The nematode parasite
Ascaris lumbricoides
infects the digestive tracts of over 1.4 billion people
worldwide, and its sister species,
Ascaris suum
, has infected
a countless number of domesticated and feral pigs. It is generally thought that
the putative ancestor to these worms infected either humans or pigs, but with
the advent of domestication, they had ample opportunity to jump to a new host
and subsequently specialize and evolve into a new species. While nuclear DNA markers
decisively separate the two populations, mitochondrial sequences reveal that three
major haplotypes are found in
A. suum and in
A. lumbricoides, indicating
either occasional hybridization, causing introgression of gene trees, or retention
of polymorphism dating back to the original ancestral species. This article provides
an illustration of the combined contribution of parasitology, archaeoparasitology,
genetics and paleogenetics to the history of ascariasis. We specifically investigate
the molecular history of ascariasis in humans by sequencing DNA from the eggs
of Ascaris found among ancient archeological remains. The findings of this paleogenetic
survey will explain whether the three mitochondrial haplotypes result from recent
hybridization and introgression, due to intensive human-pig interaction, or whether
their co-occurrence predates pig husbandry, perhaps dating back to the common
ancestor. We hope to show how human-pig interaction has shaped the recent evolutionary
history of this disease, perhaps revealing the identity of the ancestral host.
