[Establishment and preliminary application of a recombinase-aided isothermal amplification assay-based multiplex nucleic acid assay for detection of three Echinococcus species]

OBJECTIVE

To establish a multiplex nucleic acid assay for rapid detection of Echinococcus multilocularis, E. granulosus and E. shiquicus based on the recombinase-aided isothermal amplification assay (RAA) and to preliminarily assess its diagnostic efficiency.

METHODS

The mitochondrial genomic sequences of E. multilocularis (GenBank accession number: NC_000928), E. granulosus (GenBank accession number: NC_044548) and E. shiquicus (GenBank accession number: NC_009460) were used as target sequences, and three pairs of primers were designed based on the RAA primer design principle and synthesized for the subsequent multiple RAA amplification. The genomic DNA of E. multilocularis, E. granulosus and E. shiquicus at different concentrations and the recombinant plasmids containing the target gene at various concentrations were amplified to evaluate the diagnostic sensitivity of the multiplex RAA assay, and the genomic DNA of E. multilocularis, E. granulosus, E. shiquicus, Taenia multiceps, T. saginata, T. asiatica, Dipylidium caninum, T. hydatigena, Toxocara canis, Fasciola hepatica, T. pisiformis, Mesocestoides lineatus and Cryptosporidiumn canis was detected using the multiplex RAA assay to evaluate its specificity. In addition, the reaction condition of the multiplex RAA assay was optimized, and was then employed to detect the tissues with echinococcosis lesions, simulated canine fecal samples and field captured fox fecal samples to examine its application values.

RESULTS

The multiplex RAA assay was effective to specifically amplify the mitochondrial gene fragments of E. multilocularis, E. granulosus and E. shiquicus within 40 min at 39 °C, with sequence lengths of 540, 430 bp and 200 bp, respectively. This multiplex RAA assay showed the minimum detection limits of 2.0, 2.5 pg/μL and 3.1 pg/μL for detection of the genomic DNA of E. multilocularis, E. granulosus and E. shiquicus, and presented the minimum detection limit of 200 copies/μL for detection of the recombinant plasmids containing E. multilocularis, E. granulosus and E. shiquicus target genes. This multiplex RAA assay was effective to simultaneously detect single and multiple infections with E. multilocularis, E. granulosus and E. shiquicus, but failed to amplify the genomic DNA of T. multiceps, T. saginata, T. asiatica, D. caninum, T. hydatigena, T. canis, F. hepatica, T. pisiformis, M. lineatus and C. canis. In addition, the optimized multiplex RAA assay was effective to detect all positive samples from the tissue samples with echinococcosis lesions, simulated canine fecal samples and field captured fox fecal samples, which was fully consistent with the detection of the single PCR assay.

CONCLUSIONS

A sensitive and specific multiplex nucleic acid assay for rapid detection of E. multilocularis, E. granulosus and E. shiquicus has been successfully established.

An epidemiological survey of echinococcosis in intermediate and definitive hosts in Qinghai Province, China

In order to understand the epidemiological status of alveolar and cystic echinococcosis in intermediate and definitive hosts in Qinghai Province, China, during the period 2007-2011, we investigated the infection in humans and animals, including yaks, Tibetan sheep, Tibetan dogs, and wild foxes distributed in different counties around the province. Sera from local residents were examined using a rapid serodiagnostic kit to detect specific antibodies against Echinococcus. Seropositive samples were confirmed with B-scan ultrasonography and X-ray examinations. Yaks and Tibetan sheep were checked at slaughterhouses, and cysts and suspicious lesions were collected for analysis. A rapid diagnostic strip was used to detect Echinococcus adults in Tibetan dogs. Positive dogs were dewormed and the parasites collected. Wild foxes were trapped and necropsies performed with particular attention to the intestine. Forty-eight of 735 (6.4%) humans tested were positive and 475 of 854 (55.6%) Tibetan sheep and 85 of 352 (24.15%) yaks were infected with Echinococcus. Across different counties, 214 of 948 (22.57%) Tibetan dogs were positive, and five of 36 (13.9%) wild foxes were infected with Echinococcus. Molecular studies showed that all the infections detected in humans, domestic yaks, and Tibetan sheep were the G1 genotype (E. granulosus), whereas the parasites from Tibetan foxes and Tibetan dogs were E. shiquicus and E. multilocularis, respectively. In conclusion, Echinococcosis is hyperendemic in Qinghai Province in both its intermediate and definitive hosts and the G1 genotype of cystic Echinococcus is the dominant strain.