Host switching of human lice to new world monkeys in South America

- Human lice are obligate permanent ecto parasites that coevolve with their host.
- Genetic studies in human lice showed a haplogroup diversity illustrated by clades A, B, C and D.
- In this study, we demonstrate that Pediculus mjobergi, a New World monkey louse was originally a human louse.
- The host switch of this louse happened thousands of years ago when the first humans reached the America.

The coevolution between a host and its obligate parasite is exemplified in the sucking lice that infest primates. In the context of close lice-host partnerships and cospeciation, Pediculus mjobergi, the louse of New World primates, has long been puzzling because its morphology resembles that of human lice. To investigate the possibility that P. mjobergi was transmitted to monkeys from the first humans who set foot on the American continent thousands of years ago, we obtained and compared P. mjobergi lice collected from howler monkeys from Argentina to human lice gathered from a remote and isolated village in Amazonia that has escaped globalization.Morphological examinations were first conducted and verified the similarity between the monkey and human lice.The molecular characterization of several nuclear and mitochondrial genetic markers in the two types of lice revealed that one of the P. mjobergi specimens had a unique haplotype that clustered with the haplotypes of Amazonian head lice that are prevalent in tropical regions in the Americas, a natural habitat of New World monkeys.Because this phylogenetic group forms a separate branch within the clade of lice from humans that were of American origin, this finding indicates that human lice have transferred to New World monkeys.