Heirloom parasites and souvenirs
Some parasites that infest humans are uniquely ours: they only infect humans and have done so for hundreds of thousands of years. Though we may not like to think about it, these parasites are only here because their ancestors have inhabited an unbroken line of human bodies for countless generations – all the way back beyond our distant ancestors who walked out of Africa. Surely no other species on Earth can claim such a close association with people – not even our long-domesticated crops and animals. They are our “heirloom parasites” – some call them “old friends” – and they can tell us a lot about our past.
Other parasites are generalists: they infect humans regularly but they can also infect other animals and do so whenever the opportunity presents itself. Some of these may be heirloom parasites that spread from humans. Others likely infected other species first and crossed to humans later. These last, along with parasites that only infect humans rarely and by accident, are our “souvenirs.”
Both of these things are intriguing when you think about it: that over the course of , perhaps millions of years, we never failed to – unintentionally – give our heirloom parasites what they needed to survive; and that we are still picking up new souvenirs today, in numerous unplanned, unobserved, unexpected ways. It says a lot about the devilishly unbreakable life cycles of parasites.
Araújo, Adauto, Luiz F. Ferreira, Karl J. Reinhard et al. 2008 “Parasites as Probes for Prehistoric Human Migrations?” (galley proofs) Natural Resources, School of Papers in Natural Resources, University of Nebraska – Lincoln.
Araújo, Adauto and Luiz Fernando Ferreira. 2000 “Paleoparasitology and the Antiquity of Human Host-parasite Relationships.” Memórias do Instituto Oswaldo Cruz On-line. Suppl. 1 Nov.