Dados do Trabalho

Título

Genetic divergence of Necator americanus variants parallels the time scale of Homo sapiens continental migrations during the Pleistocene

Introdução

Hookworm infection persists focally in impoverished communities in developing countries. Necator americanus is the most prevalent and geographically disperse human hookworm. Sequencing of cytochrome c oxidase subunit 1 (cox1) reveals substructuring in N. americanus populations, suggesting that it could be divided into two variants, consisting of specimens from Africa and Asia.

Objetivo(s)

To assess evolutionary relationships of distinct Necator americanus lineages.

Material e Métodos

We analyzed 36 cox1 sequences from human hookworms from Piauí and Ceará states (northeastern Brazil) and 33 orthologous sequences retrieved from GenBank (465 bp). We performed Maximum-likelihood and Bayesian analysis.

Resultados e Conclusão

Two strongly-supported clades were characterized, the first corresponding to N. americanus, and the second corresponding to Necator spp. (circulating among humans and non-human primates in Africa, probably Necator gorillae). The N. americanus clade could be divided into three main clusters: the first with Brazilian and Asian sequences (China), the second with Brazilian sequences and one African sequence (Togo) and the third with only Asian sequences (China). The molecular-dating analysis suggested that the two clades dividing N. americanus and Necator sp. began to diverge during the middle Pleistocene (300,000 years ago). The time of origin of Necator sp. clade is estimated to fall approximately in the middle Pleistocene (150,000 years ago). Moreover, the most recent common ancestor among African and Asian N. americanus groups was in the late Pleistocene (approximately 60,000 years ago). Discussion/Conclusions. The "Out of Africa" theory is the dominant model of the geographic expansion of Homo sapiens and proposes a single origin of modern humans in Africa, from where they spread reaching Asia by around 65,000–50,000 years ago. The time scale parallels between N. americanus lineages genetic divergence and human continental migrations suggest the presence of hookworm infection in the populations that dispersed from Africa. N. americanus circulating in northeastern Brazil has a dual origin (African and Asian), which can be explained by the settlement and colonization of South America. During the middle Pleistocene (300,000 years ago) – and therefore before "out-of-Africa" dispersal of modern humans – a common ancestor of Necator americanus and Necator gorillae may have circulated zoonotically between humans and non-human primates.

Palavras-chave

Necator americanus; hookworms, Out-of-Africa model; evolution