Performance of Mini Parasep® SF stool concentrator kit, Kato-Katz, and formalin-ethyl acetate concentration methods for diagnosis of opisthorchiasis in Northeast Thailand

Study of the population genetic structure of Opisthorchis-like eggs in northern Thailand using mitochondrial genes

BACKGROUND

Opisthorchis-like eggs are a public health problem in northern and northeastern Thailand. However, the genetic epidemiology and structure of these parasites in northern Thailand are unknown. Thus, this study investigated their population genetic structure using cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) nucleotide sequences.

METHODOLOGY/PRINCIPAL FINDINGS

A study was conducted in the hill tribe regions of Chiang Mai Province, northern Thailand. Internal transcribed spacer 2 polymerase chain reaction and restriction fragment length polymorphism were used to distinguish 205 positive feces samples for Opisthorchis-like eggs. The results showed that the prevalence of O. viverrini and Haplorchis taichui was 10.5% and 38.2%, respectively, and the co-infection rate was 37.2%. To determine the genetic structure of O. viverrini and H. taichui using cox1 and nad1 genes, genetic analysis was performed using 30 randomly chosen fecal samples for Opisthorchis-like eggs. Pairwise FST analysis indicated that O. viverrini and H. taichui displayed nonsignificant genetic differentiation within Chiang Mai Province and between interpopulations from different geographic areas. Moreover, within the intrapopulation in Chiang Mai Province, cox1 presented higher gene flow than nad1 in O. viverrini, while nad1 demonstrated higher gene flow than cox1 in H. taichui. The neutrality tests based on Fu's Fs indicated population expansion and selective sweep from bottleneck or hitchhiking in O. viverrini and H. taichui populations, supported by haplotype network patterns. Phylogenetic tree analysis based on cox1 and nad1 revealed the monophyly of O. viverrini and H. taichui and genetic relationships with other isolates collected from Thailand, Lao People's Democratic Republic (PDR), and Vietnam.

CONCLUSIONS/SIGNIFICANCE

This study investigated the molecular discrimination and genetic structure of Opisthorchis-like eggs in northern Thailand. The genetic information derived from this study could be associated with the background, molecular epidemiology, and disease severity of these parasites.

Prevalence of opisthorchiid and other endoparasitic infections among cats and dogs in Novosibirsk oblast (Western Siberia, Russia)

To determine the current reservoir status and prevalence of Opisthorchis felineus infection in opisthorchiosis-endemic areas, feces samples were collected from 103 cats and 101 dogs admitted to shelters or discount sterilization centers from various districts of Novosibirsk city and from villages and towns along the Ob River (Novosibirsk Oblast). The feces samples were evaluated using two methods simultaneously: the formalin-ether sedimentation assay and a modified flotation assay. The prevalence of opisthorchiid infection was higher among cats (12.6%; 95% confidence interval 6.9-20.6%) than among dogs (4.0%; 95% confidence interval 1.1-9.8%). Overall prevalence of endoparasites among cats was 42.7% (five helminthic and four protozoan species) and among dogs 51.5% (eight helminthic and five protozoan species). Among the parasites found in the dogs, the prevalence of Sarcocystis sp. was the highest (16.8%), and in cats, the highest prevalence was shown by Giardia sp. and Toxocara cati (14.6% for each species). These results confirm the considerable contribution of stray cats and dogs to the maintenance of opisthorchiid eggs in the environment; these data should be taken into account for the development of effective control and education programs.

Production and immunological characterization of the novel single-chain variable fragment (scFv) antibodies against the epitopes on Opisthorchis viverrini cathepsin F (OvCatF)

BACKGROUND

Opisthorchis viverrini infection is a significant health problem in several countries, especially Southeast Asia. The infection causes acute gastro-hepatic symptoms and also long-term infection leading to carcinogenesis of an aggressive bile duct cancer (cholangiocarcinoma; CCA). Hence, the early diagnosis of O. viverrini infection could be the way out of this situation. Still, stool examination by microscopic-based methods, the current diagnostic procedure is restricted by low parasite egg numbers in the specimen and unprofessional laboratorians. The immunological procedure provides a better chance for diagnosis of the infection. Hence, this study aims to produce single-chain variable fragment (scFv) antibodies for use as a diagnostic tool for O. viverrini infection.

METHODS

This study uses phage display technologies to develop the scFv antibodies against O. viverrini cathepsin F (OvCatF). The OvCatF-deduced amino acid sequence was analyzed and predicted for B-cell epitopes used for short peptide synthesis. The synthetic peptides were used to screen the phage library simultaneously with OvCatF recombinant protein (rOvCatF). The potentiated phages were collected, rescued, and reassembled in XL1-blue Escherichia coli (E. coli) as a propagative host. The positive clones of phagemids were isolated, and the single-chain variable (scFv) fragments were sequenced, computationally predicted, and molecular docked. The complete scFv fragments were digested from the phagemid, subcloned into the pOPE101 expression vector, and expressed in XL1-blue E. coli. Indirect ELISA and Western analysis were used to verify the detection efficiency.

RESULTS

The scFv phages specific to OvCatF were successfully isolated, subcloned, and produced as a recombinant protein. The recombinant scFv antibodies were purified and refolded to make functional scFv. The evaluation of specific recognition of the particular epitopes and detection limit results by both computational and laboratory performances demonstrated that all three recombinant scFv antibodies against OvCatF could bind specifically to rOvCatF, and the lowest detection concentration in this study was only one hundred nanograms.

CONCLUSION

Our produced scFv antibodies will be the potential candidates for developing a practical diagnostic procedure for O. viverrini infection in humans in the future.

Prevalence estimates of Opisthorchis viverrini and Clonorchis sinensis infection in the Greater Mekong subregion: a systematic review and meta-analysis

BACKGROUND

Opisthorchiasis and clonorchiasis, caused by Opisthorchis viverrini and Clonorchis sinensis, respectively, are significant yet neglected foodborne trematodiases in the Great Mekong Subregion (GMS). Despite the reporting of the prevalence of these human liver flukes in the region over the past decades, there has been a lack of a comprehensive and systematic consolidation of this data. Therefore, we aimed to conduct a thorough systematic review and meta-analysis to synthesize and analyze time-trend prevalence estimates of both O. viverrini and C. sinensis across the GMS for the past 30 years.

METHODS

This study undertakes a systematic review using a comprehensive search for published articles in PubMed, EMBASE, Scopus, Cochrane and Thai Journal Online databases until early 2023. The pooled prevalence of O. viverrini and C. sinensis infection was analyzed through a random-effects meta-analysis, with meta-regression analysis used to quantify associations with study characteristics. Sub-group analysis was conducted, whenever comparison data were available, to assess the risk of O. viverrini and C. sinensis infection in each GMS country. Heterogeneity among studies was assessed using the Q statistic and quantified by using the I 2 Index.

RESULTS

From a total of 2997 articles, 155 articles comprising 218 datasets and 751,108 participants were included for review. The GMS prevalence of O. viverrini was 21.11% [45,083/260,237; 95% confidence interval (CI): 17.74-24.47%]. Pooled prevalence estimates were highly observed in Laos (34.06%, 95% CI: 26.85-41.26%), followed by Thailand (18.19%, 95% CI: 13.86-22.51%), and Cambodia (10.48%, 95% CI: 5.52-15.45%). Myanmar and Vietnam had limited data sources for calculation. Clonorchis sinensis infection in GMS was 25.33% (95% CI: 18.32-32.34%), with Guangxi, China, exhibiting the highest prevalence rates at 26.89% (95% CI: 18.34-35.43%), while Vietnam had a prevalence rate of 20.30% (95% CI: 9.13-31.47%). O. viverrini prevalence decreased significantly over time, whereas C. sinensis infection appeared to be stable consistently over time in both China and Vietnam.

CONCLUSIONS

This comprehensive study, drawing from the largest datasets to date, offers an in-depth systematic prevalence review of human liver flukes in the Greater Mekong Subregion. It underscores the imperative for systematic surveillance, data collection, and the implementation of intervention and control measures for these infectious diseases of poverty.

Multi-epitope protein production and its application in the diagnosis of opisthorchiasis

BACKGROUND

Opisthorchiasis and cholangiocarcinoma (CCA) continue to be public health concerns in many Southeast Asian countries. Although the prevalence of opisthorchiasis is declining, reported cases tend to have a light-intensity infection. Therefore, early detection by using sensitive methods is necessary. Several sensitive methods have been developed to detect opisthorchiasis. The immunological detection of antigenic proteins has been proposed as a sensitive method for examining opisthorchiasis.

METHODS

The Opisthorchis viverrini antigenic proteins, including cathepsin B (OvCB), asparaginyl endopeptidase (OvAEP), and cathepsin F (OvCF), were used to construct multi-antigenic proteins. The protein sequences of OvCB, OvAEP, and OvCF, with a high probability of B cell epitopes, were selected using BepiPred 1.0 and the IEDB Analysis Resource. These protein fragments were combined to form OvCB_OvAEP_OvCF recombinant DNA, which was then used to produce a recombinant protein in Escherichia coli strain BL21(DE3). The potency of the recombinant protein as a diagnostic target for opisthorchiasis was assessed using immunoblotting and compared with that of the gold standard method, the modified formalin-ether concentration technique.

RESULTS

The recombinant OvCB_OvAEP_OvCF protein showed strong reactivity with total immunoglobulin G (IgG) antibodies against light-intensity O. viverrini infections in the endemic areas. Consequently, a high sensitivity (100%) for diagnosing opisthorchiasis was reported. However, cross-reactivity with sera from other helminth and protozoan infections (including taeniasis, strongyloidiasis, giardiasis, E. coli infection, enterobiasis, and mixed infection of Echinostome spp. and Taenia spp.) and no reactivity with sera from patients with non-parasitic infections led to a reduced specificity of 78.4%. In addition, the false negative rate (FNR), false positive rate (FPR), positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy were 0%, 21.6%, 81.4%, 100%, and 88.9%, respectively.

CONCLUSIONS

The high sensitivity of the recombinant OvCB_OvAEP_OvCF protein in detecting opisthorchiasis demonstrates its potential as an opisthorchiasis screening target. Nonetheless, research on reducing cross-reactivity should be undertaken by detecting other antibodies in other sample types, such as saliva, urine, and feces.

Misclassification of Opisthorchis viverrini and Minute Intestinal Fluke Eggs by Routine Laboratory Staff Using Images from the Kato-Katz Method

BACKGROUND

The Kato-Katz method is a commonly used diagnostic tool for helminth infections, particularly in field studies. This method can yield inaccurate results when samples contain eggs that are similar in appearance, such as Minute Intestinal Fluke (MIF) and Opisthorchis viverrini (OV) eggs. The close resemblance of eggs can be problematic and raises the possibility of false diagnoses. The objectives were to compare the diagnostic performance of the Kato-Katz method for accurately identifying MIF and OV and to provide evidence of possible misclassification.  Methods: Based on questionnaire responses from 15 (young parasitologists and public health staff), the test comprised 50 MIF egg images and 50 OV egg images, for a total of 100 Google Form questionnaires.

RESULTS

The morphology of MIF and OV eggs found size and shape similarity and found that the shoulder rims were small, while the OV egg found the knobs had disappeared. The opercular conjunction was apparent, the shoulder rims and miricidium were prominent. The average percentage of correctly classified infections was 61.6 ± 12.1%. The accuracy percentages for both public health staff and young parasitologists in identifying were found to be 59.0 ± 14.8 and 66.8 ± 2.8, respectively. There was no significant difference observed in both groups.

CONCLUSION

These findings highlight the need for improving the accuracy of parasite identification. Preserving stool samples before the Kato-Katz method can help mitigate the potential degradation or distortion of parasite eggs. The incorrect classification of both eggs had an impact on treatment plans and the policy of parasite control programs.

Ov-RPA-CRISPR/Cas12a assay for the detection of Opisthorchis viverrini infection in field-collected human feces

BACKGROUND

Opisthorchis viverrini infection is traditionally diagnosed using the Kato-Katz method and formalin ethyl-acetate concentration technique. However, the limited sensitivity and specificity of these techniques have prompted the exploration of various molecular approaches, such as conventional polymerase chain reaction (PCR) and real-time PCR, to detect O. viverrini infection. Recently, a novel technique known as recombinase polymerase amplification (RPA)-clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) (RPA-CRISPR/Cas) assay was developed as a point-of-care tool for the detection of various pathogens, including viruses and bacteria such as severe acute respiratory syndrome coronavirus 2 and Mycobacterium tuberculosis. This technology has demonstrated high sensitivity and specificity. Therefore, we developed and used the RPA-CRISPR/Cas assay to detect O. viverrini infection in field-collected human feces.

METHODS

To detect O. viverrini infection in fecal samples, we developed a CRISPR/Cas12a (RNA-guided endonuclease) system combined with RPA (Ov-RPA-CRISPR/Cas12a). Several fecal samples, both helminth-positive and helminth-negative, were used for the development and optimization of amplification conditions, CRISPR/Cas detection conditions, detection limits, and specificity of the RPA-CRISPR/Cas12a assay for detecting O. viverrini infection. The detection results were determined using a real-time PCR system based on fluorescence values. Additionally, as the reporter was labeled with fluorescein, the detection results were visually inspected using an ultraviolet (UV) transilluminator. A receiver operating characteristic curve (ROC) was used to determine the optimal cutoff value for fluorescence detection. The diagnostic performance, including sensitivity and specificity, of the Ov-RPA-CRISPR/Cas12a assay was evaluated on the basis of comparison with standard methods.

RESULTS

The Ov-RPA-CRISPR/Cas12a assay exhibited high specificity for detecting O. viverrini DNA. On the basis of the detection limit, the assay could detect O. viverrini DNA at concentrations as low as 10-1 ng using the real-time PCR system. However, in this method, visual inspection under UV light required a minimum concentration of 1 ng. To validate the Ov-RPA-CRISPR/Cas12a assay, 121 field-collected fecal samples were analyzed. Microscopic examination revealed that 29 samples were positive for O. viverrini-like eggs. Of these, 18 were confirmed as true positives on the basis of the Ov-RPA-CRISPR/Cas12a assay and microscopic examination, whereas 11 samples were determined as positive solely via microscopic examination, indicating the possibility of other minute intestinal fluke infections.

CONCLUSIONS

The Ov-RPA-CRISPR/Cas12a assay developed in this study can successfully detect O. viverrini infection in field-collected feces. Due to the high specificity of the assay reported in this study, it can be used as an alternative approach to confirm O. viverrini infection, marking an initial step in the development of point-of-care diagnosis.

Epidemiology and Geographical Distribution of Human Trematode Infections

Digenetic trematodes infecting humans are more than 109 species that belong to 49 genera all over the world. According to their habitat in the definitive hosts, they are classified as 6 blood flukes (Schistosoma japonicum. S. mekongi, S. malayensis, S. mansoni, S. intercalatum, and S. haematobium), 15 liver flukes (Fasciola hepatica, F. gigantica, Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Dicrocoelium dendriticum, D. hospes, Metorchis bilis, M. conjunctus, M. orientalis, Amphimerus sp., A. noverca, A. pseudofelineus, Pseudamphistomum truncatum, and P. aethiopicum), nine lung flukes (Paragonimus westermani, P. heterotremus, P. skrjabini, P. skrjabini miyazakii, P. kellicotti, P. mexicanus, P. africanus, P. uterobilateralis, and P. gondwanensis), 30 heterophyid intestinal flukes (Metagonimus yokogawai, M. takahashii, M. miyatai, M. suifunensis, M. katsuradai, M. pusillus, M. minutus, Heterophyes heterophyes, H. nocens, H. dispar, Haplorchis taichui, H. pumilio, H. yokogawai, H. vanissinus, Centrocestus formosanus, C. armatus, C. cuspidatus, C. kurokawai, Procerovum calderoni, P. varium, Pygidiopsis genata, P. summa, Stictodora fuscata, S. lari, Stellantchasmus falcatus, Heterophyopsis continua, Acanthotrema felis, Apophallus donicus, Ascocotyle longa, and Cryptocotyle lingua), 24 echinostome intestinal flukes (Echinostoma revolutum, E. cinetorchis, E. mekongi, E. paraensei, E. ilocanum, E. lindoense, E. macrorchis, E. angustitestis, E. aegyptica, Isthmiophora hortensis, I. melis, Echinochasmus japonicus, E. perfoliatus, E. lilliputanus, E. caninus, E. jiufoensis, E. fujianensis, Artyfechinostomum malayanum, A. sufrartyfex, A. oraoni, Acanthoparyphium tyosenense, Echinoparymphium recurvatum, Himasthla muehlensi, and Hypoderaeum conoideum), 23 miscellaneous intestinal flukes (Brachylaima cribbi, Caprimolgorchis molenkampi, Phaneropsolus bonnei, P. spinicirrus, Cotylurus japonicus, Fasciolopsis buski, Gastrodiscoides hominis, Fischoederius elongatus, Watsonius watsoni, Gymnophalloides seoi, Gynaecotyla squatarolae, Microphallus brevicaeca, Isoparorchis hypselobagri, Nanophyetus salmincola, N. schikobalowi, Neodiplostomum seoulense, Fibricola cratera, Plagiorchis muris, P. vespertilionis, P. harinasutai, P. javensis, P. philippinensis, and Prohemistomum vivax), one throat fluke (Clinostomum complanatum), and one pancreatic fluke (Eurytrema pancreaticum). The mode of transmission to humans includes contact with cercariae contaminated in water (schistosomes) or ingestion of raw or improperly cooked food, including fish (liver flukes, heterophyid flukes, echinostomes, and throat flukes), snails (echinostomes, brachylaimids, and gymnophallid flukes), amphibia, reptiles (neodiplostomes), aquatic vegetables (fasciolids and amphistomes), and insect larvae or adults (lecithodendriids, plagiorchiids, and pancreatic flukes). Praziquantel has been proven to be highly effective against almost all kinds of trematode infections except Fasciola spp. Epidemiological surveys and detection of human infections are required for a better understanding of the prevalence, intensity of infection, and geographical distribution of each trematode species.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts is important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes and hence contribute to reduction of CCA in endemic areas.

High Specificity but Low Sensitivity of Lab-on-a-Disk Technique in Detecting Soil-Transmitted Helminth Eggs among Pre- and School-Aged Children in North-Western Tanzania

An estimated 1.5 billion people are infected with soil-transmitted helminths (hookworms, Ascaris lumbricoides and Trichuris trichiura). These infections are targeted for elimination by the World Health Organization (WHO) by 2030, with the main interventions being mass drug administration using albendazole or mebendazole. Tanzania is one of the endemic countries; it has been implementing MDA to school-aged children for more than a decade and the infection prevalence and intensity of infection have declined. Thus, at this point, the monitoring and evaluation of infection prevalence and intensity of infections, and assessing drug efficacy is crucial and requires accurate diagnostic tests. The currently used standard diagnostic test, the Kato-Katz (KK) technique, has several limitations and the WHO is calling for the development and evaluation of new diagnostic tests. The Lab-on-a-disk (LOD) was developed and tested in the endemic areas of north-western Tanzania to evaluate its sensitivity and specificity using KK and the formol-ether concentration technique. The results showed that when using a duplicate KK slide, the LOD had a sensitivity and specificity of 37.2% (95% CI: 30.7-43.9) and 67.3% (95% CI: 63.1-71.3%). Using four KK slides as a standard technique, the overall sensitivity and specificity were 37.7% (95% CI: 33.1-42.6) and 70.7% (95% CI: 65.5-75.6). The LOD attained high specificity but low sensitivity especially in detecting eggs of Trichuris trichiura. The LOD technique has potential as a promising diagnostic test, but its sensitivity still requires improvement.

Accuracy of a new rapid diagnostic test for urinary antigen detection and assessment of drug treatment in opisthorchiasis

BACKGROUND

Screening for opisthorchiasis, a parasitic worm infection affecting many millions of people in Southeast Asia, has traditionally relied on faecal egg examination such as the formalin-ethyl acetate concentration technique (FECT) and Kato-Katz method. Although the urinary enzyme-linked immunosorbent assay (ELISA) has been used more recently, we developed a urinary antigen-based rapid diagnostic test (RDT) to simplify diagnosis and as a point-of-care testing (POCT) and field applications for surveillance and control of opisthorchiasis.

METHODS

A urinary Opisthorchis viverrini (OV)-RDT was developed using immunochromatographic methodology with a specific monoclonal antibody against OV. The diagnostic performance of the urinary OV-RDT was compared to that of quantitative faecal FECT and urinary antigen ELISA (n = 493). Cross-reactivities of urinary OV-RDT with other helminthiases coexisted with O. viverrini were determined (n = 96). A field trial in the application of urinary OV-RDT was compared with urinary antigen ELISA at baseline screening and assessment of drug treatment outcomes in opisthorchiasis (n = 1629). The McNemar chi-square, Kruskal-Wallis and Cohen's kappa coefficient (κ-value) tests were used for statistical analyses.

RESULTS

Urinary OV-RDT had sensitivity of 94.2% and specificity of 93.2%, compared to faecal FECT. Urinary OV-RDT had high diagnostic agreement (Kappa = 0.842-0.874, P < 0.001) and quantitative correlation with urinary antigen ELISA (Kruskal-Wallis tests = 316.2, P < 0.0001) and faecal FECT (Kruskal-Wallis tests = 362.3, P < 0.0001). The positive rates by OV-RDT, ELISA and FECT were 48.9%, 52.5% and 49.3%, respectively. Cross-reactions of urinary OV-RDT with other helminthiases were few (2%). Field trials of urinary OV-RDT yielded comparable prevalence of O. viverrini between urinary OV-RDT (53.2%) and urinary antigen ELISA (54.0%). OV screening showed high diagnostic agreement (kappa > 0.8, P < 0.0001) between urinary OV-RDT and urinary antigen ELISA. The cure rates of opisthorchiasis at 1 month post-praziquantel treatment determined by urinary OV-RDT (86.6%) and urinary antigen ELISA (80.5%) were similar (P > 0.05).

CONCLUSIONS

The urinary OV-RDT test has high potential as a new tool for screening and evaluating treatment outcomes in opisthorchiasis. The ease of sample collection and simplicity of urinary OV-RDT may facilitate mass screening, control and elimination of opisthorchiasis, thereby contributing to a reduction in the disease burden in Southeast Asia.

Inflammatory cell responses in biliary mucosa during Opisthorchis viverrini infection: Insights into susceptibility differences among hosts

Background

Individual host susceptibility is believed to be a risk factor in the interaction between the host and the parasite. Since studying time series in humans is limited, animal models are replaced.

Aim

This study aims to explore and compare the pattern of inflammatory cell types along the biliary tract and their association with proliferative lesions in the early development of cholangiocarcinoma from susceptible and nonsusceptible animal models.

Methods

Thirty male Syrian golden hamsters and 30 BALB/c mice, serving as the susceptible and nonsusceptible animal models, were used in this comparative study. The animals were infected with 50 Opisthorchis viverrini metacercariae via gastric intubation. At days 1, 2, 7, 14, 28, and 56 postinfection (p.i.), five animals were randomly selected from each group and humanely sacrificed. The hepatobiliary tissues were collected and processed for histopathological study. Histochemical and immunohistochemical staining were applied to differentiate the inflammatory cell types. Kruskal-Wallis and Mann-Whitney tests were applied to assess all semi-quantitative and quantitative variables. The correlation between each variable was also analyzed using Spearman rank at a p-value < 0.05.

Results

The results demonstrated that mice had different patterns of infiltrating cell types when compared to hamsters. This suggested that the cellular response to the infection in mice occurred earlier than that in hamsters. The response in mice reached its peak at D7 to D14 and then rapidly declined at D28. In contrast, although the inflammatory response in hamsters started slowly, the response reached the peak at D28 and maintained a high level until D56. Significant differences in the number of inflammatory cells between mice and hamsters were seen at D1 (p = 0.047), D7 (p = 0.049), D28 (p = 0.040), and D56 (p < 0.040).

Conclusion

The inflammatory responses to O. viverrini infection in the nonsusceptible animal model occurred and declined earlier while the response in the susceptible animal model occurred later in a gradual manner. Both rodents are suitable animal models for the studies of opisthorchiasis susceptibility.

Incidence of fish-borne trematode infections and associated factors: results from a cohort study in highly endemic communities in northern Vietnam

Fish-borne trematodes (FiBT) are an important group of zoonotic parasites negatively affecting human health, mainly in Asia. Most studies on FiBT have applied a cross-sectional design, which provides weaker evidence on potential risk factors for transmission than a cohort study. This cohort study aimed to estimate the incidence and identify associated risk factors for FiBT infection in Vietnam. Between April 2018 and May 2019, two communes in Yen Bai province, a highly endemic area for FiBT, were visited for sampling. Participants with a negative stool result for FiBT at baseline, were invited for follow-up and data collection, at months 4, 9, and 13. Stools were examined using Kato-Katz and formalin-ethyl acetate concentration techniques to detect FiBT eggs, whereas a questionnaire was used for interviewing participants to determine the risk factors for FiBT infection during each follow-up period. The incidence risk and the incidence rate were calculated, and univariate and multivariable models were run to identify the risk factors for FiBT. A total of 194 people, negative for FiBT eggs at the baseline survey, were invited to participate in the study, and 111 people agreed to enroll in the follow-up. The incidence risk at months 4, 9, and 13 was 9.0%, 6.4%, and 5.1%, respectively. We finally used data from 95 participants for the risk factor analysis, excluding 16 people lost for the follow-up. Overall, 20 people became infected with FiBT (IR = 21.1%). The incidence rate of FiBT infection was 21.4/100 person-year. In the univariate analysis, consumption of raw fish was the main risk factor (RR = 4.59, 95%CI = 1.95-10.82), followed by being male (RR = 3.41, 95%CI = 1.56-7.45) and drinking alcohol (RR = 3.25, 95%CI = 1.49-7.11). In the multivariable analysis, only consumption of raw-fish dishes was significantly associated with FiBT infection. The people who consumed raw fish were 3.44 (95%CI = 1.11-10.70) times more at risk of infection with FiBT as compared to individuals who did not consume raw fish. It can be concluded that the FiBT incidence is high in the study area. More awareness campaigns are needed to stop eating raw fish in these areas to reduce FBT infection.

Production and Immunological Characterization of scFv Specific to Epitope of Opisthorchis viverrini Rhophilin-Associated Tail Protein 1-like (OvROPN1L)

(1) Background: Opisthorchis viverrini is a significant health problem in the Mekong subregion of Southeast Asia, causing aggressive cholangiocarcinoma. Current diagnostic procedures do not cover early diagnosis and low infection. Hence, an effective diagnostic tool is still required. Immunodiagnosis seems promising, but attempts to generate monoclonal antibodies have not yet been successful. This study aims to develop a single-chain variable antibody fragment (scFv) against Rhophilin-associated tail protein 1-like (ROPN1L), the sperm-specific antigen of adult O. viverrini, which has not been reported elsewhere. (2) Methods: The target epitope for phage screening was L3-Q13 of OvROPN1L, which showed the highest antigenicity to human opisthorchiasis analyzed in a previous study. This peptide was commercially synthesized and used for phage library screening. The isolated phage was produced in a bacterial expression system and tested for specificity in vitro and in silico. (3) Results: One of fourteen phages, named scFv anti-OvROPN1L-CL19, significantly bound to rOvROPN1L compared with non-infected hamster fecal extracts. This phage clone was successfully produced and purified using Ni-NTA chromatography. Indirect ELISA demonstrated that scFv anti-OvROPN1L-CL19 has a high reactivity with O. viverrini-infected hamster fecal extracts (12 wpi, n = 6) in comparison with non-infected hamster fecal extracts (0 wpi, n = 6), while the polyclonal rOvROPN1L antibodies did not show such a difference. Molecular modeling and docking confirmed our in vitro findings. (4) Conclusion: scFv anti-OvROPN1L-CL19 could be used as an effective material for developing O. viverrini-immunodiagnostic procedures in the future.