Infectious bovine rhinotracheitis/infectious pustular vulvovaginitis and infectious pustular balanoposthitis

Infectious bovine rhinotracheitis/infectious pustular vulvovaginitis and infectious pustular balanoposthitis

L A BABIUK, S VAN DRUNEN LITTEL-VAN DEN HURK AND S K TIKOO
Infectious bovine rhinotracheitis/infectious pustular vulvovaginitis and infectious pustular balanoposthitis

Introduction

In 1913 a vulvovaginitis of cattle called Bläschenausschlag was first described in Europe.129 It was subsequently shown to be caused by a virus that was isolated from the genital tract of an affected cow.52, 123 In parallel, an acute contagious febrile infection of cattle characterized by an intense inflammatory reaction of the upper respiratory tract, which was accompanied by dyspnoea, nasal discharge and depression, was reported and called infectious bovine rhinotracheitis (IBR) to describe its infectious nature and hallmark which is rhinotracheitis.67 Although these two distinct syndromes have been referred to in the past as ‘red nose’, ‘dust pneumonia’, infectious necrotic rhinotracheitis, coital exanthema, vesicular venereal disease, or infectious pustular vulvovaginitis (IPV), it has been accepted that they all refer to infection with either bovine herpesvirus 1 (BHV-1) subtype 1 or 2.32, 48, 49, 72, 106

Although rhinotracheitis, pustular vulvovaginitis and pustular balanoposthitis are the most common manifestations of disease caused by BHV-1, the sites of infection of the virus are not strictly restricted to the respiratory or genital tracts; other syndromes caused by it include those associated with conjunctivitis, abortion or meningoencephalitis.32 It must, however, be borne in mind that bovine herpesvirus 5 is more frequently associated with fatal meningoencephalitis in cattle than BHV-1.

Aetiology

Bovine herpesvirus 1 is a member of the family Herpeviridae, subfamily Alphaherpesvirinae, genus Varicellavirus. 94 Isolation and characterization of the infectious agent have clearly demonstrated that BHV-1 can cause the clinical syn dromes mentioned above. Although it is common that an animal suffers simultaneously from more than one syndrome, particularly respiratory disease and conjunctivitis, it is rare for an animal to suffer concurrently from both respiratory and genital infections.

The BHV-1 virion contains a double-stranded DNA genome of 135 to 140 kbp.74, 125 As do other members of the alphaherpesviruses, BHV-1 codes for approximately 70 proteins. Most of the transcripts have now been identified and with the recent completion of the sequencing of the entire BHV-1 genome, all the potential open reading frames have been identified.101 Most of the genes identified in BHV-1 have, with a few exceptions, a similar counterpart in other alphaherpesviruses, such as herpes simplex virus.122

The genomic arrangement of BHV-1 is typical of group D herpesviruses in that the genome is divided into a unique long (UL) segment of approximately 102 to 104 kbp and a unique short (US) segment of approximately 10,5 to 11 kbp flanked by inverted repeat regions of approximately 24 kbp.74, 101, 125 The genomic organization into UL and US segments allows the US sequence to invert relative to the UL sequence, giving rise to the two isomeric forms of the genome.74 In parallel with the sequencing of the genome, a detailed analysis of the transcripts encoded for by the genome using Northern blotting has led to the identification of the majority of transcripts produced during BHV-1 infection.101, 122 Similar to other alphaherpesviruses, the genome is transcribed in three different stages, viz. immediate early (α), early (β), and late (γ) genes.95 The late gene transcripts occur at the time of viral DNA synthesis.

Based on genomic analysis and viral peptide patterns, BHV-1 strains have been classified into subtypes:106 infectious bovine rhinotracheitis strains comprise subtype 1, whereas IPV/IPB strains fall into subtype 2. Although all the neurological strains were initially also grouped with BHV-1, the one most frequently associated with fatal meningoencephalitis in cattle has been reclassified as bovine herpesvirus 5 based on its unique genomic characteristics.96, 106 All isolates of BHV-1 appear to be antigenically related and even after extensive in vitro or in vivo passage, the isolates retain their antigenicity.33 Studies have clearly indicated the genetic stability of the virus which has significant implications for vaccine development and diagnosis. However, there is some variation in restriction endonuclease DNA fragment patterns that may be useful for epidemiological studies in some situations.29, 77

Although the virus is an enveloped virus, thereby being susceptible to disinfectants which destroy the lipid envelope, it is generally accepted that it is relatively stable in the environment. Thus, it may be between animals by nasal secretions or saliva in feed bunks. In vitro, virus can remain viable for a number of days at room temperature in cell culture media.

The virus is extremely easy to culture in any primary or established bovine cell cultures. Since many bovine cell lines are persistently infected with bovine viral diarrhoea virus, care must be exercised in interpreting results of virus isolation. Although BHV-1 can infect cell lines of other animal species, the replication is either abortive or only occurs to a low level.

Epidemiology

Bovine herpesvirus 1 infections occur worldwide. Although cattle are the principal host of BHV-1, other ruminants such as goats, several members of the deer family, water buffalo (Bubalus bubalis)...

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