetic diversity of subtypes derived from field strains of varied clinical syndromes and their relationship to vaccine strains.

Bovine herpesvirus-1 (BoHV-1) causes significant disease in cattle. Control programs in North America incorporate vaccination with modified live viral (MLV) or killed (KV) vaccine. BoHV-1 strains are isolated from diseased animals or fetuses after vaccination. There are markers for differentiating MLV from field strains using whole-genome sequencing and analysis identifying single nucleotide polymorphisms (SNPs). Using multiple primer sets and sequencing of products permits association of BoHV-1 isolates with vaccines. To determine association between vaccine virus and strains isolated from clinical cases following vaccination, we analyzed 12 BoHV-1 isolates from animals with various clinical syndromes; 9 corresponded to BoHV-1.1 respiratory group. The remaining three corresponded to BoHV-1.2b, typically found in genital tracts of cattle. Four BoHV-1 isolates were identical to a vaccine strain; three were from post-vaccination abortion episodes with typical herpetic lesions whose dams had received MLV vaccine during pregnancy, and one from a heifer given a related MLV vaccine; Sequences of two respiratory isolates perfectly matched mutations characterizing RLB106 strain, a temperature sensitive mutant used in intranasal and parenteral vaccines. The last three respiratory strains clearly appeared related to a group of MLV vaccines. Previously the MLV vaccines were grouped into four groups based on SNPs patterns. In contrast with above-mentioned isolates that closely matched SNP patterns of their respective MLV vaccine virus, these 3 strains both lacked some and possessed a number of additional mutations compared to a group of MLV vaccine viral genome. Finding BoHV-1.2b in respiratory cases indicates focus should be given BoHV-1.2b as an emerging virus or a virus not recognized nor fully characterized in BRD.

Kennedy, the early sixties, and visitation by the angel of death.

The inaugural issue of Pathologia Veterinaria in 1964 contained the first detailed account of lesions in aborted fetuses following natural, experimental, and postvaccinal infection with bovine herpesvirus 1 (BoHV-1). The article, written by pathologists Kennedy and Richards, described diagnostic gross and histologic features in 13 bovine fetuses. The authors provided clinical and epidemiologic features of 1 postvaccination outbreak, including the absence of clinical signs in infected dams and the propensity for abortions to occur after 6 months' gestation. Subsequent field and experimental studies corroborated and expanded these observations. As a result of this and later reports, veterinarians became alert to the association between infectious bovine rhinotracheitis and abortion, including the risks of exposing pregnant cattle to live vaccinal BoHV-1. Methods were developed to corroborate a morphologic diagnosis of herpetic abortion in cattle, including immunofluorescence, immunohistochemistry, and polymerase chain reaction methods. Outbreaks of postvaccinal BoHV-1 abortion in the United States began to be reported with apparently increased frequency in the early 2000s. This coincided with licensure in 2003 of modified live BoHV-1 vaccines intended for use in pregnant cattle, which are now sold by 3 manufacturers. Ten recent herd episodes of postvaccinal BoHV-1 abortion are reported. All 10 BoHV-1 isolates had single-nucleotide polymorphism (SNPs) profiles previously identified in a group of BoHV-1 isolates that contains vaccine strains, based on a BoHV-1 SNP classification system. They lacked SNP features typical of those in characterized field-type strains of BoHV-1.