Molecular epidemiological investigation of Ascaris genotypes in China based on single‐strand conformation polymorphism analysis of ribosomal DNA

Abstract

Using a single-strand conformation polymorphism-based approach, we investigated nucleotide variation in part of the first internal transcribed spacer (pITS-1) of nuclear ribosomal DNA within and among a large number of Ascaris individuals from humans and pigs from six endemic regions in China, and examined the frequency of the different genotypes of Ascaris in relation to host species and geographical origin. Five different SSCP genotypes (G1-G5) were recorded for human Ascaris (n = 486), of which three (genotypes G1-G3) were detected for pig Ascaris (n = 329). Of the five Ascaris genotypes detected, genotype G1 predominantly infected humans (approximately 63-74%) whereas genotype G3 infected mainly pigs (approximately 79-86%), indicating that each of these genotypes has a particular host affiliation. In contrast, the frequencies of the other three genotypes was substantially lower for each of the two host species. The findings also suggested that the rate of cross infection of Ascaris between humans and pigs is relatively low and that gene flow between the predominant genotypes is limited, consistent with previous proposals for endemic regions in other countries. While the nature and extent of nucleotide variation in the pITS-1 (and the proposal of host affiliated Ascaris populations) may relate to "introgression" or "lineage sorting and retention of ancentral polymorphism", other explanations are possible. Evidence of multiple pITS-1 sequence types in some Ascaris individuals representing particular genotypes (e.g., G2 and G5) may suggest hybridization between human- and pig-affiliated Ascaris. This aspect and the species status of Ascaris (from each host species) warrant future experimental testing, employing the pig/Ascaris model and the present electrophoretic approach.*

Genetic heterogeneity and phylogeny of Trichuris spp. from captive non-human primates based on ribosomal DNA sequence data

“…in ascaridoid nematodes (Abollo et al, 2003;Peng et al, 2003;Cavallero et al, 2014). Cross-infection and hybridization between human and porcine species have been reported also in Trichuris spp.…”

A parasitological paradox: Why is ascarid infection so rare in the prehistoric Americas?

“…It is essential to specify whether A. lumbricoides eggs are fertilized or unfertilized (Figure 3). Unfertilized eggs signify precarious conditions for transmission and patent infection, or even cross infection between human and pig species (Peng et al, 2003) However, T. trichiura eggs were observed in greater numbers even in environments where high temperatures did not prevail in the past. Therefore, unless A. lumbricoides decomposed10 times more than T. trichiura (considering the recorded egg production for these species), a change in egg production over time cannot be discarded.…”

Assessing the zoonotic potential ofAscaris suumandTrichuris suis: looking to the future from an analysis of the past

“…Application of a similar molecular approach to 115 sympatric worms obtained from humans and pigs in China (Peng et al, 1998) led to an analogous conclusion. This was later confirmed by the use of singlestrand conformation polymorphism (SSCP) to detect nucleotide variation in the internal transcribed spacer (ITS) region and mitochondrial cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes of 486 and 329 worms from humans and pigs, respectively, collected from six provinces in China (Peng et al, 2003(Peng et al, , 2005. Even though no fixed genetic differences were identified (i.e.…”