Mu-Xin Chen

Rapid identification and differentiation of Fasciola hepatica and Fasciola gigantica by a loop-mediated isothermal amplification (LAMP) assay

The present study developed and validated a species-specific loop-mediated isothermal amplification (LAMP) assay for the rapid detection and discrimination of Fasciola hepatica and Fasciola gigantica. The LAMP assay is inexpensive, easy to perform and shows rapid reaction, wherein the amplification can be obtained in 45 min under isothermal conditions of 61 °C or 62 °C by employing a set of four species-specific primer mixtures and results can be checked through naked-eye visualization. The optimal assay conditions with no cross-reaction with other closely related trematodes (Clonorchis sinensis, Opisthorchis viverrini, Orientobilharzia turkestanicum and Schistosoma japonicum) as well as within the two Fasciola species were established. The assay was validated by examining F. gigantica DNA in the intermediate host snails and in faecal samples. The results indicated that the LAMP assay is approximately 10(4) times more sensitive than the conventional specific PCR assays. These findings indicate that this Fasciola species-specific LAMP assay may have a potential clinical application for detection and differentiation of Fasciola species, especially in endemic countries.

Comparative Characterization of MicroRNAs from the Liver Flukes Fasciola gigantica and F. hepatica

MicroRNAs (miRNAs) are key regulators of gene expression at the post-transcription level. The present study specifically explored and compared the miRNA expression profiles of F. gigantica and F. hepatica using an integrated sequencing and bioinformatics platform and quantitative real-time PCR. Nineteen and 16 miRNA candidates were identified from F. gigantica and F. hepatica, respectively. The two parasites shared 11 miRNAs, with 8 also showing similarity to miRNAs of Schistosoma japonicum. Another 8 miRNAs were identified as F. gigantica-specific and 5 as F. hepatica-specific, most of which were novel. Predicted target analysis with 11465 mRNA and EST sequences of F. hepatica and F. gigantica revealed that all of the miRNAs had more than one target, ranging from 2 to 398 with an average of 51 targets. Some functions of the predicted targets were only found in F. gigantica, such as “transcription regulator”, while some others were only found in F. hepatica, such as “reproduction” and “response to stimulus”, indicating the different metabolism and gene regulation patterns of the two parasites. The present study represents the first global comparative characterization of miRNA expression profiles of F. gigantica and F. hepatica, which has provided novel valuable resources for a better understanding of the two zoonotic trematodes.

Development of a TaqMan based real-time PCR assay for detection of Clonorchis sinensis DNA in human stool samples and fishes

Clonorchiasis caused by the oriental liver fluke Clonorchis sinensis is a fish-borne zoonosis endemic in a number of countries. This article describes the development of a TaqMan based real-time PCR assay for detection of C. sinensis DNA in human feces and in fishes. Primers targeting the first internal transcribed spacer (ITS-1) sequence of the fluke were highly specific for C. sinensis, as evidenced by the negative amplification of closely related trematodes in the test with the exception of Opisthorchis viverrini. The detection limit of the assay was 1pg of purified genomic DNA, 5EPG (eggs per gram feces) or one metacercaria per gram fish filet. The assay was evaluated by testing 22 human fecal samples and 37 fish tissues microscopically determined beforehand, and the PCR results were highly in agreement with the microscopic results. This real-time PCR assay provides a useful tool for the sensitive detection of C. sinensis DNA in human stool and aquatic samples in China and other endemic countries where O. viverrini and Opisthorchis felineus are absent.

Enzootic angiostrongyliasis in Shenzhen, China.

To the Editor: Angiostrongylus cantonensis is a zoonotic parasite that causes eosinophilic meningitis in humans after they ingest infective larvae in freshwater and terrestrial snails and slugs, paratenic hosts (such as freshwater fish, shrimps, frogs, and crabs), or contaminated vegetables. With the increase of income and living standards, and the pursuit of exotic and delicate foods, populations around the world have seen angiostrongyliasis become an important foodborne parasitic zoonosis (1–9). Shenzhen municipality is situated in the most southern part of mainland People’s Republic of China between the northern latitudes of 22°27′ to 22°52′ and eastern longitudes of 113°46′ to 114°37′; it shares a border with the Hong Kong Special Administrative Region, China, in the south. The climate is subtropical, with an average annual temperature of 23.7°C. The city is 1,952.84 km2 and has a population of 10 million. Since 2006, thirty-two sporadic cases of human eosinophilic meningitis caused by consumption of undercooked aquacultured snails have been documented in Shenzhen (Shenzhen Center for Disease Control and Prevention, unpub. data). To identify the source of these infections and assess the risk for an outbreak of eosinophilic meningitis, we conducted a survey to investigate whether A. cantonensis occurs in wild rats and snails in Shenzhen. To examine A. cantonensis infection in intermediate host snails, 302 terrestrial snails (Achatina fulica) were collected from 10 investigation sites across Shenzhen, and 314 freshwater snails (Pomacea canaliculata)were sampled from 6 investigation sites. We examined the snails for A. cantonensis larvae by using pepsin digestion standardized procedures (3). To survey the prevalence of adult A. cantonensis in definitive host rats, we collected 187 Rattus norvegicus rats and 121 R. flavipectus rats collected from 4 sites where positive snails positive for A. cantonensis were found. These rats were examined for the presence of adult A. cantonensis in their cardiopulmonary systems. A. cantonensis larvae were found in 96 (15.6%) of 616 examined snails. Of these, P. canaliculata had an average infection rate of 20.7% (65/314), significantly higher (p<0.01) than that of A. fulica (10.3%, 31/302), an indication that P. canaliculata may be the principal intermediate host for A. cantonensis in Shenzhen. A. cantonensis adults were recovered from the cardiopulmonary systems of 37 (12%) of 308 examined rats. Infection rate for R. norvegicus rats was 16.6% (31/187), significantly higher (p<0.01) than that for R. flavipectus (4.9%, 6/121), an indication that R. norvegicus may be the principal definitive host for A. cantonensis in Shenzhen, possibly due to the rat’s preference for eating snails. Infection rates were higher for female rats (25.6% for R. norvegicus and 7.8% for R. flavipectus) than for male rats (8.9% for R. norvegicus, 2.9% for R. flavipectus), possibly because female rats eat more snails to supply proteins for reproduction. This report of enzootic A. cantonensis infection in wild rats and snails in Shenzhen demonstrates the existence of natural origins of infection with A. cantonensis for humans in this city. Persons in Shenzhen eat raw or undercooked freshwater and terrestrial snails and slugs. This practice provides opportunities for infection with A. cantonensis, particularly given that P. canaliculata has been aquacultured intensively for human consumption. The prevalence of A. cantonensis in wild rats and snails in Shenzhen poses substantial risk for future outbreaks of human eosinophilic meningitis. Moreover, public health officials, epidemiologists, researchers, clinical technicians, medical practitioners, parasitologists, and veterinarians, as well as the general public, should be aware of such risks, and integrated strategies should be taken to reduce or eliminate such risks.

Identification and characterization of microRNAs in Trichinella spiralis by comparison with Brugia malayi and Caenorhabditis elegans.

Trichinella spiralis is an important zoonotic nematode causing trichinellosis which is associated with human diseases such as malaise, anorexia, nausea, vomiting, abdominal pain, fever, diarrhea, and constipation. microRNAs (miRNAs) are endogenous small non-coding RNAs that play important roles in the regulation of gene expression. The objective of the present study was to examine the miRNA expression profile of the larvae of T. spiralis by Solexa deep sequencing combined with stem-loop real-time polymerase chain reaction (PCR) analysis. T. spiralis larvae were collected from the skeletal muscle of naturally infected pigs in Henan province, China, by artificial digestion using pepsin. The specific identity of the T. spiralis larvae was confirmed by PCR amplification and subsequent sequence analysis of the internal transcribed spacer of ribosomal DNA. A total of 17,851,693 reads with 2,773,254 unique reads were obtained. Eleven conserved miRNAs from 115 unique xsmall RNAs (sRNAs) and 12 conserved miRNAs from 130 unique sRNAs were found by BLAST analysis against the known miRNAs of Caenorhabditis elegans (ftp://ftp.ncbi.nih.gov/genomes/Caenorhabditis_elegans) and Brugia malayi dataset (http://www.ncbi.nlm.nih.gov/genomeprj?Db=genomeprj&cmd=ShowDetailView&TermToSearch=9549) in miRBase, respectively. One novel miRNA with 12 precursors were identified and certified using the reference genome of B. malayi, while no novel miRNA was found when using the reference genome of C. elegans. Nucleotide bias analysis showed that the uracil was the prominent nucleotide, particularly at the 1st, 6th, 18th, and 23th positions, which were almost at the beginning, middle, and the end of the conserved miRNAs. The identification and characterization of T. spiralis miRNAs provides a new resource to study regulation of genes and their networks in T. spiralis.

Chicken egg yolk antibodies (IgY) for detecting circulating antigens of Schistosoma japonicum.

BACKGROUND IgY isolated from egg yolk has been widely used in immunodiagnostic tests, including tests to detect circulating antigen (soluble egg antigen or SEA) of Schistosoma japonicum. RESULTS A sandwich ELISA was established using a combination of anti-S. japonicum SEA-IgY polyclonal antibodies and IgM monoclonal antibodies. To explore sensitivity and specificity of the sandwich ELISA, serum samples from 43 patients infected with S. japonicum were tested. All acute cases and 91.3% of the chronic cases showed a positive reaction. Only 5% of the control sera from healthy persons gave a positive response. Cross-reactions with antibodies to nine other parasites were rare. CONCLUSION The developed immunoassay is reasonably sensitive and specific. It could be used for field research and treatment efficacy assessments.

Genetic diversity and relatedness of Fasciola spp. isolates from different hosts and geographic regions revealed by analysis of mitochondrial DNA sequences.

The present study examined sequence variability in a portion of the mitochondrial cytochrome c oxidase subunit 1 (pcox1) and NADH dehydrogenase subunits 4 and 5 (pnad4 and pnad5) among 39 isolates of Fasciola spp., from different hosts from China, Niger, France, the United States of America, and Spain; and their phylogenetic relationships were re-constructed. Intra-species sequence variations were 0.0-1.1% for pcox1, 0.0-2.7% for pnad4, and 0.0-3.3% for pnad5 for Fasciola hepatica; 0.0-1.8% for pcox1, 0.0-2.5% for pnad4, and 0.0-4.2% for pnad5 for Fasciola gigantica, and 0.0-0.9% for pcox1, 0.0-0.2% for pnad4, and 0.0-1.1% for pnad5 for the intermediate Fasciola form. Whereas, nucleotide differences were 2.1-2.7% for pcox1, 3.1-3.3% for pnad4, and 4.2-4.8% for pnad5 between F. hepatica and F. gigantica; were 1.3-1.5% for pcox1, 2.1-2.9% for pnad4, 3.1-3.4% for pnad5 between F. hepatica and the intermediate form; and were 0.9-1.1% for pcox1, 1.4-1.8% for pnad4, 2.2-2.4% for pnad5 between F. gigantica and the intermediate form. Phylogenetic analysis based on the combined sequences of pcox1, pnad4 and pnad5 revealed distinct groupings of isolates of F. hepatica, F. gigantica, or the intermediate Fasciola form irrespective of their origin, demonstrating the usefulness of the mtDNA sequences for the delineation of Fasciola species, and reinforcing the genetic evidence for the existence of the intermediate Fasciola form.

Monoclonal antibodies against excretory/secretory antigens of Angiostrongylus cantonensis.

In the present study, four murine monoclonal antibodies (MAbs) were generated against the excretory/secretory (ES) products of Angiostrongylus cantonensis adult worms; two represented IgG1 and two represented IgM MAbs, and they were designated 12D5, 15F8, 21B7 and 14G10, respectively. Immunoblotting revealed that all of the MAbs predominantly recognized a 98 kDa antigen in the ES products of A. cantonensis adult worms, and no cross reactions were found with the whole worm antigens of some other common parasites, namely, Schistosoma japonicum, Clonorchis sinensis, Paragonimus westermani, Ascaris lumbricoides, Trichinella spiralis, Anisakis sp., Echinococcus granulosus, Taenia solium, and Spirometra erinacei. Immunolocalization showed that all of the four MAbs reacted with the cuticle of the adult parasite, the external surface of its intestinal canal and reproductive organs, and its egg and first-stage larvae in the lungs of rats experimentally infected with A. cantonensis. The generation and characterization of four specific MAbs against A. cantonensis ES antigens provide foundation for the development of specific immunological diagnostic techniques for human infections with A. cantonensis.

A Protein Microarray for the Rapid Screening of Patients Suspected of Infection with Various Food-Borne Helminthiases

Background Food-borne helminthiases (FBHs) have become increasingly important due to frequent occurrence and worldwide distribution. There is increasing demand for developing more sensitive, high-throughput techniques for the simultaneous detection of multiple parasitic diseases due to limitations in differential clinical diagnosis of FBHs with similar symptoms. These infections are difficult to diagnose correctly by conventional diagnostic approaches including serological approaches. Methodology/Principal Findings In this study, antigens obtained from 5 parasite species, namely Cysticercus cellulosae, Angiostrongylus cantonensis, Paragonimus westermani, Trichinella spiralis and Spirometra sp., were semi-purified after immunoblotting. Sera from 365 human cases of helminthiasis and 80 healthy individuals were assayed with semi-purified antigens by both a protein microarray and the enzyme-linked immunosorbent assay (ELISA). The sensitivity, specificity and simplicity of each test for the end-user were evaluated. The specificity of the tests ranged from 97.0% (95% confidence interval (CI): 95.3–98.7%) to 100.0% (95% CI: 100.0%) in the protein microarray and from 97.7% (95% CI: 96.2–99.2%) to 100.0% (95% CI: 100.0%) in ELISA. The sensitivity varied from 85.7% (95% CI: 75.1–96.3%) to 92.1% (95% CI: 83.5–100.0%) in the protein microarray, while the corresponding values for ELISA were 82.0% (95% CI: 71.4–92.6%) to 92.1% (95% CI: 83.5–100.0%). Furthermore, the Youden index spanned from 0.83 to 0.92 in the protein microarray and from 0.80 to 0.92 in ELISA. For each parasite, the Youden index from the protein microarray was often slightly higher than the one from ELISA even though the same antigen was used. Conclusions/Significance The protein microarray platform is a convenient, versatile, high-throughput method that can easily be adapted to massive FBH screening.

DEVELOPMENT OF A DOUBLE ANTIBODY SANDWICH ELISA ASSAY FOR THE DIAGNOSIS OF ANGIOSTRONGYLIASIS

abstract:  With the use of 2 monoclonal antibodies (MAbs) against excretory/secretory (ES) antigens of adult Angiostrongylus cantonensis, a new method was developed for double antibody sandwich ELISA for the detection of circulating antigens (CAg). To evaluate the sensitivity of the new procedure, the CAg in sera of rats (80) and mice (15) infected with A. cantonensis, as well as CAg in sera of clinically confirmed angiostrongyliasis patients (70), were evaluated. Cross-reaction testing was used to determine the specificity of serum from patients infected with Ascaris lumbricoides, Trichinella spiralis, Toxoplasma gondii, Schistosoma japonicum, Paragonimus westermani, Clonorchis sinensis, Echinococcus granulosus, Spirometra, and Taenia solium, as well as normal healthy people. The results proved that the sensitivity and the specificity of the new method were totally effective for the detection of A. cantonensis CAg. The assay is highly sensitive, specific, and reproducible, with easy handling and excellent cost effectiveness, and thereby provides a new method for the accurate diagnosis of angiostrongyliasis.