Whipworms in humans and pigs: origins and demography.

Mohamed B F Hawash,Azmi Al-Jubury,Arve Leewillingham,Mads F Bertelsen,Philip J Cooper,Peter Nejsum,D Tim J Littlewood,Martha Betson,Jennifer Ketzis,Xing-Quan Zhu

doi:10.1186/s13071-016-1325-8

Abstract

BackgroundTrichuris suis and T. trichiura are two different whipworm species that infect pigs and humans, respectively. T. suis is found in pigs worldwide while T. trichiura is responsible for nearly 460 million infections in people, mainly in areas of poor sanitation in tropical and subtropical areas. The evolutionary relationship and the historical factors responsible for this worldwide distribution are poorly understood. In this study, we aimed to reconstruct the demographic history of Trichuris in humans and pigs, the evolutionary origin of Trichuris in these hosts and factors responsible for parasite dispersal globally.MethodsParts of the mitochondrial nad1 and rrnL genes were sequenced followed by population genetic and phylogenetic analyses. Populations of Trichuris examined were recovered from humans (n = 31), pigs (n = 58) and non-human primates (n = 49) in different countries on different continents, namely Denmark, USA, Uganda, Ecuador, China and St. Kitts (Caribbean). Additional sequences available from GenBank were incorporated into the analyses.ResultsWe found no differentiation between human-derived Trichuris in Uganda and the majority of the Trichuris samples from non-human primates suggesting a common African origin of the parasite, which then was transmitted to Asia and further to South America. On the other hand, there was no differentiation between pig-derived Trichuris from Europe and the New World suggesting dispersal relates to human activities by transporting pigs and their parasites through colonisation and trade. Evidence for recent pig transport from China to Ecuador and from Europe to Uganda was also observed from their parasites. In contrast, there was high genetic differentiation between the pig Trichuris in Denmark and China in concordance with the host genetics.ConclusionsWe found evidence for an African origin of T. trichiura which were then transmitted with human ancestors to Asia and further to South America. A host shift to pigs may have occurred in Asia from where T. suis seems to have been transmitted globally by a combination of natural host dispersal and anthropogenic factors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1325-8) contains supplementary material, which is available to authorized users.

Highlights

Trichuris suis and T. trichiura are two different whipworm species that infect pigs and humans, respectively
Phylogenetic analyses We used two mitochondrial markers to infer the genetic relationships and the evolutionary history between different Trichuris populations obtained from humans, non-human primates and pigs from various geographical regions (Table 1)
It is noteworthy that two samples showed double peaks in the chromatogram of the nad1 gene and gave conflicting signals for the rrnL gene

Summary

Introduction

Trichuris suis and T. trichiura are two different whipworm species that infect pigs and humans, respectively. T. suis is found in pigs worldwide while T. trichiura is responsible for nearly 460 million infections in people, mainly in areas of poor sanitation in tropical and subtropical areas. We aimed to reconstruct the demographic history of Trichuris in humans and pigs, the evolutionary origin of Trichuris in these hosts and factors responsible for parasite dispersal globally. The prevalence of whipworms in non-human primates is generally high and despite the fact that the taxonomic status is Population genetic tools provide a valuable opportunity to investigate the epidemiological history and transmission of parasites and have been adopted to study. Reconstruction of the epidemiological and demographic history gives us a window into the past to see which factors facilitated spread or the introduction of the parasites to new regions [5]. The introduction of W. bancrofti to Papua New Guinea cannot be explained by ancient human migration but must have been introduced through more recent human migration [8]

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