An ancient American origin of hepatitis B virus

Human hepatitis B viruses (HBV) are found in human populations all around the world. They can be grouped into ten genotypes named A to J (each with their own subgenotypes).

The genotypes have a distinct geographical distribution as you can see in the map below (Source):

Hepatitis B virus global distribution of genotyhpes.

A can be found in Africa, Asia, Europe and North America. B in Eastern and Southeastern Asia. C in the same region and Central Asia. D in India and western Eurasia. E a recent apparition, found exclusively in Africa (not taken to the Americas with slave trading and probably 200 years old only - read more).

F and H are exclusive to South and Central America.

And here is the unusual thing, thse F and H genotypes are distinct from all the other ones: they branch from the phylogenetic tree as a separate and earlier branch as can be seen in the following trees from different authors:

HBV phylogenetic tree.Credits

HBV, another phylogenetic tree Note location of chimps and gorillas.Credits

HBV, a phylogenetic tree. See the branch of the woolly monkeys by the American F and H genotypes.Credits

So where did HBV originate? And here is the difficult question which cannot be answered by the usual Out of Africa theory (originated in African apes and passed on to humans there, spreading out of Africa as our ancestors migrated across the globe, reaching America last).

This time the evidence does not point towards a clear African origin. It seems that the oldest and most distant branch is rooted in America.

Margaret Littlejohn, Stephen Locarnini, and Lilly Yuen describe the five theories about HBV's origin and their shortcomings:

• New World origin (out of South America), and then reached the Old World after European discovery in 1492.
• Cospeciation: evolved in parallel in certain primate species over the past tens of millions of years.
• Coevolution as anatomically modern humans (AMH) migrated out of Africa. Caveat: "it does not fit with the close genetic relationships observed between primate and human HBV. Another inconsistency is that Native Americans predominantly have genotype F infections, whereas northeast-Asians, who are their closest relatives genetically, have genotypes B and C infections."
• Cross-species transmission, between human and nonhuman primates.
• Bat origin

The authors interestingly point out that "Given the arguments for and against each of these five theories, it is probable that HBV evolution cannot be explained by any single theory. The reality probably involves cospecies evolution within birds, rodents, and bats, followed by a series of cross-species transmission events to explain the close relationship between human and nonhuman primate HBVs observed today. Challenges for any unifying theory include the high level of genome divergence observed between HBV sequences of New World woolly monkeys and other nonhuman primates, w hich cannot be explained by the cross-species transmission theory, and also that HBV has only been detected in rodent species of the New World. If HBV coevolved with avian, rodent, and primate species, then why is it not found in all rodent and primate species? In addition, if HBV emerged out of Africa with AMH, then why are people from the New World, who are genetically most closely related to humans in the Far East, predominantly infected with HBV genotypes F and H rather than the genetically unrelated HBV genotypes B and C that are found in the Far East?"

As you can see, the American F variant and its presence in the New World woolly monkeys stand firmly against an Out of Africa origin.

Finally the paper mentions archaic hominins (Neanderthals, Denisovans and our admixing with them): "The influence of these various groups of archaic humans on the evolutionary history of HBV would be difficult to decipher. However, the possibility that human HBV may have originated, at least in part, from these archaic humans should not be discounted."

It is likely that it originated in the Americas in an Archaic (H. erectus) group and then moved into Asia and Africa (the most recent variant "E" is African after all!).

But Out of Africa is hard to beat. The author of a paper that studied HBV found in 7,000 year-old remains in Eurasia, is quoted here as follows:

"... it is still unclear how old HBV actually is. "It could be much older. It could even be coming out of Africa, which would explain why chimpanzees and gorillas fall together with the oldest HPV genomes" he adds. "That could be one explanation, but we also find it in the new world and new world monkeys and old world monkeys separated 60 million years ago, so it's very unlikely it's that old. There's lots of open question marks here."

But, he is mistaken, the gorillas and chimpanzees HBV does not align with the "oldest" groups (see second tree image further up), they lie closer to the more recent Eurasian variants..."

As usual, when an odd thing appears in the Americas which confronts the Out Of Africa theory, orthodox science finds it hard to explain them away and support the OOA theory.

Merry Christmas and Seasons Greetings to all our readers. And a Great 2019 for everyone!

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