A prospective study of diet, lifestyle, and genetic factors and the risk of cancer in Khon Kaen Province, northeast Thailand: description of the cohort.

Cohort studies are the preferred design in observational epidemiology, but few involving the general population have been performed in Asia, and most concern affluent urban populations. The Khon Kaen study has recruited about 25,000 subjects, aged mainly 35-64, from villages in the relatively underdeveloped north-east of Thailand. All subjects underwent simple physical examination, completed an interviewer-administered questionnaire (including sections on lifestyle, habits, and diet) and donated specimens of blood, which were processed and stored in a biological bank at -20 degrees C. Female subjects (about 16,500) were offered screening by Pap smear, and specimens of cells from the cervix were stored at -20 degrees C. This paper describes the methodology of the study, and the characteristics of the participants. Almost all subjects are peasant farmers, with low annual income and body mass, although 14.6% of women had a BMI in the obese range (>30 kg/m(2)). Smoking was common among men (78% regular smokers, most of whom used home-produced cigarettes), but rare among women. Fertility levels were relatively high, with a more than half the women having four or more live births. 23.4% of subjects were infected with the liver fluke Opisthorchis viverrini, known to be highly endemic in this region. Follow-up of the cohort is by record-linkage to the provincial cancer registry. By 2003, 762 cancer cases had occurred, the most common being cancers of the liver (363 cases) and cervix uteri (44 cases). The antecedents of these cancers are being investigated using a nested case-control approach. The cohort will yield increasing numbers of cancers for study in the next decade, giving important information on the relative importance of dietary and lifestyle factors in a rural population, undergoing gradual transition to a more westernised lifestyle.

Prevalence of Opisthorchis viverrini infection and incidence of cholangiocarcinoma in Khon Kaen, Northeast Thailand.

Liver cancer is the most common cancer in Khon Kaen, Northeast Thailand, because of the high incidence of cholangiocarcinoma (CHCA). Opisthorchis viverrini (OV), a liver fluke, is endemic in the area, and has been evaluated as a cause of CHCA by International Agency for Research on Cancer. Residents of 20 districts in the province were invited to attend a mobile screening programme between 1990 and 2001. Of 24 723 participants, 18 393 aged 35-69 years were tested for OV infection, by examining stools for the presence of eggs. Prevalence of infection in each district was estimated from the sample of the population who had been tested. The incidence of liver cancer in 1990-2001 was obtained for each district from the cancer registry. The average crude prevalence of OV infection in the sample subjects was 24.5%, ranging from 2.1% to 70.8% in different districts. Truncated age-standardized incidence of CHCA at ages >35 years varied threefold between districts, from 93.8 to 317.6 per 100,000 person-years. After adjustment for age group, sex and period of sampling, there was a positive association between prevalence of OV infection and incidence of CHCA at the population level. Associations between CHCA and active OV infection in individuals have become hard to demonstrate, because of effective anti-OV treatment. The relationship may, however, be clear in comparisons between populations, which, for infectious diseases, take into account the contextual effects of group exposure in determining individual outcome. The cancer registry is an appropriate tool for disease monitoring in small areas.

The present situation of paragonimiasis in endemic area in Phitsanulok Province.

A cross-sectional survey and evaluation of paragonimiasis situation from endemic area in Phitsanulok Province was studied. Studies on the species and prevalence of parasites which infected people in Noen Maprang, Phitsanulok Province were also conducted during October 1999-March 2000. The sputum specimens were collected and examined to identify Paragonimus heterotremus eggs. In addition fecal samples were collected and examined for parasites by the formalin-ethyl acetate concentration technique. P. heterotremus eggs were detected in 2 out of 391 sputum specimens; a prevalence of 0.51%. A total of 584 stool specimens were obtained and examined. It was found that the prevalence of parasitic infection was 36.30%. Opisthorchis viverrini infection was the most prevalent (10.78%), followed by Strongyloides stercoralis (9.59%), hookworm (8.22%), Echinostoma spp (2.23%), minute intestinal flukes (1.54%), Taenia species (1.37%), Enterobius vermicularis (0.68%), Entamoeba coli (1.03%) and Giardia lamblia (0.86%). The prevalent rate of paragonimiasis in this endemic area in Phitsanulok Province has decreased during the past decade. However, there were other important parasite infections, especially opisthorchiasis and strongylodiasis and these should be studied further.

Seroprevalence of specific total immunoglobulin (Ig), IgG and IgM antibodies to Toxoplasma gondii in blood donors from Loei Province, Northeast Thailand.

A total samples from 345 healthy blood donors from Loei Province, Northeast Thailand were examined for anti-Toxoplasma gondii antibodies by ELISA. The seroprevalence of the anti-Toxoplasma gondii total Ig, IgG and IgM antibodies was 4.9%, 4.1% and 4.3%, respectively. Overall seropositive rate was 33 out of 345 individuals (9.6%). Among the seropositve cases, 5 (15.2%), 2 (6.1%) and 13 (39.4%) of the samples were determined by using each type of anti-T. gondii total Ig, IgG and IgM antibodies, respectively. The seropositive sera was also determined by combining of anti-T. gondii antibodies (anti-T. gondii total Ig with IgG and anti-T. gondii total Ig with IgM antibodies). These results were 10 (30.3%) and 2 (6.1%) cases, respectively. Only one (3%) sample had all types of anti-T. gondii antibodies. In addition, the frequency distribution curves of ELISA optical densities of anti-T. gondii total Ig, IgG and IgM antibodies in blood donor presented "unimodal" curves. The negative results were found in the age group that less than 20 years old and more than 51. The highest seropositive results were found in two age groups (21-30 and 31-40 years old), and males were significantly higher than female (p < 0.05). These results demonstrated that when using anti-T. gondii total Ig, IgG and IgM antibodies for determining the seroprevalence, the sensitivity was twice that with the anti-T. gondii, total Ig antibody alone.

Fasciola gigantica-specific antigens: purification by a continuous-elution method and its evaluation for the diagnosis of human fascioliasis.

Immunodominant antigens of an approximate molecular mass of 27 kD were obtained from an excretory-secretory product of adult Fasciola gigantica by a continuous-elution method. An indirect ELISA using the antigens obtained by this relatively simple procedure was developed for detecting specific antibodies from patients infected with F. gigantica. Sera from patients with other parasitic infections, healthy volunteers, and cholangiocarcinoma were also analyzed. The sensitivity, specificity, and positive and negative predictive values for this ELISA using the fractionated antigens were 100%. The data indicated a possible correlation of antibodies to F. gigantica with cholangiocarcinoma.

Specific gravity of Opisthorchis viverrini eggs.

The specific gravity of the eggs of the liver fluke Opisthorchisviverrini was determined using a sucrose gradient centrifugation and found to range from 1.2713 to 1.3043. The peak egg count was located at the sucrose fraction with a specific gravity of 1.2814. An attempt to float eggs in saturated sodium nitrate solution, sp.gr. 1.4, failed. Examination of human stool specimens for Oviverrini eggs by simple flotation in saturated sodium nitrate solution and the formol-ether sedimentation technique revealed that the flotation technique was not as efficient as the sedimentation technique. It was suggested that the flotation techniques were inappropriate for the detection of Oviverrini eggs in faeces or contaminated soil.

Studies on biting density and biting cycle of Culex quinquefasciatus, say in Khon Kaen City, Thailand.

Biting density and biting cycle of Culex quinquefasciatus in Khon Kaen City were examined during November 1994 to October 1995. Biting activity of the mosquito was assessed by using the indoor human bait method. Trapped mosquitos were identified and carefully dissected to determine their parities. Climatory data ie temperature, relative humidity and rainfall were also recorded during the study. The densities of mosquito ranged from 1.6/man/hour in December to 9.2/man/hours in March with the average of 5.0/man/hours. The lowest biting density was observed in winter and higher densities were in summer and rainy seasons. The temperature was the most important variable that influenced the biting density in each month of the year (p<0.05). The biting cycle showed that the mosquito active throughout the night, with peak activity at 22.00-23.00 hours. Parous rate of the mosquito ranged from 33.3% in February to 71.9% in November with the average of 47.3%. The biting proportion of parous mosquitos was high during the early hours of the night and gradually decreased until 06.00 hours, whereas that of the nulliparous mosquitos showed an increasing trend from 18.00 to 06.00 hours. The biting cycle of the parous mosquito reached the peak activity at 21.00-22.00 hours, 1 hour ahead of the peak for nulliparous mosquito. These findings suggested that Cx. quinquefasciatus in Khon Kaen City may be able to transmit bancroftian filariasis if they were exposed to microfilaria carrier individuals.

Excretory-secretory antigenic components of adult Fasciola gigantica recognized by infected human sera.

The immunogenic components of Fasciola gigantica excretory-secretory (ES) products were revealed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting technic using sera from patients with F. gigantica infection, from patients with clinical suspected fascioliasis, from patients with other illness and from healthy adults. By SDS-PAGE, it was found that the ES products comprised more than 6 polypeptides. Immunoblotting analysis revealed 12 components which were strongly recognized by fascioliasis antisera. These antigenic components had a molecular mass ranging from less than 14.4 to 38 kDa. One antigenic band of 27 kDa was found to give a consistent reaction with fascioliasis antisera (100% sensitivity and 98% specificity). The present findings suggest that the 27 kDa components are sensitive and specific for the diagnosis of human F. gigantica infection.

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.

PIP: Food-borne trematode infections such as Opisthorchis viverrini are a major cause of morbidity in Asia. Samples of cyprinoid fish collected at monthly intervals during 1991-92 in two provinces (Khon Kaen and Mahasarakham) in North East Thailand revealed substantial seasonal variation of O viverrini metacercariae. The former province is a low transmission area (29.7% average infection rate), while the latter is a high transmission area. Metacercarial intensity was highest from January-March 1991 and October 1991-April 1992, with maximum intensities during February and December 1991. Puntius leiacanthus fish from Khon Kaen bore the highest density of metacercariae per individual fish (1.68). Differences in the intensity of infection for the same species of fish captured in two different geographic areas presumably reflect variations in environmental conditions such as local levels of human and snail infections. Fecal contamination of the study reservoirs is greatest during the early parts of the rainy season as a result of run-off drainage and coincides with the rapid increase in snail populations. The optimal time for large-scale community-based parasite control programs is when the probability of rapid reinfection is lowest and the prevalence and intensity of infection in people are highest (e.g., April-June or the summer months). Most effective is a program that integrates parasite control, environmental management, health education, and food safety.

Angiostrongylus infections in rats and snails in northeast Thailand.

A survey of Angiostrongylus infections in rats and snails was carried out in the provinces of Ubon Ratchathani, Udon Thani. Kalasin, Chaiyaphum and Khon Kaen in northeast Thailand. Only two Rattus norvegicus (3.8%) and one Bandicota indica (1.4%) out of 151 R. rattus, 52 R. norvegicus and 69 B. indica examined were infected with adult lung worms. All worms recovered were A. cantonensis. Prevalence of infection in 423 Pila polita was 0.9% while all of 77 P. ampullacea were negative for larvae. In contrast to this 36.4% of 500 Achatina fulica harbored L3 of Angiostrongylus (with variations of between 29% and 46% in the five provinces). The average infection intensity in A. fulica was 13.6 L3 (1 to 441). Experimental infection of Wistar rats with L3 (isolated from A. fulica resulted in a recovery rate of 48.3% of adult worms of which 91.7% and 8.3% were identified as A. cantonensis and A. malaysiensis, respectively. This is the first proven finding of A. malaysiensis in northeast Thailand.

Morphology and ultrastructure of the digestive gland of Bithynia siamensis goniomphalus (Prosobranchia: Bithyniidae) and alterations induced by infection with the liver fluke Opisthorchis viverrini (Trematoda: Digenea).

The morphology and ultrastructure of the digestive gland of Bithynia siamensis goniomphalus and its alteration by infection with Opisthorchis viverrini were investigated by light and electron microscopy. The digestive gland of B. s. goniomphalus was composed of three different cell types: digestive cells, excretory cells, and narrow cells. In infected animals the number of excretory cells increased dramatically. Cellular injury in digestive cells as well as in excretory cells following the infection could be observed at the ultrastructural level.

Quetelet index, hemoglobin and parasitic infection of rural women in northeast Thailand.

The Quetelet index, hemoglobin and parasitic infection rates of adolescent and young women from 21 villages in Northeast Thailand were assessed. Data were collected in the hot, rainy and cold seasons of the year. The proportion of undernourished females varied between 10 and 15% when a cut-off point of 18.7 of the Quetelet index was chosen. 23 to 33% of the women had hemoglobin levels below 12 g%. Parasitic infection rates with various intestinal helminths were high but not related to the nutritional status or anemia.

Opisthorchiasis control in northeast Thailand: proposal for a new approach.

Opisthorchiasis, i.e. infection with the liver fluke Opisthorchis viverrini is an important health problem in Thailand and adjacent Laos, and its control is therefore of high priority. Pilot projects have shown that after praziquantel treatment high re-infection rates occurred within a short period of time. To reduce re-infections it is proposed to couple the time of treatment to the seasonal transmission dynamics and thus treat the population in March when risk of infection for the snail and fish intermediate and the human definitive hosts is lowest. Adjustment would save costs and time.

Increased nitrosamine and nitrate biosynthesis mediated by nitric oxide synthase induced in hamsters infected with liver fluke (Opisthorchis viverrini).

We previously reported that increased endogenous nitrosation in human subjects infected with the liver fluke Opisthorchis viverrini in north-east Thailand could be a risk factor for the development of cholangiocarcinoma. In the present study we examined our hypothesis that this increased endogenous nitrosation is mediated by nitric oxide (NO) synthase induced by O. viverrini infestation. Syrian golden hamsters experimentally infected with O. viverrini liver fluke excreted in the urine significantly greater amounts of nitrate, a stable oxidization product of NO, than untreated hamsters (3.64 +/- 0.86 versus 2.64 +/- 0.60 mumol/hamster/day, P < 0.001). When the rapidly nitrosatable thiazolidine 4-carboxylic acid was administered orally, the infected hamsters also excreted significantly elevated levels of N-nitrosothiazolidine 4-carboxylic acid than untreated hamsters (4.27 +/- 2.20 versus 2.33 +/- 1.13 nmol/hamster/day, P < 0.01), indicating that endogenous nitrosation is elevated in the animals with liver fluke. NO synthase activity measured in liver cytosol was about twice as high in the infected hamsters as in untreated animals. The enzyme, whose biochemical characteristics were similar to that induced in activated murine macrophages, was immunohistochemically localized in the cytoplasm of macrophages and eosinophils in the inflammation zone surrounding the parasite-containing bile ducts. These results support our hypothesis that, in fluke-infected subjects, NO synthase induction leads to excess production of NO and the observed elevated endogenous nitrosation. Since high concentrations of NO exert cytotoxic and mutagenic effects per se, excess NO produced in chronically infected/inflamed tissues may also play a role in initiation and subsequent modulation stages of cholangiocarcinoma development.

Studies on lophocercous cercariae from Bithynia siamensis goniomphalus (Prosobranchia: Bithyniidae).

Cercariae from Bithynia siamensis goniomphalus were studied in an area endemic for opisthorchiasis. Snails emitted different types of cercariae when shedding was induced by illumination. In addition to two lophocercous cercariae, a monostome cercaria (probably Notocotylus sp), two different furcocercariae and a xiphidiocercaria were found. Two similar types of lophocercous cercariae were distinguishable and one could be identified as Opisthorchis viverrini. To date the cercaria of O. viverrini has been regarded as the only lophocercous cercaria in the endemic area of opisthorchiasis. Therefore, differences between these cercariae were further characterized by scanning electron microscopy to enable us to avoid misinterpretations of O. viverrini in Bithynia.

Studies on metacercariae from naiads in northeast Thailand.

One hundred and eleven naiads from six different dragonfly species were investigated for the presence of metacercariae. Sixty-nine animals (62.2%) were infected with intensities up to more than 150 cysts per animal. The metacercarial cysts were characterized by light and scanning electron microscopy. Two types of metacercariae could be differentiated by morphological features of cyst surface, cyst wall and size.

Field trials in the control of Opisthorchis viverrini with an integrated programme in endemic areas of northeast Thailand.

A control programme of opisthorchiasis was carried out for three years in three villages of northeast Thailand in order to compare the effectiveness of two intervention measures. The intervention measures employed were to give praziquantel treatment to all infected people either once (village I) or twice (village II) per year with the integration of regular health education and sanitation improvement. A control village (village III) received no intervention during the study. Sampling of the population in these villages to estimate prevalence, intensity, reinfection and incidence of infection as well as knowledge of opisthorchiasis and number of latrines was performed at 6 monthly intervals throughout the duration of the study. At the initial assessment, there were no significant differences in the prevalence and intensity of infection of villages I and II. Both values were greatly reduced when assessed 6 months after the initiation of treatment, and the decrease in prevalence and intensity of infection did not differ between village I and II. The control village (village III), during the first 2 years, exhibited slight variation in the prevalence and intensity, and these decreased considerably in the third year of the study. The reinfection rate per 6 months in villages I and II was nearly equal. The incidence rate per 6 months in the two treated villages was lower than that of the control village. Marked improvement in knowledge of opisthorchiasis, behavioural changes of eating raw fish and increased numbers of latrines was evident in all of the villages during this study.(ABSTRACT TRUNCATED AT 250 WORDS)