Detection of Opisthorchis viverrini in infected bithynid snails by real-time fluorescence resonance energy transfer PCR-based method and melting curve analysis

Clonorchiasis and opisthorchiasis: epidemiology, transmission, clinical features, morbidity, diagnosis, treatment, and control

Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are important liver flukes that cause a considerable public health burden in eastern Asia, southeastern Asia, and eastern Europe, respectively. The life cycles are complex, involving humans, animal reservoirs, and two kinds of intermediate hosts. An interplay of biological, cultural, ecological, economic, and social factors drives transmission. Chronic infections are associated with liver and biliary complications, most importantly cholangiocarcinoma. With regard to diagnosis, stool microscopy is widely used in epidemiologic surveys and for individual diagnosis. Immunologic techniques are employed for screening purposes, and molecular techniques facilitate species differentiation in reference laboratories. The mainstay of control is preventive chemotherapy with praziquantel, usually combined with behavioral change through information, education and communication, and environmental control. Tribendimidine, a drug registered in the People's Republic of China for soil-transmitted helminth infections, shows potential against both C. sinensis and O. viverrini and, hence, warrants further clinical development. Novel control approaches include fish vaccine and biological control. Considerable advances have been made using multi-omics which may trigger the development of new interventions. Pressing research needs include mapping the current distribution, disentangling the transmission, accurately estimating the disease burden, and developing new diagnostic and treatment tools, which would aid to optimize control and elimination measures.

Odds, challenges and new approaches in the control of helminthiasis, an Asian study

The time is passing, and the worms are still a major struggle for local people in Asian countries, especially the less empowered and in a situation of social vulnerability. We are working in the field in Laos, Thailand, and the Philippines where the usual control programs based only on human treatment are partially effective. Areas with mass drug administration could diminish, but not eliminate STHs of endemic areas. The persistence of helminthic NTDs in the environment and animal hosts makes the eradication a very difficult task. Great changes in the landscapes of endemic areas, such as construction of dams, can change the fauna and the lifestyle of local people. Those changes can improve infrastructure, but it can also lead to social vulnerability. The challenge, then, is to conceive new and directed control programs for helminthiasis based on multi- and transdisciplinary approaches diminishing the health gap in a globalized world. In this short review, we summarize the actual scenario concerning the main helminths in Southeast Asia and how an environmental DNA approach and the use of GIS could contribute to surveillance and control programs.

Molecular Epidemiology of Anisakis and Anisakiasis: An Ecological and Evolutionary Road Map

This review addresses the biodiversity, biology, distribution, ecology, epidemiology, and consumer health significance of the so far known species of Anisakis, both in their natural hosts and in human accidental host populations, worldwide. These key aspects of the Anisakis species' biology are highlighted, since we consider them as main driving forces behind which most of the research in this field has been carried out over the past decade. From a public health perspective, the human disease caused by Anisakis species (anisakiasis) appears to be considerably underreported and underestimated in many countries or regions around the globe. Indeed, when considering the importance of marine fish species as part of the everyday diet in many coastal communities around the globe, there still exist significant knowledge gaps as to local epidemiological and ecological drivers of the transmission of Anisakis spp. to humans. We further identify some key knowledge gaps related to Anisakis species epidemiology in both natural and accidental hosts, to be filled in light of new 'omic' technologies yet to be fully developed. Moreover, we suggest that future Anisakis research takes a 'holistic' approach by integrating genetic, ecological, immunobiological, and environmental factors, thus allowing proper assessment of the epidemiology of Anisakis spp. in their natural hosts, in human populations, and in the marine ecosystem, in both space and time.

Application of environmental DNA analysis for the detection of Opisthorchis viverrini DNA in water samples

Opisthorchiasis, which can lead to cholangiocarcinoma in cases of chronic infection, is a major public health problem in Southeast Asian countries. The trematode, Opisthorchis viverrini, is the causative agent of the disease. Accurate and rapid monitoring of O. viverrini is crucial for disease prevention and containment. Therefore, in this study we sought to develop a novel species-specific real-time PCR assay for detecting O. viverrini using environmental DNA (eDNA). The diagnostic sensitivity of the newly developed real-time PCR assay was similar to that of the traditional PCR assay for 50 fecal samples collected in Lao PDR (21 and 19 samples were positive by real-time PCR and traditional PCR, respectively). The efficacy of eDNA analysis and its applicability in the field were tested using a total of 94 environmental water samples collected from 44 sites in Savannakhet, Lao PDR during May and October 2015 and February 2016. O. viverrini eDNA was detected in five samples by real-time PCR, indicating the presence of the fluke in the area and the risk of infection for individuals consuming fish from these water sources. The application of eDNA analysis would facilitate the identification of O. viverrini endemic hotspots and contribute to the ecological control of opisthorchiasis, and this strategy can be applied to other eukaryotic water pathogens.

Prevalence of gastrointestinal helminth parasites of zoonotic significance in dogs and cats in lower Northern Thailand

Gastrointestinal zoonotic helminths of dogs and cats have a public health concern worldwide. We investigated the prevalence of gastrointestinal helminths of zoonotic significance in dogs and cats in lower Northern Thailand and utilized molecular tools for species identification of hookworms and Opisthorchis viverrini. Fecal samples of 197 dogs and 180 cats were collected. Overall prevalence of infection using microscopy was 40.1% in dogs and 33.9% in cats. Helminth infection found in both dogs and cats included hookworms, Spirometra spp., Taenia spp., Toxocara spp., O. viverrini, Strongyloides spp. and Trichuris spp. Hookworms were the most common helminth in dogs, while Spirometra spp. were the most prevalent in cats. Among hookworm infection in dogs and cats, Ancylostoma ceylanicum was the most prevalent hookworm, being 82.1% in hookworm infected dogs and 95.8% in hookworm infected cats. Mixed-infection due to hookworms and Spirometra spp. was the most dominant in both dogs and cats. Our finding showed that zoonotic helminth infection is highly prevalent in dogs and cats in the lower Northern area of Thailand.

Molecular detection of Schistosoma japonicum in infected snails and mouse faeces using a real-time PCR assay with FRET hybridisation probes

A real-time polymerase chain reaction (PCR) assay with fluorescence resonance energy transfer (FRET) hybridisation probes combined with melting curve analysis was developed to detect Schistosoma japonicum in experimentally infected snails and in faecal samples of infected mice. This procedure is based on melting curve analysis of a hybrid between an amplicon from the S. japonicum internal transcribed spacer region 2 sequence, which is a 192-bp S. japonicum-specific sequence, and fluorophore-labelled specific probes. Real-time FRET PCR could detect as little as a single cercaria artificially introduced into a pool of 10 non-infected snails and a single egg inoculated in 100 mg of non-infected mouse faeces. All S. japonicum-infected snails and all faecal samples from infected mice were positive. Non-infected snails, non-infected mouse faeces and genomic DNA from other parasites were negative. This assay is rapid and has potential for epidemiological S. japonicum surveys in snails, intermediate hosts and faecal samples of final hosts.

Rapid detection and differentiation of Clonorchis sinensis and Opisthorchis viverrini eggs in human fecal samples using a duplex real-time fluorescence resonance energy transfer PCR and melting curve analysis

We developed a single step duplex real-time fluorescence resonance energy transfer (FRET) PCR merged with melting curve analysis for the fast detection and differentiation of Clonorchis sinensis and Opisthorchis viverrini eggs in human fecal samples. Two species of mitochondrial NADH dehydrogenase subunit 2 (nad2) DNA elements, the 165-bp nad2 product of C. sinensis and the 209-bp nad2 product of O. viverrini, were amplified by species-specific primers, and the fluorescence melting curve analyses were generated from hybrid of amplicons and two pairs of species-specific fluorophore-labeled probes. By their different fluorescence channels and melting temperatures, both C. sinensis and O. viverrini eggs in infected human fecal samples were detected and differentiated with high (100%) sensitivity and specificity. Detection limit was as little as a single C. sinensis egg and two O. viverrini eggs in 100 mg of fecal sample. The assay could distinguish the DNA of both parasites from the DNA of negative fecal samples and fecal samples with other parasitosis, as well as from the well-defined genomic DNA of human leukocytes and other parasites. It can reduce labor time of microscopic examination and is not prone to carry over contamination of agarose electrophoresis. Our duplex real-time FRET PCR method would be useful to determine the accurate range of endemic areas and/or to discover the co-endemic areas of two liver flukes, C. sinensis and O. viverrini, in Asia. This method also would be helpful for the differential diagnosis of the suspected cases of liver fluke infections among travelers who had visited the endemic countries of those parasites.

Molecular evidence of Opisthorchis viverrini in infected bithyniid snails in the Lao People's Democratic Republic by specific hybridization probe-based real-time fluorescence resonance energy transfer PCR method

Naturally occurring bithyniid snails, Bithynia siamensis goniomphalos (Prosobranchia: Bithyniidae), and their intermediate hosts were sampled from Khammouane Province, the Lao People's Democratic Republic, and the prevalence of the carcinogenic human liver fluke, Opisthorchis viverrini, was examined. The presence of O. viverrini cercariae in snails was examined by cercarial shedding test and then confirmed by specific hybridization probe-based real-time fluorescence resonance energy transfer (FRET) PCR method. The real-time FRET PCR method is based on a fluorescence melting curve analysis of a hybrid between an amplicon produced from the pOV-A6 specific sequence (Genbank accession no. S80278), a 162-bp repeated sequence specific to O. viverrini, and specific fluorophore-labeled probes. Mean melting temperature of O. viverrini DNA from the cercariae and each of two positive snails by shedding test was 66.3 ± 0.1. The O. viverrini infection rate in snails was 2.47% (2/81) by cercarial shedding test but was 8.52% (4/47) by real-time FRET PCR method. The real-time FRET PCR method is rapid and effective in examining a large number of snail samples simultaneously. Validation using molecular evidence from this procedure provides another tool for surveying the prevalence of O. viverrini-infected snails in Southeast Asian countries.