Mitochondrial DNA reveals species composition and phylogenetic relationships of hookworms in northeastern Brazil.

ABSTRACT

Hookworm infection persists focally in rural communities in Brazil. In this study, we analyze the mitochondrial nucleotide sequences obtained from hookworms infecting humans in order to characterize species composition and assess their genetic diversity and phylogenetic relationships. Field expeditions and cross-sectional surveys were carried out in three Brazilian municipalities from 2013 to 2017 Nossa Senhora de Nazaré (n = 605) and Teresina (n = 297), in the state of Piauí, and Russas (n = 213) in the State of Ceará. Parasitological methods were used to evaluate fecal samples. Hookworm-positive samples had a partial mtDNA cox1 amplified and sequenced. Maximum-likelihood and Bayesian analysis demonstrated two strongly-supported clades, including Group A, corresponding to Necator americanus, and Groups B and C, corresponding to Necator sp. Group A was divided into three main clusters A1 grouped with Asian sequences, A2 grouped with African sequences, and A3 had only Asian sequences. Group B was closely related to Necator sp., showing a sequence similarity of 98%-99% with African samples circulating zoonotically among humans and non-human primates. Twenty three N. americanus haplotypes were identified. N. americanus Median-Joining network revealed three distinct groups, designated again as A1, A2, and A3. Group A1 presented a star-like shape, with one dominant haplotype. The molecular dating suggested that the two clades dividing N. americanus and Necator sp. began to diverge during the middle Pleistocene. The most recent common ancestor among N. americanus groups was dated to the late Pleistocene. Hookworms circulating in the studied communities are structured in well-defined subpopulations presenting both Asian and African genetic backgrounds. This reveals a double origin for hookworms in northeastern Brazil and opens up new possibilities in phylogeographic, evolutionary, and molecular epidemiological studies in regions where hookworms persists focally, despite control efforts. The presence of potentially zoonotic species and the specific identification of Necator sp. should be further investigated.