Date Published: April 30, 2019
Publisher: Public Library of Science
Author(s): Victor Hugo Borba, José Roberto Machado-Silva, Matthieu Le Bailly, Alena Mayo Iñiguez, Ben J Mans.
Paleoparasitology, the study of parasites in the past, brings the knowledge of where and when they occurred in preterit populations. Some groups of parasites, as capillariids, have a complex and controversial systematic, hindering the paleoparasitological diagnosis. In this article, we synthesized the occurrence of capillariids in both the New and the Old World in ancient times, and discussed the difficulty of the diagnosis of species and the strategies for identification. The present review also shows the current status of the phylogeny in capillariids and indicates the necessity to try new approaches for a better understanding of capillariid paleodistribution.
For the systematic review, a predefined guideline defined by PRISMA was used. The articles collected were identified, screened, and included in the review following criteria for eligibility. The current status of the phylogeny of capillariids was accessed using MUSCLE, Bioedit v.7.0.5 and MEGA v. 7.0.21 programs.
The review discussed 38 articles that presented information about capillariids in past populations. Most of capillariid eggs found in the New and Old World were not identified. However, Calodium hepaticum eggs were the most identified, as some from Eucoleus genus. It was observed that sites from the New World had a better chance for capillariid egg identification, due to previous knowledge of its host, when compared to the Old World. In the 18S rDNA phylogenetic analyses, two datasets were constructed, one including sequences from 7 Moravec’s genera, where 3 genus-specific clusters, with high bootstrap values, could be observed for Capillaria (ML = 99%, NJ = 96%), Eucoleus (ML / NJ = 100%) and Paratrichosoma (ML / NJ = 100%). A fourth cluster of 18S rDNA dataset I revealed lack of definition of Pearsonema and Aonchotheca genera. The 18S rDNA dataset II comprised 8 Moravec’s genera and defined 3 clusters, 2 genus-specific for Eucoleus (ML = 99%, NJ = 100%) and Capillaria (ML / NJ = 98%). The third 18S rDNA dataset II cluster included 6 genera and exhibited, once again, Pearsonema and Aonchotheca poor discrimination. The cox1 gene data consist of 4 Moravec’s genera, and in spite of grouping some species-specific clusters, did not show genera-specific definition.
Despite the numerous archaeological findings, both in the New and the Old Worlds, the identification of capillariid species based on the morphology and morphometry of eggs remains imprecise, often resulting in a generic diagnosis of a group or morphotype of capillariid. Capillariid is one of the most diverse group of helminths recovered in archaeological sites. The phylogenetic trees produced in this study showed limited genetic information available, unresolved genera and incongruence with the classical taxonomy. The elucidation of the paleodistribution of capillariids can give insights of the ancient host-parasite associations but also in modern sceneries.
Over 300 species of capillariids have been described throughout the world in different vertebrate hosts, as fishes, amphibians, reptiles, birds or mammals . The difficulty of identification, due to the small size of the specimens and the few morphological structures that are characteristics for species identification, make their systematic and taxonomy one of the most complex among the phylum Nematoda. Another factor that hinders their classification is the phenotypic plasticity caused by different hosts, infection sites and locations . In 1982, Moravec changed the classification of the group when proposed 16 genus of capillariids . After that, a number of new genera, synonyms and reclassifications have been proposed.
In this systematic review we followed a guideline defined by PRISMA . This process generated a PRISMA flow chart illustrated in Fig 1. Basically, the literature was identified as possible articles, then screened and accesses for eligibility and included in the review.
Despite the numerous archaeological findings, both in the New and the Old Worlds, the identification of capillariid species based on the morphology and morphometry of eggs remains imprecise, often resulting in a generic diagnosis of a group of capillariid. The challenge in working with the characterization of egg morphology and morphometry is clearly due to the diversity of species and the similarity of eggs from different species. A coupled of statistic treatment have showed interesting results in the identification of taxon. However, this approach is limited by the poor knowledge on the egg morphology, mainly considering animal capillariids. Paleogenetic studies have been shown as promissory approach for identifying a variety of parasitic species in archeological materials [48–51]. Molecular techniques have not been employed in ancient capillariids and require an important development in the genetic characterization of the capillariid group.