Persistent infection of the genital tract and excretion of the vaccine strain after live virus immunization with bovine herpesvirus 1 (IBR/IPV virus)

Reintroduction of bovine herpes virus type 1 into Danish cattle herds during the period 1991-1995: a review of the investigations in the infected herds

In Denmark a programme for the systematic eradication of bovine herpes virus 1 (BHV-1) was completed during the years 1984 to 1991, but outbreaks due to new introductions of BHV-1 were seen. Between January 1991 and May 1994, 22 herds became infected with BHV-1, all located closely to the German border. In 1995, 61 herds were detected BHV-1 antibody positive, but they were situated in many different parts of Denmark. In order to find the source of infection owners of infected herds were interviewed, and restriction fragment pattern analysis (RFP-analysis) was performed on virus isolates from the herds with clinical outbreaks. Isolates from clinical outbreaks up to 1995 were identified as a Cooper-like strain, while 2 of those in 1995 had characteristics of a "new" strain, which had never before been identified in Denmark or elsewhere in Europe. In the described situation different transmission routes for virus seemed possible. One being a sporadic introduction of virus due to accidental contact with infected cattle near the German border or maybe due to an airborne transmission of virus over longer distance. The other, presumably a result of import of an infected animal despite the national regulations. The latter, due to an extensive trade pattern, resulted in the introduction of infected cattle into 51 BHV-1 seronegative cattle herds.

Advances in the development and evaluation of bovine herpesvirus 1 vaccines

This review deals with conventional and modern bovine herpesvirus 1 (BHV1) vaccines. Conventional vaccines are widely used to prevent clinical signs of infectious bovine rhinotracheitis. The use of conventional vaccines, however, does not appear to have resulted in reduction of the prevalence of infection. Novel BHV1 marker vaccines comprise either mutants with a deletion in one of the non-essential genes, or subunit vaccines that contain one or more glycoproteins. These marker vaccines can be used in conjunction with companion diagnostic tests to differentiate between infected and vaccinated cattle. Their efficacy has been evaluated in vaccination-challenge experiments, transmission experiments and in field trials. The results demonstrate that the marker vaccines can contribute to the eventual eradication of BHV1. However, there remains room for improvement of BHV1 marker vaccines.

Bovine herpesvirus 1 in semen of bulls and the risk of transmission: a brief review

Outbreaks of bovine herpesvirus 1 (BHV1) infections in artificial insemination centres can run a clinical or subclinical course. Clinical signs vary from mild to severe balanoposthitis and may be associated with a decrease in semen quality. After intranasal as well as intrapreputial infection, BHV1 can replicate in the preputial and penile mucosae, although the pattern of virus shedding in semen differs considerably per individual bull. Beyond the primary phase of a genital infection, BHV1 remains latent in sacral ganglia, and consequently a protracted course of intermittent virus excretion may follow. The seminal plasma rather than the sperm cells contains the BHV1. Diluting the semen before inoculating cell cultures appears to be the best method to neutralize its toxic activity and to achieve optimal virus isolation results. Detection of BHV1 in semen by polymerase chain reaction seems to be more sensitive than virus isolation. Not each extended semen straw contains virus when the virus titre in the ejaculate is low. The minimal dose to infect a cow by artificial insemination may be more than 32 infectious virus particles. Such an infection may lead to fertility disturbances, mainly endometritis. The risk of transmitting BHV1 to inseminated cows by using BHV1-seropositive bulls for artificial insemination is substantially reduced if two straws per semen batch are assayed for virus and if each positive batch is destroyed.

Changes in the bovine herpesvirus 1 genome during acute infection, after reactivation from latency, and after superinfection in the host animal

Three subtypes, as defined by HindIII restriction endonuclease (RE) analysis patterns, of bovine herpesvirus 1 (BHV 1) were used to inoculate seronegative, BHV 1-free cattle. These included: infectious bovine rhinotracheitis virus (IBRV), subtype 1.1; infectious pustular vulvovaginitis virus (IPPV) isolate K22, subtype 1.2b; and IPVV isolate FI, subtype 1.2a. Nasal, vaginal, and buffy coat samples were taken for virus isolation from each animal. RE analysis was done on virus isolates collected during acute infection, after reactivation from latency, and after reactivation followed by superinfection with a subtype of BHV 1 that differed from the primary inoculation virus. Changes occurred in the BHV 1 genome after only 1 passage in the host animal, and varied from tissue to tissue within the same animal. Viruses reactivated from latency also displayed genome variability. Only animals that received IPVV as the primary inoculation virus were successfully superinfected. After superinfection, cattle shed both superinfecting and reactivated viruses, and genome variability was observed. These data suggest that the application of RE analysis in diagnostic and epidemiologic studies of BHV 1 is limited to analysis between types and subtypes, and is not applicable for the examination of isolates from within a BHV 1 subtype.