Temperature dependence of Opisthorchis felineus infection in the first intermediate host snail, Bithynia troschelii

Opisthorchiasis is one of the most serious trematodiases in Russia, where the world's largest focus is located in the Ob basin. Temperature is an important factor affecting the metabolism of cold-blooded animals. It determines the development of the causative agent of opisthorchiasis, Opisthorchis felineus, and the success of infection of an intermediate host, the snail Bithynia troschelii. In the present study, the effect of water temperature on the development of the liver fluke O. felineus in the host snail was assessed, as was the temperature threshold at which B. troschelii hibernation initiates. Adult uninfected B. troschelii individuals collected from natural bodies of water were infected with O. felineus and maintained at different temperatures of water (18-30 °C, intervals of 3 °C) in the laboratory. Each snail was fed with embryonated uterine eggs of O. felineus at 24 °C. O. felineus infection in snails was detected using polymerase chain reaction (PCR) using specific primers. The prevalence of O. felineus infection in B. troschelii depends on the water temperature in which the snails are maintained. The highest infection rate of 45.2 % ± 12.1 % was observed at 27 °C (p ≥ 0.1). The longest lifespan of infected and uninfected B. troschelii was recorded at water temperatures of 24 and 27 °C. The snails were more successfully infected at the beginning of the warm season. Among the infected individuals, the majority (up to 85 %) were large snails. Cercarial shedding was not detected in experimentally infected snails. Apparently, this is due to the natural physiological state of Bithynia snails during the autumn-winter diapause, when opisthorchiids development in snails stops. At 10 °C, complete hibernation of all B. troschelii snails was observed, and infection by the trematodes became impossible. The highest prevalence of infection was recorded at 27 °C, suggesting that during climate warming, an increase in opisthorchiid infection of snails may occur, which must be considered when epidemiological measures are planned.

Association between Opisthorchis viverrini infection in cats and humans: Non-spatial and spatial analyses

Cats are recognized as significant reservoir hosts for human opisthorchiasis, particularly in areas with a high prevalence of infection. Despite this, the precise role of cats in the transmission of Opisthorchis viverrini between humans and felines remains unclear. This study investigates the association between these two hosts through both spatial and non-spatial analyses in the endemic Thanya sub-district of Thailand. A total of 105 owned cats were randomly sampled from 15 villages within the sub-district for stool examination. A questionnaire was administered to 66 cat owners to explore the human-pet relationship. Household locations were collected using GPS devices. Non-spatial analyses revealed a positive association between the two hosts (P= 0.011; OR 7, 95% CI: 1.6-30.9), highlighting two independent significant risk factors: cat owners consuming raw fish (P = 0.028; OR = 4.52, 95% CI: 1.25-19.45) and feeding cats raw fish (P = 0.011; OR = 16.41, 95% CI: 2.78-317.04) according to multivariate analysis. Spatial analysis provided further support to the non-spatial findings (p = 0.0123; OR = 3.45, 95% CI = 0.88-13.61). Multiple autologistic regression confirmed two significant risk factors: cat owners consuming raw fish (p = 0.054; OR = 3.37, 95% CI: 0.98-11.59) and feeding cats raw fish (p = 0.014; OR = 7.43, 95% CI: 1.49-37.05). Risk mapping identified the western part of the study site as a hotspot for O. viverrini infection. Hyper-endemic focusing revealed a union of human and cat buffers at 0.46 km², with an overlapping area of 0.22 km² (47.83%). This study underscores the impact of owners' behaviors, specifically consuming and feeding raw fish to cats, on the increased probability of infection in cats. It emphasizes the need for effective opisthorchiasis control through health education targeting cat owners in endemic areas.

Inflammatory responses to Opisthorchis viverrini infection in animal models: A comparison between susceptible and nonsusceptible hosts in different anatomical locations

Background

Inflammation caused by Opisthorchis viverrini infection increases the risk of cholangitis, cholecystitis, and leads to bile duct cancer (cholangiocarcinoma or CCA). However, only certain infected individuals are susceptible to CCA, suggesting the involvement of host factors in cancer development. In addition, there are reports indicating differences in the locations of CCA.

Aim

This study aims to investigate cellular inflammatory responses in the common bile duct (CB), intrahepatic bile duct (IHB), and gallbladder (GB) in susceptible and non-susceptible hosts following O. viverrini infection.

Methods

Thirty Syrian golden hamsters (a susceptible host) and 30 BALB/c mice (a non-susceptible host) infected with O. viverrini were studied at six time points (five animals per group). Histopathological evaluations were conducted on samples from the IHB, CB, and GB. Inflammatory cell infiltration was quantitatively assessed and compared between groups and time points. Statistical analysis was performed using one-way ANOVA, with a significance level of p < 0.05.

Results

Inflammation was significantly more pronounced in the IHB compared to the other two biliary locations. In comparison between susceptible and non-susceptible hosts, the intensity of inflammation was higher in the OV+H group than in the OV+M group (p < 0.05).

Conclusion

This study highlights the association between host response to inflammation, tissue location, and host susceptibility, with the IHB showing particular susceptibility to inflammation and pathological changes. These findings contribute to our understanding of the increased risk of CCA in susceptible hosts.

Microsatellite markers for Opisthorchis felineus to understand its genetic diversity and transmission patterns of opisthorchiosis

Opisthorchis felineus is a food-borne trematode which causes opisthorchiosis and affects mainly the liver and bile ducts of the liver with a possible risk of bile duct carcinogenesis resulting in cholangiocarcinoma. In Russia, O. felineus is mainly endemic in Western Siberia (Ob and Irtysh river basins) and occurs throughout the Volga, Kama, Don, and Dnepr river basins. The prevalence, intensity, and clinical significance of human infections and the incidence of cholangiocarcinoma vary geographically in endemic regions. Currently, there is substantial evidence on genetic variation of O. felineus, but information on the population genetic structure is so far very scarce. Because microsatellite DNA of this parasite is not available, we for the first time isolated sufficient microsatellite loci to examine the genetic diversity and population structure of O. felineus, using multiple nuclear loci approach. A total of ten highly polymorphic microsatellite loci from a constructed enriched genomic DNA library were characterized, using 29 samples representing huge O. felineus metapopulation extended in latitude over 5000 km from Middle Europe to Western Siberia. At least three populations can be discerned as result of analysis of the microsatellite loci genetic diversity. Based on the results for the first time, a hypothesis was put forward about the formation of a modern habitat of O. felineus.

Roaming behavior of the owned domestic cats (Felis catus) with possible roles in the transmission of Opisthorchis viverrini in the endemic area in Khon Kaen, Thailand

In the endemic area of the liver fluke (Opisthorchis viverrini) infection, effective control of opisthorchiasis using One Health approaches requires transmission interruption in all hosts in the parasite life cycle. Owned domestic cats (Felis catus) are considered an important species among mammalian reservoirs. Similar to humans, household cats become infected by eating raw, contaminated fish and spread the O. viverrini eggs to the environment by defecation. In rural areas, cat owners usually feed their cats with human food or food waste, especially fish dishes. There is a high risk for cats to become infected and deposit eggs in the peri-household environment. The lack of research on domestic cats led us to study their roaming behavior, roaming range, habitat preference and risk of disease transmission. GPS loggers were harnessed to 28 domestic cats in 7 villages around Lawa Lake, the endemic area of human opisthorchiasis. All cats were examined for the O. viverrini infection status using modified formalin-ether concentration technique (MFECT) before application of the GPS device used to observe and record their roaming distance and range area. Then, composition analysis for habitat selection was performed using the location data. Additionally, cat owners were interviewed using participatory epidemiologic methods for their perceptions and knowledge about the reservoir hosts of this trematode. Our study suggested that the prevalence of O. viverrini in cats in this area has not declined appreciably in comparison with our previous study four years ago, although the treatment and control has been applied intensively in humans. The longest distance that individual cats roamed ranged from 51 to 363 meters (mean±SD = 154.48±90.71). The cats traveled tracks around their home. There was no significant difference in the average distance that cats ranged between O. viverrini infected group (154.13±72.80 meters) and the non-infected group (154.67±101.39 meters) was found. Compositional analysis suggested that the domestic cats preferred urban habitats where food and safety were probably more available. It appears that the main transmission route for infection of cats was contaminated fish fed to cats or fish that remained in their houses. Therefore, owners should refrain from feeding their cats potentially contaminated foods, food scraps and raw fish remains and prevent their cats from accessing them. Moreover, the participatory epidemiology results suggest that awareness of villagers is not enough for the effective and sustainable control of the disease.

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.

Similarities and differences among the Opisthorchiidae liver flukes: insights from Opisthorchis felineus

The foodborne liver trematode Opisthorchis felineus (Rivolta, 1884) is a member of the triad of phylogenetically related epidemiologically important Opisthorchiidae trematodes, which also includes O. viverrini (Poirier, 1886) and Clonorchis sinensis (Loos, 1907). Despite similarity in the life cycle, Opisthorchiidae liver flukes also have marked differences. Two species (O. viverrini and C. sinensis) are recognized as Group 1A biological carcinogens, whereas O. felineus belongs to Group 3A. In this review, we focus on these questions: Are there actual differences in carcinogenicity among these 3 liver fluke species? Is there an explanation for these differences? We provide a recent update of our knowledge on the liver fluke O. felineus and highlight its differences from O. viverrini and C. sinensis. In particular, we concentrate on differences in the climate of endemic areas, characteristics of the life cycle, the range of intermediate hosts, genomic and transcriptomic features of the pathogens, and clinical symptoms and morbidity of the infections in humans. The discussion of these questions can stimulate new developments in comparative studies on the pathogenicity of liver flukes and should help to identify species-specific features of opisthorchiasis and clonorchiasis pathogenesis.

Does Opisthorchis viverrini circulate between humans and domestic cats in an endemic area in Thailand?

The liver fluke Opisthorchis viverrini is a foodborne trematode that, in chronic infection, is a leading cause of bile-duct cancer – cholangiocarcinoma. Cats and dogs are acknowledged as reservoir hosts of this parasite. However, this assumption is based on morphological similarity of flukes recovered from these hosts, without any molecular genetic evidence. The aim of this study was to obtain molecular data from O. viverrini eggs present in feces of humans and cats in the same locality in Thanya sub-district, Kalasin, Thailand. The mitochondrial cytochrome c oxidase subunit 1 (cox1) gene was used as the marker for a population-genetic study. A DNA fragment of the cox1 gene was amplified from stool samples and subjected to nucleotide sequencing. Phylogenetic and haplotype network analyses were performed. The cox1 sequences of O. viverrini eggs from humans and cats largely formed separate clades on the phylogenetic trees, with an Fst value of 0.64 (P < 0.05), indicating largely distinct populations in the 2 species. However, 5 samples from cats were placed in the human cluster and 1 sample from a human was placed in the cat cluster. This suggests that host specificity of ‘human’ and ‘cat’ clades is not absolute. These results indicate that there are 2 populations of O. viverrini, one circulates primarily in humans and the other in cats. However, cross-transmission can occur between these 2 hosts. Taken altogether, the population-genetic evidence from this study partially supports the assumption that the cat can act as a reservoir host of O. viverrini.

A MULTIPLEX PCR ASSAY FOR THE DIFFERENTIAL DETECTION OF OPISTHORCHIS FELINEUS AND METORCHIS BILIS

Opisthorchis felineus and Metorchis bilis are two common small worms that parasitize in the gallbladder and bile ducts of the liver of humans and carnivores. These parasites have a severe impact on health and are considered pathogens of serious diseases worldwide, such as cholangiocarcinoma. However, there are still no commercially available molecular diagnostic kits capable of simultaneously detecting these parasites in humans. Therefore, the study aimed to develop a multiplex PCR analysis that will differentially determine these two opisthorchiasis infections in one reaction. Two specific primer pairs for a multiplex polymerase chain reaction (PCR) were designed based on corresponding mitochondrial genome sequences. The multiplex assay detection limit was assessed by serial dilutions of the genomic DNAs of trematode worms examined. Naturally, infected samples of human bile and feces were tested using the developed assay. A multiplex PCR assay was developed based on mitochondrial DNA that accurately and simultaneously identifies two trematode species in one reaction using specific fragment sizes of 307 and 252 bp for O. felineus and M. bilis, respectively. The optimal reaction conditions, specificity, and sensitivity of the multiplex PCR assay were investigated. The lowest DNA concentration detected was 100 pg for M. bilis and O. felineus in a 25μl reaction system. This study provides an efficient tool for the simultaneous detection of O. felineus and M. bilis. The proposed multiplex PCR assay will be potentially useful in epidemiological studies, diagnosis, and treatment of this mixed opisthorchiasis infection.

Low-Grade Endemicity of Opisthorchiasis, Yangon, Myanmar

We performed an epidemiologic survey of opisthorchiasis in Yangon, Myanmar. The fecal egg-positive rate of residents was 0.7%, and we recovered an adult fluke after chemotherapy and purging of an egg-positive resident. We detected Opisthorchis viverrini metacercariae in freshwater fish. We found the Yangon area to have low-grade endemicity of opisthorchiasis.

Effects of aestivation on survival of Bithynia siamensis goniomphalos snails and the infection of Opisthorchis viverrini in the irrigation area of wet- and dry-season rice paddy

The snail Bithynia siamensis goniomphalos acts as the first intermediate host of the human liver fluke, Opisthorchis viverrini, a major cause of cholangiocarcinoma in Northeast Thailand. In this study, we investigated host-parasite interactions in wet- and dry-season rice paddy plantation. The snails that aestivated through 4-month-dried period after rice harvest had average mortality rate of 36.45% and monthly increasing from 17.76% to 54.57%. Surprisingly, at depths greater than 5 cm experienced a higher mortality rate than upper level. Average mortality rate at the depth more than 5 cm, was 42.97%. In the initial month of aestivation, mortality rate of 0-5 and 5-10 cm depth was 9.13% and 26.39% then increase to 57.58% and 51.97%, respectively in the last 4th month. The average prevalence O. viverrini infection in snails during the study period was 0.44%. The highest prevalence of O. viverrini infection was found in the cool dry and wet season. The odds of O. viverrini infection in female snails and large snails were higher relative to male snails and medium-sized snails. The physicochemical factors involved in increased prevalence of O. viverrini infection in snail hosts were mean daily air temperature and average monthly rainfall. Short aestivation period made lower mortality in irrigation area than the previous report of non-irrigation area, that is, the aestivation is one of snail population control.

Biliary cystadenoma associated with Opisthorchis viverrini infection in a domestic cat (Felis catus)

A 12-year-old, female, domestic cat (Felis catus) presented with dehydration, emaciation, anorexia, and lethargy. The cat was unresponsive to medical treatment and euthanized; the carcass was submitted for pathological diagnosis. Necropsy revealed icteric mucous membranes. The liver was enlarged, with multinodular, cystic, white masses, 0.5-4.0 cm in diameter, scattered throughout. Microscopically, the biliary epithelium presented with a proliferation of multifocal cystic masses, occasionally with periodic acid-Schiff-positive fluid within the cysts. Simple cuboidal epithelial cells showed small, round to oval, vesicular nuclei and rare mitotic figures. There were also multifocal trematode-like parasites situated within the biliary tracts. Immunohistochemistry of the cystic masses was positive for pan-cytokeratin and proliferating cell nuclear antigen, while negative for vimentin. Molecular analysis and gene sequencing of the parasite indicated that it was Opisthorchis viverrini. Based on the pathological findings and molecular analysis, the cat was diagnosed with biliary cystadenoma related to O. viverrini infection. This report described an unusual case of O. viverrini infection associated with biliary tumor in a cat, and raises the possibility of domestic cats as a reservoir host of the human liver fluke.

Updated molecular phylogenetic data for Opisthorchis spp. (Trematoda: Opisthorchioidea) from ducks in Vietnam

BACKGROUND

An opisthorchiid liver fluke was recently reported from ducks (Anas platyrhynchos) in Binh Dinh Province of Central Vietnam, and referred to as "Opisthorchis viverrini-like". This species uses common cyprinoid fishes as second intermediate hosts as does Opisthorchis viverrini, with which it is sympatric in this province. In this study, we refer to the liver fluke from ducks as "Opisthorchis sp. BD2013", and provide new sequence data from the mitochondrial (mt) genome and the nuclear ribosomal transcription unit. A phylogenetic analysis was conducted to clarify the basal taxonomic position of this species from ducks within the genus Opisthorchis (Digenea: Opisthorchiidae).

METHODS

Adults and eggs of liver flukes were collected from ducks, metacercariae from fishes (Puntius brevis, Rasbora aurotaenia, Esomus metallicus) and cercariae from snails (Bithynia funiculata) in different localities in Binh Dinh Province. From four developmental life stage samples (adults, eggs, metacercariae and cercariae), the complete cytochrome b (cob), nicotinamide dehydrogenase subunit 1 (nad1) and cytochrome c oxidase subunit 1 (cox1) genes, and near-complete 18S and partial 28S ribosomal DNA (rDNA) sequences were obtained by PCR-coupled sequencing. The alignments of nucleotide sequences of concatenated cob + nad1 + cox1, and of concatenated 18S + 28S were separately subjected to phylogenetic analyses. Homologous sequences from other trematode species were included in each alignment.

RESULTS

Phylogenetic trees were inferred from concatenated (cob + nad1 + cox1) nucleotide sequences and combined 18S + 28S nucleotide sequences of five Opisthorchis sp. BD2013 samples and additional reference taxa. Both trees demonstrated the anticipated clustering of taxa within the superfamily Opisthorchioidea, the paraphyly of the genus Opisthorchis and the sister-species relationship of Opisthorchis sp. BD2013 with O. viverrini.

CONCLUSIONS

While it is likely that Opisthorchis sp. BD2013 is distinct from O. viverrini, it is clearly a sister taxon of O. viverrini within the limited number of Opisthorchis species for which appropriate sequence data are available. The new sequences provided here will assist the diagnosis and the taxonomic clarification of the opisthorchiid species.

PREVLENCE AND RISK FACTORS FOR OPISTHORCHIS VIVERRINI INFECTION AMONG CATS AND DOGS IN SIX DISTRICTS SURROUNDING THE UBOLRATANA DAM, AN ENDEMIC AREA FOR HUMAN OPISTHORCHIASIS IN NORTHEASTERN THAILAND

Opisthorchis viverrini is a zoonotic liver fluke that causes opisthorchiasis among humans in endemic areas, such as northeastern Thailand. The objective of this study was to determine the prevalence and risk factors for O. viverrini infection among cats and dogs in six districts surrounding Ubolratana Dam. Fecal samples of 1,018 dogs and 249 cats were collected between 2008 and 2013 to examine for O. viverrini infection using a modified formalin-ether concentration technique. The prevalence of O. viverrini infection among cats (77 of 249, 30.92%) was higher than dogs (2 of 1,018, 0.20%). Age and the eating habits of cats were associated with O. viverrini infection. Cats aged >3 years were more likely than those aged <1 year [Odds ratio (OR)=2.96; 95% confidence interval (95% CI): 1.01- 8.35; p = 0.044] of being infected. Cats that consumed raw fish were significantly more likely to be infected than those that consumed other foods (OR=1.82, 95% CI: 1.05-3.16; p = 0.032). Cats had a higher prevalence of O. viverrini infection than dogs and may play an important role in the transmission and maintenance of this disease in the study area.

Andrographolide Ameliorates Beta-Naphthoflavone-Induced CYP1A Enzyme Activity and Lipid Peroxidation in Hamsters with Acute Opisthorchiasis

BACKGROUND

Opisthorchis viverrini (OV) infection generates oxidative stress/free radicals and is considered as a primary cause ofcholangiocarcinoma since it primarily triggers sclerosing cholangitis.

OBJECTIVE

In this study, the impacts of andrographolide on acute opisthorchaisis in β-naphthoflavone (BNF)-exposed hamsters were investigated.

MATERIAL AND METHOD

Ethoxyresorufin O-deethylase (EROD) and methoxyresorufin O-demethylase (MROD) activities and Thiobarbituric acid reaction substances (TBARS) assay of andrographolide in acute opisthorchiasis in the BNF-exposed hamsters were assessed.

RESULTS

The results showed that andrographolide ameliorated the hepatic CYP1A1 and CYP1A2 activities by decreases of the specific enzymatic reactions of EROD and MROD, respectively, in the BNF-exposed hamsters. Moreover, andrographolide lowered the formation of malondialdehyde in the livers and brains of the hamsters.

CONCLUSION

These observations revealed the promising chemo-protective and antioxidant activities of andrographolide via suppression of the specific EROD and MROD reactions and lipid peroxidation against acute opisthorchiasis in the BNF-exposed hamsters.

TREMATODE INFECTION OF FRESHWATER SNAIL, FAMILY BITHYNIIDAE IN THAILAND

Opisthorchis viverrini is restricted to and requires for its aquatic life cycle only Bithynia snail as first intermediate host but many species of cyprinid fish as second intermediate hosts. A survey in Thailand of trematode infection in freshwater snails of the family Bithyniidae carried out during October 2008 - July 2009 found a total of 5,492 snails, classified into ten species distributed in various geographic areas. Bithyniafuniculata and Gabbia pygmaea were localized to the north, B. s. goniomphalos, Wattebledia siamensis and W. crosseana to northeast and B. s. siamensis, Hydrobioides nassa and G. wykoffi to central region. W. baschi and G. erawanensis was found only in the south and Erawan waterfall, Kanchanaburi Province, respectively. Trematode infection rate was 3.15%. Cercariae were identified as belonging to six types, namely, amartae , monostome, mutabile, O. viverrini, virgulate, and unknown. The prevalence of cercarial infection in B. s. goniomphalos of amartae, mutabile, O. viverrini, virgulate, and unknown type cercaria was 0.55%, 0.74%, 1.07%, 2.87%, and 0.37%, respectively, and in B. s. siamensis monostome (1.10%) and virgulate (0.55%). Only virgulate cercariae were shed from W. crosseana (3.85%) and W. siamensis (5.19%). Cercariae of the unknown type were found in G. wykoffi (1.69%). No infection of O. viverrini cercariae was detected in the other species.

Experimental infection of Opisthorchis viverrini cercariae to the cyprinid fish, Barbonymus gonionotus

Opisthorchis viverrini is an important public health problem, a major cause of cholangiocarcinoma in the Greater Mekong subregion including Lao PDR, Cambodia, Vietnam and Thailand. Humans acquire the infection by consumption of raw, fermented or partially cooked freshwater cyprinid fish containing infective metacercariae. This study examined the effect of cercarial infection dosage (25-200 cercariae), age (1-60 day) and size (1-24mm) of Barbonymus gonionotus fish on infection success of O. viverrini cercariae. Additionally, the site of cyst formation of O. viverrini cercariae and subsequent development to the metacercariae was examined. The result showed that cercarial infection dose (F4,95=8.52, P<0.001) age (P<0.001, ƛLR(2)=954.72) and size (P<0.001, ƛLR(2)=1204.84) were significantly associated with number of O. viverrini metacercariae recovery with in every additional fish age, the O. viverrini metacercarial recovery rate increased by 5.4% (P<0.001). Most metacercariae were found in the body of the fish (81.4%). We concluded that O. viverrini cercarial infection dosage, and age and size of fish were important determinants for a successful infection to fish.

[Infection with opistorchis larvae in the fish family cyprinidae in the Ob-Irtysh River basin in the Tyumen region]

Fishes, such as ide (Leuciscus idus), dace (Leuciscus leuciscus), carpbream (Abramis brama), roach (Rutilus rutilus), and muvarica (Alburnus alburnus), with different frequency and rate of invasion and abundance index were infested with larvae of O. felineus, M. bilis, and P. truncatum. There were the highest rates of fish infection with P. truncatum larvae in the subtaiga zone (the south of the region) and with O. felineus metacercariae in the northern subtaiga and taiga zones. In research, experimental, and clinical studies, the nosological entity opisthorchiasis is a parasitic cenosis consisting of 2-3 co-members requiring their specific identification, which allows therapeutic measures to be more effectively implemented among the population of a hyperendemic focus.

[Continuous blood coagulation in chronic opisthorchiasis]

Animal experiments have shown that chronic Opisthorchis invasion results in accelerated continuous blood coagulation, by inducing hypercoagulation and platelet activation. The state of hemostasis depends on the degree of infection and undergoes the largest changes during maximum invasion. Irrespective of invasion rates, chronic opisthorchiasis is accompanied by hypofibrinogenemia.

[Complicated forms of superinvasion opisthorchiasis: pathogenetic aspects]

Superinvasion opisthorchiasis is characterized by host growth retardation and weight reduction, which are due to the cleptoeffect of Opisthorchis felineus; metabolic disturbances, proliferative processes, accelerated collagen biosynthesis and biodegradation in the organs reflect parasite-host interactions as components of the system. The productive reactions of visceral pathology are initiated by the parasite's metabolites located in the liver, lung, heart, and testes.

Prevalence of Opisthorchis viverrini infection in the canine and feline hosts in three villages, Khon Kaen Province, northeastern Thailand

To determine the current reservoir status and prevalence of Opisthorchis viverrini infection in endemic areas, 78 dogs and 22 cats were sampled for fecal examination in 3 villages along the Chi River in Khon Kaen Province, northeastern Thailand. Sex, age, color, identifiable markings, subjective body condition scores (BCS) and diet were recorded and analyzed. Fecal samples were evaluated using direct smear and modified formalin-ethyl acetate fecal assays. All parasites found were identified. In dogs and cats, the prevalences of O. viverrini infection were 3.8% and 36.4%, respectively. The highest prevalences of parasitic infection in both dogs and cats were Ancylostoma spp, in 64.1% and 77.3%, respectively. These results provide insight into the role of the canines and felines in maintaining the presence of O. viverrini eggs in the environment. If similar patterns occur on a broader scale, the zoonotic role of dogs and cats in the epidemiology of this disease should be considered in the development of improved control and education programs.

A novel nuclear marker, Pm-int9, for phylogenetic studies of Opisthorchis felineus, Opisthorchis viverrini, and Clonorchis sinensis (Opisthorchiidae, Trematoda)

Opisthorchis felineus, O. viverrini, and Clonorchis sinensis, the trematodes of the family Opisthorchiidae, are important human parasites. Two previous studies (Kang et al. Parasitol Int 57:191-197, 2008; Katokhin et al. Dokl Biochem Biophys 421:214-217, 2008) have provided evidence using ribosomal and mitochondrial sequences that O. viverrini, O. felineus, and C. sinensis are closely related. We developed a novel nuclear marker, Pm-int9, which included the ninth intron of the paramyosin gene and flanking exon sequences. Samples of O. felineus from four localities of West Siberia, C. sinensis from the Russian Far East, and O. viverrini from Thailand were genotyped by Pm-int9. Little variation was detected in exon sequences, however, intron sequences turned out to be more variable than ribosomal internal transcribed spacers. We can conclude that Pm-int9 is valuable for interspecific variation studies. Phylogenetic analysis based on Pm-int9 revealed that O. viverrini and C. sinensis were closer to each other than either of them to O. felineus, supporting the opinion that C. sinensis should be considered the sister species of Opisthorchis spp.

Genetic variation at three enzyme loci within a Thailand population of Opisthorchis viverrini

Genetic variation among 231 individuals of Opisthorchis viverrini from the Ban Phai District, Khon Kaen Province (Thailand) was examined at three polymorphic enzymes: enolase (ENOL), phosphoglucomutase (PGM), and triose phosphate isomerase (TPI). Four alleles were detected for TPI and PGM, whereas only two alleles were detected for ENOL. The inferred genotype frequencies for both TPI and ENOL were not significantly different from Hardy-Weinberg equilibrium. In contrast, the inferred genotype frequencies for PGM showed a significant departure from Hardy-Weinberg equilibrium, with a lack of heterozygous individuals. This heterozygote deficiency suggests non-random mating and/or potentially high self fertilization.

[Metazoan parasites of fishes from the Bug River]

Results if the ichthyoparasitological investigation of the Bug River carried out in 1996-1999 are reported. Twenty-nine metazoan parasite species from 7 classes were found in fishes from the studied area, with the total infestation rate 63.9%. Thirteen of them parasitize fish at larval stages. Metacercariae of Opisthorchis felineus, which ate the agents of opisthorchosis in man and animals, were found in roach.

[Ecological bases of the combination of natural foci of Trematoda infections in the floodplain-river ecosystem of the Konda River. Communication 2. Host population-combined foci of Trematoda infections]

In the context of the present-day teaching of parasitocenoses and the proposition that the pathogen's population is the only compulsory and specific component of a natural focus, the author discloses the ecological bases of the combination of natural foci of opisthorchiasis and methorchiasis (M. bilis), methorchiasis (M. bilis) and methorchiasis (M. xanthosomus). These foci are host population-combined. While analyzing the combination of foci, it is expedient to consider them in pairs since this provides a way of identifying only the combination bases that are unique to these foci. The parasitic systems of flukes, the parasitocenoses of co-acting parasitic systems of "twin types", the structure of foci, the species-specific composition of ecosystems, and the ecological relations of the Opisthorchis fluke hosts act as the biotic bases of a combination of foci of Trematoda infections. By coinciding, the multihost hemipopulations of parasites and the susceptibility of host populations predetermine the combination of Opisthorchis fluke foci. The susceptibility of hosts, the multihost pattern of Opisthorchis flukes, the identity of parasitic systems, and the common mechanism of pathogen transmission act as the epizootic bases of a combination of invasion foci. The morphological structure and hydrological regime of a landscape act as the abiotic bases of a combination of foci. The hydrological regime is by its nature a universal mechanism of pathogen transmission. The foci of Opisthorchis flukes at the level of parasitocenosis of metacercarium populations and fish populations in the Konda River ecosystem are combined in the age groups of only carp (Cyprinidae) underyearlings and yearlings. The abiotic, biotic, and epizootic bases of a combination of natural foci of Opisthorchis flukes are, in the aggregate, the ecological bases of a combination of foci.

Evidence of a species complex within the food-borne trematode Opisthorchis viverrini and possible co-evolution with their first intermediate hosts

The food-borne trematodes, Opisthorchis viverrini, O. felineus and Clonorchis sinensis, have long been recognized as the cause of major human health problems, with an estimated 40 million infected persons. Of the three species of liver fluke, only O. viverrini is classified as a type 1 carcinogen because of its role as an initiator of chronic inflammation and the subsequent development of cholangiocarcinoma. At present, there are no techniques for the early diagnosis of cholangiocarcinoma and it is fatal for most patients. There is considerable variation in parasite prevalence and disease presentation in different geographical areas, the latter of which may be associated with genetic differences among parasites. In the present study, multilocus enzyme electrophoresis was used to provide a comprehensive genetic characterization of O. viverrini from different geographical localities in Thailand and the Peoples’ Democratic Republic of Laos. Parasites from different localities were compared genetically at 32 enzyme loci. The results of the genetic analyses are sufficient to reject the null hypothesis that O. viverrini represents a single species. Therefore, O. viverrini consists of at least two genetically distinct, yet morphologically similar (i.e. cryptic) species. Moreover, there was also separation of the different populations of snails (i.e. the first intermediate hosts) into two distinct genetic groups that corresponded with the delineation of O. viverrini into two species. This suggests that there may be a history of co-evolution in this host–parasite lineage. Additionally, five distinct genetic groups of parasites were detected, each of which occurred within a different and independent river wetland system. Our findings have major implications for the implementation of effective control and surveillance programs targeted to these medically important food-borne parasites.

Genetic markers for the identification and characterization of Opisthorchis viverrini, a medically important food borne trematode in Southeast Asia

The liver fluke, Opisthorchis viverrini, is one of the major food borne trematodes in Southeast Asia, where infection causes hepatobiliary disease and subsequent development of cholangiocarcinoma. In Thailand, O. viverrini is most prevalent in the northeast where there is marked regional variation in the rate of infection in humans at provincial, district and village levels. To date, the roles of genetic variation of O. viverrini on this observed variability in infection, transmission and associated disease are not known. We have applied multilocus enzyme electrophoresis (MEE), specifically allozyme electrophoresis, to isolates of O. viverrini from Thailand and Laos to establish genetic markers to examine its systematics and population structure. Forty-six enzymes commonly found useful for genetic characterisation in parasitic helminths were screened, and of these, 33 enzymes gave sufficient staining and resolution to act as potential genetic markers. Sixteen enzymes were monomorphic and 17 enzymes were polymorphic in the pools of worms examined. Whether they are indicative of different enzyme loci, heterozygosity or unique genotypes within the pools of worms examined remains to be determined. Preliminary investigations examining five individual worms at enzyme loci where pools of worms showed multiple bands have confirmed the diagnostic value of the enzyme loci established as well as providing evidence of potential population sub structuring and heterozygosity. For the first time, we have established at least 17 enzymes that provide the basis to undertake comprehensive genetic analyses of the systematics and population structure of O. viverrini, a medically important food borne trematode in Southeast Asia.

Enzyme markers to identify and characterize Opisthorchis viverrini in Thailand and Lao PDR

We conducted an allozyme electrophoretic study to explore potential enzyme markers to distinguish Opisthorchis viverrini in Thailand and Lao PDR. Twenty-eight enzymes encoding presumptive 32 loci were established. The enzymes glucose-6-phosphate dehydrogenase and pyruvate kinase were diagnostic between two geographically separate isolates from Thailand. Twelve enzymes, ie, aconitate hydratase, aldolase, creatine kinase, enolase, esterases, fumarate hydratase, aspartate aminotransferase, glucose-phosphate isomerase, alanine aminotransferase, isocitrate dehydrogenase, malic enzyme, and pyruvate kinase, also provided diagnostic markers for these two isolates from Thailand and one isolate from Lao PDR.

[Influence of environmental factors on the infection rates of fishes and shellfishes by trematodes of the Opisthorchidae family in the Krotovaya Lyaga Lake]

The relationship of the annual trends in the infection of crucians (Carassius carassius) (L.) with Opisthorchis felineus metacercariae, in that of verkhovkas (Leucasplius delineatus) (Hackel), and in that of lake minnows (Phoxinus percnurus) (L.) with O. felineus and Metorchis billis to the environmental factors under natural fluctuations of the level of water and under the man-made effects on the water regime of the reservoir was studied. When the level of water naturally changes, the infection of crucians with Metorchis was found to be affected by their size, water temperature, and environmental pH values, and the human Opisthorchis affliction depends on the severity of infection of commercial-sized crucians by metacercariae. The infestation of the verkhovka was determined by the temperature of water and that of the lake minnow was by its size and the increased areas of the lake with the depths salubrious to its existence. With man-made effects (dewatering for watering agricultural lands) on the water regime of the reservoir, the infestation of the lake minnow depended on its size in the shallow water and on the level of water. Environmental factors, such as pH values, the area of shallow waters, and the size of mollusks, positively affected the higher extensiveness of infestation of mollusks with the parthenitae of opisthorchid flukes.

Molecular characterization and differentiation of opisthorchiid trematodes of the species Opisthorchis felineus (Rivolta, 1884) and Metorchis bilis (Braun, 1790) using polymerase chain reaction

Adult specimens of the opisthorchiid liver fluke species Opisthorchis felineus and Metorchis bilis could be identified for the first time by molecular biological methods using species specific primers (OF and MB primers) in the polymerase chain reaction (PCR). The OF or MB primers were based on a part of the mitochondrial cytochrome c oxidase I gene. A specific product of approximately 200 bp could be amplified for O. felineus by means of the specific O. felineus primers. By contrast, the amplification of M. bilis DNA with MB primers produced a fragment of approximately 110 bp. A specificity of 100% could be demonstrated for both primer pairs. The sensitivities of the PCRs were 10 pg for the O. felineus DNA and 100 fg for the M. bilis DNA.

A sero-epidemiological survey on the occurrence of opisthorchiid liver flukes in red foxes ( Vulpes vulpes) in Berlin, Germany

Serum samples collected from red foxes in the city of Berlin between 1996 and 1999 were analysed for the presence of antibodies against Opisthorchis felineus and Metorchis bilis using an indirect ELISA. Out of 1,000 specimens, 30.6% and 46.5% reacted positively with specific O. felineus and M. bilis antigens, respectively. Seroprevalence in adult foxes was always higher than in juveniles. While no significant differences were observed in adult foxes throughout the period, in juvenile specimens seroprevalence declined from 1996 to 1997, then stayed at a comparable level in 1998 and increased in 1999. A varying availability of fresh cyprinid fish in different years seems to be the reason for changes in seroprevalence. By grouping the samples from juvenile foxes by season, antibodies against both Metorchis and Opisthorchis antigens started to appear between April and June, increased between July and September()and reached a level comparable to adult foxes in the October to December quarter. The lowest seroprevalence was found in Pankow, which is the district with the lowest share of the surface water.

Liver enzyme activity and histological changes in the liver of silver foxes (Vulpes vulpes fulva) experimentally infected with opisthorchiid liver flukes. A contribution to the pathogenesis of opisthorchiidosis

Blood samples from silver foxes experimentally infected with Opisthorchis felineus and Metorchis bilis, respectively, were examined for the activity of liver enzymes. The average activities of aspartate aminotransferase (AST), glutamate dehydrogenase (GLDH), alkaline phosphatase and alanine aminotransferase in uninfected control animals were 20, 1.8, 57 and 44 units/l, respectively. The liver enzymes in infected foxes reacted differently, depending on dose, species of flukes and individual peculiarities. The highest individual deviation of infected from control animals was registered in the case of GLDH, reaching increases of up to 200-fold. In contrast, AST showed the lowest deviation from control values (less than 10-fold). By the end of the study period, enzyme activities had declined. The prepatent periods for M. bilis and O. felineus in foxes were 2 weeks and 4 weeks, respectively. High egg per gram values were established at the beginning of the patent period. At necropsy, chronic inflammatory reactions were found in the bile ducts and in the wall of the gall bladder. The number of flukes at the end of the study was low.

[Fish infection with Opisthorchis larvae in Russia and some contiguous countries (by the materials of the "Cadaster of opisthorchis infection foci in Russia in 1994"]

A cadastre of opisthorchiasis foci with places under study and specious fish invasion with larvae of this helminthiasis has been first drawn up. Opisthorchis larvae have been found to be recorded in 23 species and 2 subspecies of the Cyprinidae family and 1 species of the Cobitidae family. The cadastre permits the areas epidemiologically hazardous due to opisthorchiasis to be determined. The data on fish species-specific infection in different river basins may render a great deal of aid to sanitary-and-epidemiological surveillance workers in implementing preventive measures in specific regions.

Development of a PCR-based method for the detection of Opisthorchis viverrini in experimentally infected hamsters

Opisthorchis viverrini infection is an endemic disease that causes a serious public health problem in southeast Asia, especially in northeast Thailand. We have developed a PCR method using a pair of primers named OV-6F/OV-6R for detecting O. viverrini eggs in stool samples and compared it with Stoll's egg-count method. The primers were designed based on the pOV-A6 specific DNA probe sequence which gave a 330 base pair product. The PCR method can detect a single egg in artificially inoculated faeces or as little as 2 x 10(-17) ng of O. viverrini genomic DNA. The method gave 100% sensitivity in all hamster groups except in animals exposed to the lowest intensity of infection (1 metacercaria/hamster). In the first month of infection, the PCR method was more sensitive than using the egg-count method in all infected groups especially in the light infections. The PCR method was also successfully used in monitoring a therapeutic study. Since the PCR method showed no cross-reaction with Heterophyid flukes, it can be useful for specific identification of O. viverrini eggs in stool samples without the risk of false positives. It also has great potential for application in clinical epidemiological studies.

Liver fluke (Opisthorchiidae) findings in red foxes (Vulpes vulpes) in the eastern part of the Federal State Brandenburg, Germany--a contribution to the epidemiology of opisthorchiidosis

Parasitological examination of 677 livers from red foxes shot in connection with a rabies control programme were carried out in the eastern districts of the Federal State Brandenburg/Germany in 1996. Of the foxes, 32.5% were positive for opisthorchiid flukes. Metorchis bilis, the most frequently occurring fluke was found in 28.1% of foxes with numbers between 1 and 185. Opisthorchis felineus was found in 6.7% of fox livers. A maximum of 169 specimens was removed from one animal. Pseudamphistomum truncatum was present in only 2 foxes. The percentage of positive foxes in different districts varied between 15.8 and 43.3%. Significant differences in fluke prevalence were found between districts with a high share of surface water compared with a district with a low percentage of surface water. No sex-dependent differences in opisthorchiid prevalence were established.

Application of hazard analysis critical control point (HACCP) as a possible control measure for Opisthorchis viverrini infection in cultured carp (Puntius gonionotus)

Opisthorchiasis due to Opisthorchis viverrini and transmitted through infected freshwater cyprinoid fish (carps) affects more than 8 million people in Thailand, People's Democratic Republic of Lao, and Vietnam. The Hazard Analysis Critical Control Point (HACCP)-concept has been recommended by FAO and WHO to be included in programs to control foodborne trematode infections (FBT). HACCP is a multifactorial approach to control food hazards through surveillance of diseases, foods, and operations and education. This study describes the first attempt to apply HACCP to the prevention and control of Opisthorchis viverrini in pond culture carp (Puntius gonionotus). The experiment was designed and carried out by a multidisciplinary "HACCP team" including experts in the field of public health, parasitology, epidemiology, aquaculture, fisheries extension and fish inspection. The investigation was performed in two fish ponds in the District of Sun Pa Tong, Chiang Mai, Thailand. In the experimental pond, fish was cultured according to HACCP principles and compared with the control pond, which followed conventional aquaculture practices. Water supply to the pond, fish fry, fish feed and pond conditions during the growing period were identified as critical control points (CCPs). Hazards were identified and analyzed, as well as control measures, critical limits, monitoring procedures, corrective actions, and record keeping developed for each one of the above CCPs. Complete pond preparation, particularly aiming to eliminate contamination of pond water with O. viverrini eggs, fish infected with parasite meacercariae and the first intermediate host (Bithynia spp), was conducted. After the pond was filled with water, O. viverrini metacercaria-free fry were released into the pond. The preliminary results obtained indicate that HACCP-based principles applied to carp pond culture could be used as a strategy to prevent and control O. viverrini. Further studies should be undertaken aiming to confirm these preliminary results.

Opisthorchis viverrini metacercaria in Thai freshwater fish

Examination for metacercaria in freshwater fish, the common intermediate hosts of Opisthorchis viverrini was carried out during 1992-1996. The 4-year survey of fish from markets in 14 provinces revealed that metacercariae of O. viverrini were found in fish from Udon Thani, Sa Kaeo and Prachin Buri Provinces; fish from Aranyaprathet district had the highest positive rates (25-28%). Fish from 12 provinces were found to be positive with heterophyid metacercariae, namely: Haplorchis pumilio, H. taichui, H. yokogawai, Stellantchasmus falcatus, Centrocestus formosanus and Haplorchoides cahirinus. It was also observed that the prevalence of O. viverrini metacercaria in fish decreased markedly during the last 10 years.

Seasonal variation of Opisthorchis viverrini infection in cyprinoid fish in north-east Thailand: implications for parasite control and food safety

Reported is the seasonal pattern of Opisthorchis viverrini metacercariae in cyprinoid fish in north-east Thailand. Samples of fish were collected in 1991-92 at monthly intervals from two areas-Khon Kaen Province, where the opisthorchiasis transmission rate was high, and Mahasarakham Province, where the rate was low. Metacercarial loads in both study areas had similar seasonal patterns. High burdens occurred in the late rainy season and winter (July to January) with low burdens during the summer (March to June). The average burden for Puntius leiacanthus in Khon Kaen was 1.68 metacercariae per fish (127.43 per kg), higher than for all species of cyprinoid fish from the low transmission area. The intensities of infection among P. leiacanthus and Cyclocheilichthys armatus collected in Mahasarakham were comparable, but lower than the intensity of Hampala dispar (0.75 metacercariae per fish) concurrently sampled from the same area (P < 0.05). There was no significant difference in metacercarial load per kg between fish species from Mahasarakham. The results indicate that seasonal variation in metacercariae was a common phenomenon in areas with both high and low endemicity of infection. Also, the metacerarial load in fish was positively associated with infection levels among humans.

A focus of opisthorchiidosis in Germany

Epidemiological investigations were carried out in a focus of opisthorchiidosis in Brandenburg state of Germany. 9 out of 23 cats harboured adult flukes in their livers. Beside Opisthorchis felineus, Metorchis bilis was found in 4 cats. Muscle samples of 227 cyprinid fish belonging to 6 species (Rutilus rutilus, Scardinius erythrophthalmus, Alburnus alburnus, Abramis brama, A. ballerus, Blicca bjoerkna) were examined for trematode metacercariae. 12 different types of cysts were found. O. felineus was present in all fish species. R. rutilus and A. alburnus showed a prevalence of Opisthorchis of more than 70%. Two out of 166 Bithynia leachi were positive for trematode developmental stages. Due to their young age the rediae could not be specified.

[Opisthorchiasis and pseudamphistomiasis on the territory of the middle Volga valley]

The authors describe cases of opisthorchiasis and pseudamphistomiasis in 5 areas adjacent to the banks of the Volga, Kama, and Belaya. Metacercariae of Opisthorchis and Pseudamphistomum have been detected in the Cyprinidae. The incidence rate of Opisthorchis infection has been notified in these areas since 1957 and that of Pseudamphistomum infection has been recorded since 1989.

[A clinico-epidemiological study of opisthorchiasis in the Altai Territory]

Eighty-eight patients with opisthorchiasis were treated with biltricide in an anthropurgic and natural focus of opisthorchiasis in the Altai Territory. A one-day course of drug therapy, in a total dose of 60 mg/kg, was administered. Forty-two patients developed side effects in the course of therapy. Complete elimination of the helminths was achieved in 83 (94.3 +/- 2.3%; p less than 0.05) patients in 6 months after therapy.

[An assessment of the situation regarding opisthorchiasis in the area of the Irtysh-Karaganda canal]

The opisthorchiasis situation in Irtysh--Karaganda canal zone were studied. 615 men (by coprological method), 319 men (by serological method), 26 domestic cats, and molluscs (gen. Codiella)--were investigated. In the canal zone the situation of opisthorchiasis infection at present is favourable. Some of the infections are connected with the fish out of Shiderty River.

Human Opisthorchis and Haplorchis infections in Laos

A study of the epidemiology of trematode infections was carried out in Vientiane province, Laos, comprising examination of snails, fish, cats, and human stools. Opisthorchis viverrini cercariae were found in the snail Bithynia siamensis goniomphalus (Bithyniidae) and Haplorchis taichui cercariae in Tarebia granifera (Thiaridae). O. viverrini metacercariae were recorded in the flesh of 7 species of cyprinid fish; metacercariae of the heterophyid fluke Haplorchis taichui were found in 4 species of cyprinid fish and those of H. pumilio in 2 species. Cats from the same localities were infected with O. viverrini and 4 species of heterophyid flukes, frequently as multiple infections. The highest prevalence of small fluke eggs in human stools was recorded in the 20-29 years age group, particularly in males (90.4%). Three-quarters of human infections were light (less than 1000 eggs/g), the highest value (2975 eggs/g) being recorded in the 10-14 years age group. Identification of small flukes excreted by Laotian patients after treatment with praziquantel in Czechoslovakia revealed more cases with H. taichui than with O. viverrini. The results confirmed the simultaneous occurrence of O. viverrini and intestinal heterophyid flukes in the area studied.

[An assessment of the opisthorchiasis situation in the area of Irtysh-Karaganda Canal]

Helminthological investigation of the Irtysh-Karaganda Canal area was performed in the summer of 1989. In 9 storage ponds on the Shiderta and Olenta rivers 900 fish individuals, whose size was suitable for fishery have been examined, samples of water have been taken and the epidemiological assessment of modern conditions of opisthorchiasis agent circulation have been presented. The whole canal is at present favourable in view of opisthorchiasis infection. Local cases of infection are associated with fish from Shiderta and Olenta rivers.

[The detection of opisthorchiasis foci in Byelorussia]

Local foci of opisthorchiasis have been established on the territory of 3 Belorussian districts (Brest, Gomel and Grodno provinces). Human beings, cats, fish and the first intermediate host mollusk invaded with Opisthorchis have been found.

[The opisthorchiasis situation in the Kama-Vyatka river basin]

Geographic vicinity, common economy and connections between Kama and Vyatka river basins require systemic opisthorchiasis studies in these Ural areas. Literary data show that the situation with opisthorchiasis on the Kama River is mainly studied in Komi-Permiak Autonomous Okrug and is unclear in the upper Kama, in Kirovsk Province. Additional data have been obtained and opisthorchiasis was for the first time found in the population, cats and mollusks in the upper Kama, in Kirovsk Province. Opisthorchiasis foci were for the first time discovered on the Vyatka River. The level of cat and fish invasion in the upper Kama was higher than on the Vyatka River, which might be accounted for by ethnic peculiarities of the population on the Kama River.

Opisthorchis viverrini: finding and recognition of the fish host by the cercariae

The cercaria of Opisthorchis viverrini finds and recognizes its fish host by using at least four steps of behavioral patterns. (1) Dispersal and selection of plant-free water microhabitat are achieved by intermittent swimming behavior with positive phototactic orientation. (2) Attachment to the host is stimulated by water currents and a hydrophilic component of fish skin surface which has a molecular weight of more than 30,000. This component is sensitive to digestion with hyaluronidase and seems to be a glycosaminoglycan other than hyaluronic acid and chondroitin sulfate. (3) Remaining on the host's surface is induced by an unknown chemical component of fish skin surface mucus. (4) Penetration into the host is triggered by a hydrophilic component of fish skin surface of a molecular weight of more than 30,000. This host signal has a proteinaceus character as it is sensitive to proteinase digestion but not to hyaluronidase and glycosidases. The requirement of O. viverrini cercariae for complete glycosaminoglycans and proteins as signals in host identification may have the advantage that the numerous small molecules in mud and decaying materials in the water cannot interfere with host-finding.

[The structure of the geographic range of opisthorchiasis and the tasks in controlling this invasion]

Our own investigations in the Yenisei, Ob, Dnieper, Northern Dvina river basins and the analysis of the literary data served as the basis for establishing the relationship between the area of the pathogen dissemination and the area of opisthorchiasis distribution (the map scheme is attached). 4 degrees of endemicity characterized by quantitative indices of general affection, children's infestation, the invasion intensity and manifestation have been suggested as a criterion for division of territories into regions. The map of 3 territories in the Dnieper River basin (the Ukraine) most unfavourable for opisthorchiasis is presented. According to the endemicity, differential anti-invasion goals and measures are suggested.

[A comparison of the count of Opisthorchis in the body of the host and of the eggs eliminated with the feces]

The study of the intensity of Opisthorchis infestation by counting the amount of the parasites in the liver of 62 corpses and 12 cats and the quantity of the parasite's eggs per g feces was carried out. Furthermore, the number of the eggs depending on the intensity of the infection was counted. The fact of irregular distribution of eggs in the colon content and the lack of correlation between the quantity of parasites in the liver and egg contents per g was revealed. An increase in egg production in cases with severe pathology independent of its form was observed in spite of low intensity of invasion.