Comparative Genome Analysis of Four Elephant Endotheliotropic Herpesviruses EEHV3, EEHV4, EEHV5 and EEHV6 from Cases of Hemorrhagic Disease or Viremia

Abstract

Summary: The genomes of three types of novel endotheliotropic herpesviruses (EEHV1A, EEHV1B and EEHV2) associated with lethal hemorrhagic disease in Asian elephants have been previously well characterized and assigned to a new Proboscivirus genus. Here we have generated 112-kb of DNA sequence data from segments of four more types of EEHV by direct targeted PCR from blood or necropsy tissue of six viremic elephants. Comparative phylogenetic analysis of nearly 30 protein-encoding genes of EEHV5 and EEHV6 show that they diverge uniformly by nearly 20% from their closest relatives, EEHV2 and EEHV1A respectively, and are likely to have similar overall gene content and genome organization. In contrast, seven EEHV3 and EEHV4 genes analysed differ from those of all other EEHVs by 37% and have a (G-plus-C)-content of 63% compared to just 42% for the others. Three strains of EEHV5 analyzed clustered into two partially chimeric subgroups EEHV5A and EEHV5B that diverge by 19% within three small non-contiguous segments totalling 6.2-kb. We conclude that all six EEHV types should be designated as independent species within a proposed new fourth Deltaherpesvirinae subfamily of mammalian herpesviruses. These likely initially diverged close to 100 million years ago when the ancestors of modern elephants split from all other placental mammals, then evolved into two major branches with high or low (G-plus-C)-content about 35 million years ago. Later additional branching events subsequently generated three paired sister taxon lineages of which EEHV1 plus EEHV6, EEHV5 plus EEHV2 and EEHV4 plus EEHV3 may represent Asian and African elephant versions, respectively. Importance: One of the factors threatening the long-term survival of endangered Asian elephants in both wild range countries and in captive breeding populations in zoos is a highly lethal hemorrhagic herpesvirus disease that has killed at least 70 young Asian elephants worldwide. The genomes of the first three types of EEHVs (or Probosciviruses) identified have been partially characterized in the preceding paper. Here we have used PCR DNA sequence analysis from multiple segments of DNA amplified directly from blood or necropsy tissue of six more selected cases of hemorrhagic disease to partially characterize four other types of EEHVs from either Asian or African elephants. We propose that all six types and two chimeric subtypes of EEHV belong to multiple lineages of both AT-rich and GC-rich branches within a new subfamily to be named the Deltaherpesvirinae, which evolved separately from all other mammalian herpesviruses about100 million years ago.