Opisthorchis viverrini: relationships between egg counts, worms recovered and antibody levels within an endemic community in northeast Thailand

Three techniques for estimating the intensity of Opisthorchis viverrini infection in individuals from a Northeast Thai community are compared. Egg counts were determined using a quantitative formalin/ethyl acetate technique, worm burdens were estimated by expulsion chemotherapy and antibody levels were measured by ELISA. Log-transformed worm and egg counts were closely correlated (r = 0.80), suggesting that both measurements provide good assessments of relative intensity of infection. However, no Opisthorchis worms were recovered from 34 people with high egg counts; probably due to problems with the expulsion technique in some individuals. Examination of egg production per fluke indicated that each fluke contributed an average of 180 eggs per gram (epg) of faeces and fecundity was negatively associated with total worm burden. Serum IgG levels correlated significantly with Opisthorchis egg count (r = 0.61) at two independent assessments. Although significant associations were observed between antibody levels and echinostome infection, analysis suggested that these reflected independent associations between these two variables and Opisthorchis infection and age. We conclude that all three measurements are useful for epidemiological studies.

[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.

Detection of Opisthorchis viverrini by monoclonal antibody-based ELISA and DNA hybridization

Monoclonal antibody-based enzyme-linked immunosorbent assay and DNA hybridization techniques were developed and evaluated for their potential in the detection of Opisthorchis viverrini infection in humans. A mixture of three IgG1 monoclonal antibodies (MAb) specific for the 89 kDa metabolic product of O. viverrini was captured on a microtiter plate by rabbit anti-mouse IgG and used in a sandwich ELISA for the detection of parasite antigen. The 89 kD component bound to the MAb was detected with biotinylated rabbit IgG antibody to O. viverrini metabolic products. As little as 0.05-0.1 ng of the antigen could be detected by this technique. A specific O. viverrini DNA probe constructed from a repetitive DNA segment containing 340 base pairs was used in a dot blot hybridization for the detection of parasite DNA. The labeled probe constructed as such could detect DNA released from as few as five O. viverrini eggs. Both methods were specific for O. viverrini and their sensitivity was comparable with that of the classical parasitological technic.

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 decreased susceptibility of Syrian hamsters to Opisthorchis felineus invasion after its repeated administration]

The investigations conducted on Syrian hamsters have revealed that multiple enteral infusions of cold inactivated (t = -10 degrees C) O. felineus metacercariae resulted in the formation of immunocompetent cell and fibroblast infiltrations around the branches of the portal vein. The infestation of animals by viable pathogens led to reduced accommodation of helminths and suppressed cell infiltration in the liver. It is assumed that the native population of the foci become tolerant to the disease with the penetration of noninvasive Opisthorchis larvae into their body and the development of latent forms of helminthiasis.

Fecal egg output in relation to worm burden and clinical features in human opisthorchiasis

A study of the relation of fecal egg excretion to worm burden and clinical features was carried out in 45 opisthorchiasis patients who had no signs of biliary obstruction. The fecal egg excretion was consistent and correlated with the worm burden. Although there was no definite association between clinical signs and intensity of infection, mild hepatomegaly and thickened wall or dilatation of the gallbladder were found more commonly in heavily infected patients. Eosinophilia was observed more often than previous reports. Concomitant parasitic infections were found in 82% of the patients. After praziquantel treatment, egg counts increased greatly during the first few days then decreased to very low levels in 7 days.

[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.

[Opisthorchiasis, the pancreas and diabetes mellitus]

The authors reviewed the data on pathogenesis, pathomorphology and clinical appearance of the incretory pancreatic involvement in opisthorchiasis patients. Besides, the authors presented their own data on the impact of opisthorchiasis invasion on the formation of diabetes mellitus. The concept of a diphasic involvement of the insular system was considered.

[The effect of anthropogenic transformation on the conditions for the circulation of the causative agent of opisthorchiasis]

The conditions of O. felineus circulations in the area of minor hydraulic constructions of Graĭvoron on the Vorskla River where a tense Ukrainian focus of opisthorchiasis existed (the village of Dobryanskoye, Sumy Province) were followed up for a 8-year period (since 1982). Hydraulic construction near the Vorskla River resulted in a significant violation of the ecological balance (macrocyte occupation of the river bed and the bay terrace, bog-making, dystrophic changes of the low-land bodies of water). The aforementioned circumstances influenced the conditions of O. felineus circulation (decreased number of Codiella mollusk habitats, decreased density of the mollusks and their invasion rate with larvivorous forms of Opisthorchis, lower invasion rate in carps). The considered processes are now characteristic of many minor rivers in the Ukraine. Though their negative impact on the ecological conditions causes no doubt it should be taken into account and used for the eradication of Opisthorchis foci (in combination with therapeutic and sanitary education measures).

[The current status of the Turgai focus of opisthorchiasis]

Complex investigations in the Turgai opisthorchiasis focus stated that it is characterized by weak intensity of the epidemic process, as evidenced by stable low morbidity index (5.5%) and invasion intensity of population, the average number being 4.968). The fact is mainly due to the natives' daily habit to use fish that is heat-treated. Meanwhile, the risk infection in the focus is rather great, for there is considerable fish invasion in the Turgai River with Opisthorchis larvae and 40% of cats are infected with Opisthorchis.

[Fishes in the lower reaches of the Ob River studied for their infectiousness with helminth larvae of medical significance]

The data on fish infection with Diphyllobothrium and Opisthorchis larvae in the lower Ob were specified. There is a tendency to decrease fish infection with Diphyllobothrium plerocercoids and preserve infection with Opisthorchis metacercariae.

[The role of the owsianka Leucaspius delineatus in maintaining opisthorchiasis foci in Novosibirsk Province]

Materials reflecting opisthorchiasis infection in fish in the Novosibirsk region were analyzed. On the basis of fish population estimation and studies on its invasion with Opisthorchis felineus (Rivolta, 1884) it was shown that a considerable part in maintaining opisthorchiasis foci is played by Leucaspius delineatus. It is numerous, can easily acclimatize itself in natural water bodies, inaccessible for predatory animals, easily infected with Opisthorchis larvae, and therefore can play an important role in formation of new opisthorchiasis foci during amelioration of Kulunda and Baraba forest-steppe.

[Helminthiases among the population of northwestern Siberia. 1. Opisthorchiasis and mixed invasion in the native inhabitants of the Ob River basin and their clinical course]

The use of multifactor statistic analysis for screening population of the northern part of the Ob river basin for helminthiasis allowed the authors to reveal a significant feedback between manifested opisthorchiasis and other types of this disease course in both sexes. The main component analysis indicates that the tentatively control group of males is presented by adolescents (14-17 years old) who are likely to be infected with Opisthorchis without evidence of its clinical manifestations. The correlation analysis demonstrated also a direct relationship between the age and manifest opisthorchiasis, as well as double mixed invasion of males (r-0.15 and 0.26, p less than 0.05 and 0.01, respectively). The first three main components explain about 55% variance in the correlation matrix of initial parameters and allow to reveal the variance source, taking into account, along with differentiation of 4 groups of opisthorchiasis patients, also the age- and sex-dependent combination of opisthorchiasis with other helminthic invasions.

[Comprehensive assessment of an opisthorchiasis focus in the Komi-Permiak Autonomous Okrug]

Unfavourable sanitary and hygienic conditions in 2 settlements have been established; the authors revealed specific features of the invasion spreading in this focus where high invasion rates of intermediate and final hosts were associated with low invasion rates. Different factors have been established, which contribute to the invasion spreading among the population. A three-score assessment has been proposed of the manifestations of the clinical symptomatology in digestive disease in opisthorchiasis which is suitable for in the field. A retrospective analysis has been made of the reasons for ineffective chemotherapy with chloxyl in this focus. The age-related affliction with opisthorchiasis in the focus is the most adequately described by a "reversible catalytic" model with a force of infection of 0.055.

[Seroepidemiologic characteristics of opisthorchiasis foci with various endemic levels]

Combined coprological (by an ether-formol method) and serological (by solid-phase enzyme immunoassay--EIA) screening of the population to detect opisthorchiasis was performed in the settlements situated in the Ob, Dnieper and Northern Dvina basins. Disease rate in the hyperendemic area on the Ob exceeded 80%, by the results of coprological population screening, while annual infestation rate established on the basis of specific antibodies determination in the blood was 70%. Infestation and disease rates in mesoendemic area, at the Ob tributary and in the Dnieper basin were practically equal and accounted for 30-40%. Infestation rates in hypoendemic areas of the Dnieper and Northern Dvina basins exceeded those of the disease rate. Causes of this phenomenon are discussed. Double serological screening of population in the foci performed in summer-autumn and spring seasons demonstrated a considerable increase in infestation rate parameters in autumn and their decrease in spring. Seasonal character of infestation is better expressed in the mesoendemic areas than in the hyperendemic ones. Infestation and disease rates are discussed for various age groups in different areas.

[Susceptibility of Bithynia inflata mollusks from discrete populations for Opisthorchis felineus infestation from different foci of opisthorchiasis]

Experiments were conducted on crossed infection of the specific intermediate host of Opisthorchis, molluscs of Bithynia inflata from different and remote populations, with eggs of O. felineus from different nidi of the disease. The strains of the agent were found to be heterogeneous that is expressed in different degree of compatibility with the intermediate host.

[Heterogeneity of populations of the mollusc Bithynia inflata according to the degree of trematode infestation in opisthorchiasis foci]

Results of studies of differences in the infection rate of natural populations of Bithynia inflata with trematodes (including Opisthorchis felineus) in the nidi of opisthorchiasis in the Sumsk and Chernigov Districts of the Ukrainian SSR and Tomsk District of the RSFSR are given. It has been shown that in the Ukrain over 1/3 of all populations of the specific intermediate host of opisthorchis does not take part in the circulation of the agent due to fundamentally different reasons: resistence to the infection and hyperinfection with parthenites of trematodes.

Hemobilia and liver flukes in a patient from Thailand

A patient from Southeast Asia presented with abdominal pain, fever, jaundice, and upper gastrointestinal bleeding of unknown origin. Opisthorchis viverrini eggs were found in the stool and multiple hepatic filling defects were noted on liver scan and sonogram. Endoscopic retrograde cholangiopancreatography revealed cholelithiasis and crescent-like filling defects in the biliary system. At surgery, the gallbladder was filled with clotted blood and pigmented stones. During T-tube drainage of the common bile duct, small elliptical flukes (4 X 3 mm) identified as O. viverrini were recovered. Despite adequate biliary drainage, the patient continued to have high fevers. On the 53rd postoperative day, a larger fluke (2.8 X 0.8 cm) identified as a Fasciola hepatica migrated down the T-tube. Institution of therapy with bithional resulted in complete clinical resolution within 3 wk. Six years later the patient returned with fever, jaundice, and right upper quadrant pain. Two large pigmented stones were found in the common bile duct and were removed after endoscopic sphincterotomy. The stones had developed even though there was no evidence of recurrent helminthic infection.

Treatment of Opisthorchiasis viverrini in hamsters with albendazole

Efficacy of many drugs against Opisthorchis viverrini in man were shown by the percentages of egg reduction and the absence of egg in faeces. In some cases, however, the eggs reappeared after a period of time. The pathological changes of the bile duct could cause partial or even complete obstruction of the bile passages, thus resulting in the occurrence of natural egg reduction. Albendazole, a broad spectrum anthelmintic was used to treat opisthorchiasis viverrini in hamsters. At dosage of 100 mg per kg body weight twice daily for three consecutive days, the drug yielded an average of 81.5% of worm reduction at four months after medication. In this study complete cure was not obtained.

Evaluation of selected anthelmintic compounds for activity against Opisthorchis viverrini

In vitro and in vivo experiments were employed in the screening of potential anthelmintic agents against Opisthorchis viverrini infection in hamsters. A few selected groups of compounds tested included those that are commercially available as well as those that are still being tested by various pharmaceutical firms. The compounds tested in the present study were praziquantel, amoscanate, albendazole, flubendazole, metrifonate, metronidazole and benzodiazepine derivatives. Results from both in vitro and in vivo experiments showed that at the dosages employed, praziquantel was the only one that gave complete cure, as judged from faecal egg examination and worm recovery at the time of sacrifice. It was therapeutically effective against different developmental stages of O. viverrini including the metacercariae. Moreover, the drug was also effective as a chemoprophylactic agent when given 6 to 12 hr prior to being exposed to infective metacercariae. Other compounds tested were considerably less active although some might have permanently damaged the fluke reproductive capacity, while others were able to suppress egg-laying capacity only temporarily. Together, results suggests that the ineffectiveness of most agents tested in this study is not related to their inability to attain concentrations high enough to kill or damage the flukes in the biliary system but is most likely due the inherent lack of capacity to kill the flukes.

Alterations of the surface tegument of Opisthorchis viverrini exposed to praziquantel in vitro and in vivo

The in vitro and in vivo effects of praziquantel on the ultrastructural surface of Opisthorchis viverrini were investigated using scanning electronmicroscopy. For the in vitro study, adult flukes were collected from experimentally infected hamsters, and were incubated for various time intervals at 37 degrees C in Earle's basal medium containing praziquantel at final concentrations of 0.01-100 micrograms/ml. For the in vivo study, flukes were collected from the biliary system of experimentally infected hamsters that had been treated 4 hours previously with 350 mg of praziquantel per kg body weight (mg/kg). Flukes were also obtained from the feces of a patient with opisthorchiasis who had been given praziquantel once at a dose of 40 mg/kg 4-6 hours previously and from the bile of a patient at the time of operation 24 hours after praziquantel treatment. Scanning electronmicroscopic analyses of the surface teguments of flukes exposed to praziquantel either in vitro or in vivo showed similar changes. Tegumental bubbles of different sizes appeared on the surface; they later ruptured and resulted in the formation of crater-like lesions. These lesions might be so extensive as to result in the peeling of the entire areas. On occasions, "micronodules" appeared later in these areas and those at the periphery of the lesions; these micronodules may represent an attempt by the worm to regenerate new tegument. The possibility that these ultrastructural changes may represent a generalized response of the tegumental surface to an obnoxious agent was discussed.

Consistency of fecal egg output in patients with Opisthochiasis viverrini

Counts of Opisthorchis eggs in two samples of feces arbitrarily taken 0-21 days apart from each of 209 patients from northeastern Thailand were carried out by Stoll's dilution technique. Based on the number of eggs/mg feces, each patient was classified as uninfected, lightly infected (less than 1 egg/mg), moderately infected (1-10/mg), heavily infected (greater than 10-50/mg), or very heavily infected (greater than 50/mg). The intensity of infection for each of the 209 individuals as shown by first and second counts was compared. Of the 209 individuals, 150 (71.8%) remained within the same egg excretion category, with all but five (2.4%) of the remainder being in an adjacent category. Statistical analysis showed no effect of variation in interval between stool counts on the accuracy or consistency of replicate counts.

Opisthorchis viverrini: life cycle, intermediate hosts, transmission to man and geographical distribution in Thailand

Opisthorchis viverrini has been found to be the only species of liver fluke in Thailand. The morphology is similar to that of O. felineus, but it has more deeply lobated testes, situated near the ovary. The appearance and distribution of the vitellaria with few granular clumps and the shorter and wider egg closely resemble that of C. sinensis. The adult worms live in the biliary system. Eggs pass out in faeces. On reaching water the eggs are eaten by snails, the first intermediate host. In the snail the miracidia hatch and develop further through the stages of sporocysts, rediae and cercariae in six to eight weeks. The cercariae then leave the snail, penetrate into susceptible fresh water fish, encyst in the muscle and develop into metacercariae, and infective stage, in six weeks. When ingested by man or animal the metacercariae excyst in the duodenum or jejunum and then migrate to the bile duct. They become mature within four weeks and begin to produce eggs. The life span of the fluke is over 10 years. The snail intermediate hosts are Bithynia goniomphalus, B. funiculata and B. siamensis. Many species of cyprinoid fish serve as second intermediate host; Cyclocheilichthys siaja is the most important. Cats, dogs and many fish eating mammals are definitive hosts. Man and animals acquire infection by eating raw fish containing metacercariae cysts. In Northeast Thailand "Koi-Pla" is the most popular raw fish dish. In 1980-1981 the prevalence in the north, northeast, centre and south of Thailand was 5.59, 34.60, 6.34, and 0.01%, respectively, with an overall prevalence of 14% or 7 million people.

Opisthorchis viverrini infection: pathogenesis and clinical features

The pathological changes are more or less related to the intensity and the duration of the infection, and are commonly seen in older patients with a large number of flukes. The pathogenesis is due to the mechanical irritation by the flukes and some toxic substances produced by them. Lesions are mainly confined to the biliary system. There is hyperplasia of the epithelial cells lining the bile ducts. In heavy and severe infections there are obstruction of the biliary tract, bile retention, extensive hyperplasia of the biliary system, with glandular proliferation of papillomatous and adenomatous type, cholangitis, periductal infiltration with eosinophils, round cells and fibrosis in the portal areas, necrosis and atrophy of hepatic cells. The bile ducts are dilated and in late cases saccular or cystic formations may develop into large cysts. The gallbladder may enlarge and contain white bile. The liver profile is generally normal. The majority of cases are symptomless. Clinical features vary from mild to severe. The symptoms and signs are vague gastro-intestinal symptoms, flatulence, anorexia, lassitude, weight loss, dull pain at the right hypochondrium, hot cutaneous sensation of the abdomen, and enlargement of the liver with some tenderness. In few cases the manifestations are severe. There is relapsing cholangitis, the patient is seriously ill and may succumb to septic shock. Cholangiocarcinoma, gallstones and obstructive jaundice are not unusual associations.

Opisthorchis viverrini: the relationship between egg production, worm size and intensity of infection in the hamster

Worm recoveries, egg production and worm lengths were determined in golden Syrian hamsters given between five and 200 Opisthorchis viverrini metacercariae. Animals given five, 10 or 20 metacercariae showed similar worm recovery rates of 38%, 36% and 37%, respectively, whereas animals given 50, 100 or 200 metacercariae gave recoveries of 49%, 65% and 54%, respectively. The distribution of worms between right, left and middle liver lobes was similar for animals with between one and 43 worms but different for animals with between 64 and 154 worms. A curvilinear relationship between eggs found per gram of faeces per worm (epg/worm) and eggs/worm/24 hours and worm burden was observed at 60 days post-infection, with worm egg output decreasing as worm burden increased. Regression analysis of the logarithmically transformed data gave regression coefficients of r = 0.62 for log 10 epg/worm v. worm burden and r = 0.71 for log 10 eggs/worm/24 hours v. worm burden. When the same analyses were performed substituting worm density (worms/gram liver tissue) for worm burden, little or no difference was seen in the correlations obtained. A similar relationship was also observed between worm length and worm burden with mean worm length appearing to decrease with increase in worm burden. These results clearly show that worm crowding in the hamster host can have a profound effect on worm egg output and growth. The possible mechanisms underlying these phenomena are discussed and their potential relevance in human opisthorchiasis considered.

Morbidity in relation to intensity of infection in Opisthorchiasis viverrini: study of a community in Khon Kaen, Thailand

A study of the prevalence and intensity of opisthorchiasis viverrini in relation to morbidity as determined by standard medical examination was carried out in Nong Ranya, a small village containing 309 people in northeastern Thailand. Opisthorchis viverrini infection as determined by Stoll's quantitative egg count method had an overall prevalence of 94% and reached 100% prevalence in most age groups above the age of 10 years. With respect to intensity, 6% were uninfected, 26% had light (less than or equal to 1 eggs per mg [epmg] of feces), 37% moderate (greater than 1-10 epmg), 25% heavy (greater than 10-50 epmg), and 5% very heavy (greater than 50 epmg) infections. Peak intensity in both males and females occurred at age 40 and above. A history of eating "koipla" (a sauce consisting of ground up raw fish), of feeling weak, and of having right upper quadrant abdominal pains occurred most frequently in the infected groups and was correlated with intensity of infection. Regardless of intensity of infection, only a small proportion of the population were unable to carry out their routine activities. Anorexia, nausea or vomiting bore little relationship to the presence or intensity of infection. Hepatomegaly at the mid-clavicular line occurred in 14% of the population, mainly in the more heavily infected groups. Neither jaundice nor splenomegaly was observed in the population.