Ascariasis in China

Human-type and pig-type Ascaris hybrids found in pigs

The discovery of hybrids between Ascaris lumbricoides and Ascaris suum has complicated our understanding of the relationship between the two species. We examined the same Ascaris specimens (48 from humans and 48 from pigs) using two methods: microsatellite markers combined with Bayesian clustering and PCR-RFLP of the nuclear internal transcribed spacer region. The results obtained by the two methods were inconsistent but showed that hybrid Ascaris identified through both approaches could infect pigs. The results of this study suggest that PCR-RFLP of ITS alone is not suitable for molecular identification of human-type and pig-type Ascaris hybrids. Use of multiple SSR markers combined with Bayesian analysis was the most reliable method in our study. Our results indicate that, in addition to host-specific Ascaris types, there may be some that do not show host specificity. Our results show for the first time that hybrid individuals can infect pigs as well as humans. This study has important theoretical and practical implications, including suggesting the need to re-evaluate long-term ascariasis control strategies.

Phylogeography of Ascaris lumbricoides and A. suum from China

In order to obtain further understanding of genetic structure and evolutionary relationship of Ascaris from humans and pigs, phylogeography study on 12 populations from six endemic regions in China was conducted using mitochondrial DNA markers (cytochrome c oxidase subunit 1 (COX1) and NAD1) and the software programs of DnaSP 5.0, Arlequin 3.0, MEGA 4.0, and NETWORK 4.5.1.6. Results showed that (a) genetic diversity of Ascaris varied with hosts and locations, but no distinct geographical distribution pattern was found, (b) a higher level of genetic diversity and differentiation was found in pig-derived populations in contrast to human-derived ones, and in populations of human-derived Ascaris from the southern regions in comparison to that from the middle and northern locations, but similar geographical difference was not observed within pig-derived populations, (c) historical population expanding was detected from a large part of human-derived Ascaris populations but not in pig-derived Ascaris, (d) a high level of gene flow was detected between human- and pig-derived Ascaris and also among human-derived populations, and (e) network analysis from haplotype of COX1 indicated an ancestral haplotype from human-derived Ascaris. In conclusion, the present study revealed new information on Ascaris on the aspects of genetic diversity, population differentiation and historical demographic patterns, gene flow, phylogenesis reconstruction, and haplotype network, discussed the results with historical demographic migration of humans and domestication of wild boar in China, and raised a different assumption about the evolutionary relationship of the two roundworms. This study should have certain enlightenment for the epidemiology and the evolutionary and taxonomy relationship of Ascaris from humans and pigs.

Recent insights into the epidemiology and genetics of Ascaris in China using molecular tools

Ascaris is a large parasitic roundworm (nematode) of the small intestine of humans and pigs, which causes the socio-economically important disease, ascariasis. To better understand the relationship of Ascaris between the 2 host species, recent studies in China have focused on investigating the genetics and epidemiology of Ascaris from humans and pigs using a mutation scanning-based approach. Findings provided support for a low level of gene flow between the human and porcine Ascaris populations. Extending the studies of genotypic variability within Ascaris from humans and pigs, experimental infections of mice and pigs with selected genotypes of Ascaris were carried out. Initial results indicate that there is a significant difference in the ability of Ascaris eggs of genotype G1 (derived from human) and G3 (derived from pig) to infect and establish as adults in pigs, supporting the difference in the frequencies of these genotypes in natural Ascaris populations between pigs and humans in China. Taken together, current information supports that there is limited cross-infection of Ascaris between humans and pigs in endemic regions and that pigs are not a significant reservoir of human infection with the adult nematode in such areas.

Experimental infections of pigs and mice with selected genotypes of Ascaris

Extending a previous investigation of the genotypic variability within Ascaris from humans and pigs, experimental infections of mice and pigs with selected genotypes of Ascaris were performed in the present study to explore possible host affiliation. Initial findings indicate that there is a significant difference in the ability of Ascaris eggs of genotype G1 (derived from human) and G3 (derived from pig) to infect and establish as larvae in mice and as adults in pigs, supporting the difference in the frequencies of the genotypes reported previously in natural Ascaris populations in pigs and humans in areas in China endemic for ascariasis.

Mutation scanning-coupled analysis of haplotypic variability in mitochondrial DNA regions reveals low gene flow between human and porcineAscaris in endemic regions of China

Haplotypic variation within and among the Ascaris populations representing six provinces in China was investigated. Mitochondrial DNA regions in the cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes were amplified by PCR from total genomic DNA samples (n > 720) from Ascaris individuals from humans and pigs, and subjected to mutation scanning and subsequent selective sequencing. For the cox1, ten different electrophoretic profiles were recorded for human Ascaris, and the same number for pig Ascaris, one of them being common to both host species. For the nad1, 11 different profiles were detected for human Ascaris, and 15 for pig Ascaris. Having defined all haplotypes (20 for pcox1 and 26 for pnad1) by sequencing, their frequencies were estimated in each of the two host species and each of the six provinces. For each mitochondrial region, the frequency of the different haplotypes varied considerably, depending on host species and geographical origin. Analysis of the sequence data (representing all haplotypes for each mitochondrial locus) by F-statistics indicated restricted gene flow between human Ascaris and pig Ascaris, and supported the conclusions from previous molecular epidemiological investigations that pigs are not a significant source of Ascaris infection in humans in endemic regions.

Ascaris egg profiles in human faeces: biological and epidemiological implications

Since 2 morphological forms (fertilized and unfertilized) of egg can be produced by Ascaris, infected humans can release in their faeces fertilized eggs only (FEO), unfertilized eggs only (UEO) or both fertilized and unfertilized eggs (FUE) (designated herein as the 3 different egg profiles). Epidemiologically, fertilized eggs are of significance as they enable effective transmission of the parasite. This study, for the first time, characterizes the Ascaris egg profiles in human faeces in an endemic region of China, explores possible host- and parasite-factors related to these profiles, and discusses the biological and epidemiological implications of the findings. The 3 egg profiles were recorded throughout the study period of 2 years, and the overall percentages of people with FEO, FUE and UEO profiles were approximately 41-47%, 32-42% and 17-21%, respectively. The overall number of unfertilized eggs for the entire population accounted for approximately 6-9% of all eggs excreted. The different Ascaris egg profiles showed no correlation to host gender, but they did relate to age and worm burden of the host and to the sex ratio and developmental status of the parasite. While an annual universal anthelmintic treatment resulted in some fluctuation in the values of individual egg profiles, the general features of these profiles remained similar throughout the study period. The findings of this study should have significant implications for understanding transmission patterns of Ascaris and for the implementation of control measures against ascariasis in endemic regions.

Cellular responses and cytokine profiles in Ascaris lumbricoides and Trichuris trichiura infected patients

The impact of intestinal helminth infection, i.e. Ascaris lumbricoides and Trichuris trichiura, on cellular responsiveness and cytokine production was investigated in young adults. Ascaris-specific cellular responsiveness was higher in parasite-free endemic controls than in patients infected with T. trichiura, or A. lumbricoides, or patients co-infected with both parasites. Also, mitogen-induced tumour necrosis factor (TNF)-alpha, interleukin (IL)-12 and interferon (IFN)-gamma secretion by peripheral blood mononuclear cells (PBMC) was higher in negative endemic controls than in infected individuals. Ascaris antigen-specific production of TNF-alpha, IL-12 and IFN-gamma was low in singly Ascaris as well as in co-infected patients, whereas secretion of IL-10 and IL-13 was elevated and similarly high in all patient groups. The detection of Trichuris-specific and Ascaris-specific IgG4 revealed significantly higher serum antibody levels in Trichuris or Ascaris patients when compared to endemic controls (P < 0.05), whereas parasite-specific IgE antibody levels were similarly high in infected individuals and in endemic controls. In summary, chronically infected Ascaris and Trichuris patients with a high parasite load presented reduced cellular reactivity and lower type 1 TNF-alpha, IFN-gamma and IL-12 responses when compared with endemic controls, whereas type 2 IL-10 and IL-13 productions were similar in all groups from the endemic area. The former may support parasite persistence, whereas substantial type 2 cytokine release may promote protective immunity, suggesting an adaptation of the host to control the parasite burden while minimizing immune-mediated host self-damage.

Gastrointestinal nematodes, nutrition and immunity: breaking the negative spiral

Nutritionists have long understood that intestinal nematode parasites have deleterious effects on host nutritional status, but only recently has the importance of malnutrition as a predisposing factor to intestinal nematodes been recognized. Here we review experimental and field studies on the effects of protein, energy, zinc, vitamin A, and iron deficiencies on gastrointestinal (GI) nematodes of humans, livestock, and laboratory rodents, and draw certain conclusions about the state of our current understanding. In general, malnutrition promotes the establishment, survival, and fecundity of these parasites, but the magnitude of the effect depends on factors such as host species, parasite species, particular infection protocol used, magnitude of the infection, severity of the nutritional deficiency, and presence of single or multiple infections and single or multiple nutritional deficiencies. We highlight the Th2 arm of the immune system as a component of primary importance in the association between malnutrition and GI nematode infections. We summarize what is known about underlying mechanisms that may account for the observed patterns. Finally, we suggest future research directions.