The oldest gammaherpesvirus lineage infects mammals and belongs to the genus Lymphocryptovirus the second-oldest lineage infects bats and belongs to the genus Rhadinovirus. Among the members of Gammaherpesvirinae, those found in bats and primates represent the oldest lineages, with the three subfamilies of the Herpesviridae arising between 180 and 220 million years ago ( 1). When long-term evolutionary trends are taken into account and when stringent analysis is used, host specificity fails to explain the host and viral evolutionary relationships, as many herpesviruses are able to infect a broad range of hosts or show evidence of having crossed species barriers in the past ( Figure 1). However, this notion is apparent only if a specific viral lineage is examined over a narrow taxonomic distribution-closely related hosts as determined by phylogeny. Like all herpesviruses, gammaherpesviruses are considered to be mainly host specific. GAMMAHERPESVIRUSES: AN ORIGIN IN CROSS-SPECIES TRANSMISSION However, it has become evident that, despite following overall coevolutionary principles, many herpesviruses may not be strictly host specific some are capable of crossing species barriers and infecting distantly related species, and some have zoonotic potential. Many herpesviruses have coevolved with their specific host species over millions of years. Advances in sequencing technology have led to the discovery of a plethora of novel herpesviruses (or their genomic sequences) over the past decade, which has helped to provide insights into the evolutionary history and host specificity of these viruses in mammals. The Herpesviridae family is further divided into three subfamilies: Alphaherpesvirinae, Betaherpesvirinae, and Gammaherpesvirinae. Herpesvirales is divided into three virus families: Alloherpesviridae, Malacoherpesviridae, and Herpesviridae. The order Herpesvirales comprises viruses with a large double-stranded DNA genome that are known to infect phyla as divergent as the Mollusca and the Chordata (fish, reptiles, amphibians, birds, and mammals). We discuss the challenges of such infections in several endangered species in the absence of efficient immunization or therapeutic options. Some infections result from herpesviruses that are endemic in the species that is primarily affected, and some result from herpesviruses that cause fatal disease after infection of non-definitive hosts. We here summarize herpesvirus infections in wild mammals that in many cases are endangered, in both natural and captive settings. Even with this general concept in mind, investigators have recognized interspecies transmission of several members of the Herpesviridae family, often with fatal outcomes in non-definitive hosts-that is, animals that have no or only a limited role in virus transmission. Species specificity is thought to result from host-virus coevolutionary processes over the long term. It is generally accepted that herpesviruses are primarily species specific, although a species can be infected by different herpesviruses. Herpesviruses are ubiquitous and can cause disease in all classes of vertebrates but also in animals of lower taxa, including molluscs.
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