Herpesvirus infections in ruminants and elephants

In the order Herpesvirales, the family Herpesviridae contains numerous viruses isolated from various ruminant species and from elephants. Viruses currently identified in ruminants belong to subfamily Alphaherpesvirinae, which includes bovine herpesvirus 1 responsible for infectious bovine rhinotracheitis, and subfamily Gammaherpesvirinae, which includes alcelaphine herpesvirus 1, causative agent of malignant catarrhal fever. Viruses isolated from elephants belong to the subfamilies Beta-and Gammaherpesvirinae. The betaherpesviruses cause a deadly hemorrhagic disease sporadically observed in elephants kept in circuses and zoos. Herpesviruses evolved over a very long time period by cospeciation with their host species. The nucleotide substitution rate is very low. However two mechanisms are important for the evolution of herpesvirus populations: viral latent persistence and a high recombination rate. There are probably many more herpesviruses infecting ruminants and elephants in the biosphere. For instance, eight herpesvirus species are currently recognised in the human species, and a similar diversity can be expected in other mammalian species. Viral discovery, based on new molecular technologies, opens new prospects, with the identification of new viral species not associated with clinical signs.