Abstract
Since the original description and naming of Ascaris lumbricoides from humans by Linnaeus in 1758 and later of Ascaris suum from pigs by Goeze 1782, these species have been considered to be valid. Four hypotheses relative to the conspecificity or lack thereof (and thus origin of these species) are possible: 1) Ascaris lumbricoides (usually infecting humans) and Ascaris suum (recorded mostly from pigs) are both valid species, with the two species originating via a speciation event from a common ancestor sometime before the domestication of pigs by humans, or 2) Ascaris lumbricoides in humans is derived directly from the species A. suum found in pigs with A. suum then existing as a persistent ancestor after formation of A. lumbricoides, or 3) Ascaris suum is derived directly from A. lumbricoides with the persistent ancestor being A. lumbricoides and A. suum being the newly derived species, and finally, 4) Ascaris lumbricoides and A. suum are the same species, this hypothesis being supported by studies showing both low morphological and low genetic divergence at several genes. We present and discuss paleoparasitological and genetic evidence that complement new data to evaluate the origin and evolution of Ascaris spp. in humans and pigs, and the uniqueness of the species in both hosts. Finally, we conclude that Ascaris lumbricoides and A. suum are a single species and that the name A. lumbricoides Linnaeus 1758 has taxonomic priority; therefore A. suum Goeze 1782 should be considered a synonym of A. lumbricoides.
Highlights
Since the original description and naming of Ascaris lumbricoides from humans by Linnaeus in 1758 and later of Ascaris suum from pigs by Goeze 1782, these species have been considered to be valid
Ascaris lumbricoides Linnaeus 1758 is a parasite of Homo sapiens, and Ascaris suum Goeze 1782 occurs in pigs (Sus scrofa Linnaeus 1758)
2) Ascaris lumbricoides in humans is derived directly from the species A. suum found in pigs with A. suum existing as a persistent ancestor
Summary
The origin of Ascaris spp. is still not well understood. Results obtained from experimental infections and molecular methods have been inconclusive, and before this time, none of the published studies answered the question of whether A. lumbricoides and A. suum are truly distinct species. All samples were collected from people in close contact with pigs and data showed common haplotypes in Ascaris sp. Taking into account the history of close contact of humans and wild pigs, estimated at about 10,000 years before present, the verified nematode crossinfections between humans and pigs, and the documented hybridization that occurred between A. lumbricoides and A. suum, together with the recent insights about high levels of genetic similarity between the complete mtDNA genomes of A. lumbricoides and A. suum [6,9,10,11,18,40,42,59] we conclude that only a single interbreeding population of Ascaris exists, and the genotypic and phenotypic differences are only manifested at the population level. We recommend synonymizing these two species, with the name Ascaris lumbricoides Linnaeus 1758 taking priority over Ascaris suum Goeze 1782
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