Ruminant alphaherpesviruses related to bovine herpesvirus 1 (BoHV-1) are a cluster of viruses antigenically and genetically closely related. The prototype of this cluster, BoHV-1, is a major pathogen of cattle associated with various clinical manifestations including infectious bovine rhinotracheitis (IBR) and infectious pustular vulvovaginitis (IPV). IBR is a disease of major economic concern in many parts of the world and especially in Europe, both in countries where this infection has been eradicated and in those where the control of IBR is currently or will be undertaken. The massive use of vaccination allowed a significant reduction of the number of IBR clinical cases. However, the existence of closely related viruses to BoHV-1 is a threat for IBR eradication programmes. Consequently, the main objective of the present work is dedicated to afford a better knowledge of the interaction between alphaherpesviruses and their ruminant hosts in order to contribute to improve the control of IBR.
To meet the objective, two approaches have been developed: the study of the viral diversity aiming to extend both epidemiological and virological data about ruminant alphaherpesviruses related to BoHV-1 and the study of the heterologous protection aiming to protect minor ruminant species by the concept of the “cascade” vaccination.
Illustrating the problematic of the cluster of ruminant alphaherpesviruses related to BoHV-1, an original situation has been described recently in Belgium. During 2001 and 2002 hunting seasons, 28.9% of red deer were detected seropositive to BoHV-1. Due to an apparent lack of contact between cattle and red deer, it was suggested that a BoHV-1 related virus was spreading in the Belgian red deer population. Thus, the first isolation of cervid herpesvirus 1 (CvHV-1) in wild fauna is reported, which brings the opportunity to deeper analyse the antigenic, genomic and genetic relationship between BoHV-1 and its related ruminant alphaherpesviruses.
This isolation demonstrates that a ruminant can be strongly identified as BoHV-1 positive while in actual fact it is infected with a related but distinct alphaherpesvirus and this ruminant will be declared as false positive. The problem is even greater when these viruses become latent allowing their possible reactivation and persistence for a very long time in their ecological niches. It is necessary to have tests which can differentiate related alphaherpesviruses that infect different ruminant species. The control of IBR relies on the use of BoHV-1 gB and gE blocking enzyme linked immunosorbent assays (ELISA) in order to differentiate infected and gE-negative vaccinated animals. Knowing that CpHV-1 is the most distant virus from BoHV-1, it can be hypothesised that a BoHV-1 gB blocking ELISA detects CpHV-1 but that CpHV-1 infection could be discriminated by a BoHV-1 gE blocking ELISA. CpHV-1 being mainly distributed in the Mediterranean part of Europe as Greece, Spain and Italy, the analysis was performed with field serums collected in France with the aim to update the epidemiological situation of the infection in Europe.
Besides BoHV-1, CpHV-1 is the most relevant infection in Europe but is sadly neglected. The first reason is that economic losses are restricted to a herd level in contrast with IBR that brings an economical impact at a country level. The second reason is that goat is considered as a minor species. In this context, the problem is still not big enough for commercial interest towards vaccine development. The European Union has recently pointed out the problem of minor uses and minor species and allowed off label use of veterinary medicinal products or the use of a product licensed for a major species when an authorised veterinary medicinal product is not available (“cascade” principle). Goat being a minor species and CpHV-1 sharing close antigenic and genetic properties with BoHV-1, a live attenuated gE-negative BoHV-1 vaccine has been assessed in goats to protect against either a nasal or a genital CpHV-1 infection.