Durer's rhinocerosA while ago I talked about evolution of the herpesviruses, and I said:

We know of 200-odd herpesviruses so far, and more are being identified practically daily. It’s likely that virtually every animal species has its own set of unique herpesviruses. This is probably because herpesviruses are very host-restricted (rarely infecting more than a single species) and set up latent, life-long infection. When an animal population speciates, its complement of herpesviruses speciates along with it.

Word of my blog post spread like wildfire (as is inevitable for a blog that is read by upward of five people, including my mother) and Duncan McGeoch hastened to correct me with a fascinating paper now in pre-print form at the Journal of Virology:
Ehlers, B., Dural, G., Yasmum, N., Lembo, T., de Thoisy, B., Ryser-Degiorgis, M., Ulrich, R.G., McGeoch, D.J. (2008). Novel mammalian herpesviruses and lineages within the Gammaherpesvirinae: Cospeciation and interspecies transfer. Journal of Virology DOI: 10.1128/JVI.02646-07

Host species Virus name
Gorilla GgorRHV-1
Squirrel monkey SsciGHV-2
Asian elephant EmaxGHV-1
Spotted hyena CcroGHV-1
Lion PleoGHV-1
Pygmy hippopotamus HlibGHV-1
Chamois SbarRHV-1
Bearded pig RrupGHV-1
Babirusa BbabRHV-1
Mountain zebra EzebGHV-1
Black rhinoceros DbicGHV-1
Tapir TterGHV-1
Tree shrew TbelGHV-1
Common shrew SaraGHV-1

McGeoch’s group went herpesvirus hunting (“Be vewwy, vewwy quiet!”) and — supporting at least the first part of my quote here — found no less than 14 brand-new gammaherpesviruses. (They would have found 16 new viruses, but their elephant gammaherpesvirus was described earlier this year when Wellehan et al earlier this year found 6 new gammaherpesviruses of elephants, rock hyraxes, and manatees,1 and their gorilla virus was described a few years ago by Gessain’s group2 )

The new gammaherpesviruses come from shrews, tapirs, rhinocerous, zebras, babirussas, pygmy hippos, and so forth (see the table to the right, and see the paper itself for accession numbers, I’m not going to copy them all down). They used a fiddly, if not conceptually difficult, technique to get a reasonable sequence length (3.4 kb) for phylogenetic analysis, rather than the couple hundred base pairs that this sort of virus fishing expedition usually yields, and then lined up the newly expanded complement of gammaherpesviruses, which now includes no less than 45 viruses.

Babirusa skullI won’t reproduce their phylogenetic tree here (the actual figure from the preprint has the “ACCEPTED” watermark stamped all over it, and I don’t have time to get 45 virus sequences and re-build the alignment according to their description). The interesting thing about this tree is that it tells a somewhat different story than an earlier and more limited analysis.

In earlier analyses of Herpesviridae phylogeny, it was possible to discern within each of the subfamilies a substantial degree of congruence in tree branching pattern with the corresponding pattern for lineages of the mammalian hosts, and this was taken as indicating extensive cospeciation of herpesviruses and hosts.

Even in these previous analyses, the gammaherpesviruses were the worst match for the co-speciation hypothesis — that is, closely-related gammaherpesviruses were found in mammalian hosts that were not very closely related, suggesting that the viruses’ ancestors might have jumped hosts at some point. That observation was even more true in this larger set, especially in the more ancient divisions:

… applicability of cospeciational interpretation declines further with the extensive detail now available for the GHV tree. … the deeper branching details of the tree prove rather unproductive for constructing any unified coevolutionary correspondence across host lineages. In particular, the two deepest distinct lineages, i.e. LCV and EmaxGHV-1, are not simultaneously compatible with a single cospeciational scheme, and in the MF2 clade the unresolved nodes for major lineages do not enable any compelling interpretation. On the other hand, clear dispersed examples of cospeciation can be seen in the terminal branchings within major lineages. … In summary, there are substantial indications in the GHV tree of evolution both by cospeciation with host lineages and by transfer between widely distinct hosts.

(My emphasis.)

There are at least two really interesting implications from this work. First, McGeoch’s group supports the previously-proposed notion that there may be more human herpesviruses yet to be found, because there are major divisions of the gammaherpesvirus families that don’t yet have human representatives. Second, although I’m not aware of any instances of non-human herpesviruses successfully3 infecting humans, this work suggests that at least in the past, and therefore likely today, gammaherpesviruses could make interspecies leaps.

Just something else to watch for.

  1. Wellehan JFX, Johnson AJ, Childress AL, Harr KE, Isaza R (August 19, 2007) Six novel gammaherpesviruses of Afrotheria provide insight into the early divergence of the Gammaherpesvirinae. Vet Microbiol. doi:10.1016/j.vetmic.2007.08.024 []
  2. Either Lacoste V, Mauclre P, Dubreuil G, Lewis J, Georges-Courbot M, et al. (2000) Virology: KSHV-like herpesviruses in chimps and gorillas . Nature 407.:151-152
    Lacoste V, Mauclère P, Dubreuil G, Lewis J, Georges-Courbot MC, et al. (September 2001) A novel gamma 2-herpesvirus of the Rhadinovirus 2 lineage in chimpanzees. Genome Res 11.:1511-9.
    I didn’t check the sequences to see which reference is McGeoch’s gorilla virus.[]
  3. Where “successfully” means not merely infecting and killing occasional individuals, but actually spreading from person to person — I know about herpesvirus B and so on[]