The prevalence of viral hepatitis among the Hmong people of northern Thailand.

Sera from 269 Hmong people (102 males and 167 females, with mean age 35.4 years, range 16-63 years) were examined in order to determine the seroprevalence of hepatitis virus infection. The seroprevalence rates for HAV (hepatitis A virus), HBV (hepatitis B virus), HCV (hepatitis C virus), HDV (hepatitis D virus), HEV (hepatitis E virus), HGV (hepatitis G virus) and TTV (TT virus) infection were 87.8% (n=140), 76.0% (n=150), 2.0% (n=150), 0.7% (n=150), 6.5% (n=139), 5.3% (n=94) and 25.6% (n=121) respectively. The rate for carriers of HBV (HBsAg) was 13.8% (20.5% in males and 9.6% females) with a peak prevalence in the 21-40 year age group. A high rate of HAV seropositivity was found among the younger subjects. The rate of HEV seroprevalence was low. The prevalence of TTV-DNA was high with no difference between the sexes. HGV-RNA prevalence was low and seen primarily in males. This study indicates that the Hmong people are endemically infected with HAV and HBV infection and should be considered for targeted vaccination. The role of TTV and HGV in producing illness and hepatic disease has yet to be determined in this population.

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.

Feasibility of northern Thai factory workers as participants in HIV vaccine trials.

To determine the feasibility of establishing a cohort of HIV-1 seronegative factory workers for potential HIV vaccine trials, and other HIV preventive interventions, we enroled and followed 499 male and female industrial workers in Lamphun Province, northern Thailand. A baseline demographic and HIV seroprevalence survey was conducted by a mobile team at worker's housing units in Lamphun Province in 1994. Follow-up HIV and syphilis incidence rates were measured 6 months later. The study was voluntary, anonymous, and included HIV pre- and post-test counseling, HIV and syphilis serology, and a self-administered fact sheet. A total of 106 men and 393 women were recruited. The median age was 22 years, and the mean 23.4 years. Educational levels were moderate; 41.9% had some secondary school and 23.6% had completed secondary school. HIV prevalence was 2.4% overall but differed by sex; among men it was 7/106, 6.6%, among women 5/393, 1.3%, OR = 5.49 (95% CI = 1.52, 20.39). Low educational levels were associated with HIV infection, OR = 7.2 (95% CI = 2.2, 23.4). Syphilis prevalence was 3.8%. Follow-up at 6 months was successful for 420/499 subjects, 84.2%, and varied by sex: 73/106 men, 68.9%, returned while 347/393 women, 88.3%, did so, RR = 1.21 (95% CI = 1.07, 1.37). There were 5 incident HIV-1 infections, a rate of 2.1/100 person years. The HIV seroconversion rate differed by sex, but not significantly; it was 4.1/100 person years for men and 1.5/100 person years for women. This population is largely young, female, and at considerable HIV risk. If follow-up could be improved, factory workers in northern Thailand could be an appropriate population in which to mount HIV preventive efficacy studies, including vaccine trials.

Serosurveys of spotted fever and murine typhus in local residents of Taiwan and Thailand compared with Japan.

To estimate the prevalence of spotted fever (SF) and murine typhus (MT) rickettsioses in Southeast Asia, we performed serosurvey by immunoperoxidase test on local residents in Taiwan and Thailand, comparing them with those of Japan. In Japan, the prevalence of antibodies (1:80 as cut-off level) to some SF/MT antigens was noticeable in Japanese SF-endemic areas or a high-risk groups. In Tainan, Taiwan, SF antibodies were not so prevalent (3.5 to 4.4%), but MT antibodies were more prevalent (23.9%). In Chiang Rai in northern Thailand SF antibodies were markedly prevalent (9.0 to 21.3%); the reactivity with Thai tick 118 strain alone was 8.2%, but MT was less (2.5%). These results suggest that these rickettsioses may be latently distributed in various parts of Asia.

Comparison of cysticercus extract, cyst fluid and Taenia saginata extract for use in ELISA for serodiagnosis of neurocysticercosis.

Cysticercus cellulosae extract (CS), cyst fluid (CF), and an extract of Taenia saginata adult worm (TS) were evaluated for use in an enzyme-linked immunosorbent assay (ELISA) for serodiagnosis of human neurocysticercosis in Thai patients. ELISA sensitivity was found to be 78.13%, 81.25% and 62.50%, respectively. False positivity was 6.66% with CS and 0% with other antigens. CF gave positivity with a pooled visceral gnathostomiasis serum and 3 of 10 (30%) of angiostrongyliasis sera. CS produced weakly positive ELISA with pooled opisthorchiasis and visceral gnathostomiasis sera. TS gave weak positive ELISA with a pooled opisthorchiasis serum. It was concluded that CF was the best antigen for use in ELISA for serodiagnosis of human neurocysticercosis.

The present status of trichinellosis in Thailand.

The epidemiology of trichinellosis in northern Thailand may be unique. Since 1962, outbreaks of the disease have occurred almost every year. The Department of Communicable Disease Control, Ministry of Public Health reported 118 discrete outbreaks of the disease, involving 5,400 patients, 95 of whom have died. Epidemiological investigations reveal that the outbreaks have occurred mostly in rural areas, associated with villagers celebrating local and traditional festivals such as the northern Thai New Year, wedding ceremonies, or other festive occasions. In almost all cases the source of infection has been traced to either hilltribe pigs, which are raised like wild animals, or to meat from wild boar. Infection is usually acquired through consumption of a local dish called "lahb," traditionally served during these festivities. This popular dish consists of raw finely chopped meat mixed with spices and chilies and is served nearly raw. Common clinical symptoms of trichinellosis in northern Thailand are fever and myalgia, presenting about two weeks after ingestion of raw meat containing encysted Trichinella larvae. Based on its infectivity for rats and pigs and on alloenzyme typing, the species appears to be Trichinella spiralis. The transmission cycle of trichinellosis in northern Thailand is primarily of a sylvatic type. Hilltribe pigs, wild boars, black bear and jackal are common reservoirs. Man intrudes into the cycle by eating the raw or under-cooked meat of these animals.

Bancroftian filariasis in Tambol Na-Sai, Amphoe Li, Lamphun Province: a preliminary survey for microfilaraemia.

A preliminary survey for Bancroftian filariasis in villagers of Ban Prabat Heuy Tom, Tambol Na-Sai, Amphoe Li, Lamphun Province was performed between July 12, 1986 and March 19, 1987. A total of 1,435 villagers comprising 668 females and 767 males were examined for microfilaraemia in peripheral blood. Microfilariae were found in five males of which two cases were found to have developed hydrocele at a lesser degree and all of them had formerly resided in an endemic area of Tak Province. Microfilarial periodicity was studied in two cases, and it was shown to be nocturnally subperiodic.

Studies on the Japanese encephalitis vectors in Amphoe Muang, Chiang Mai, Northern Thailand.

From February 1987 to January 1988, biological and ecological studies were made to obtain the basic knowledge of Japanese encephalitis vectors, Culex tritaeniorhynchus, Cx. gelidus, and Cx. fuscocephala, in Amphoe Muang, Chiang Mai, northern Thailand. The following results were found. Peaks in the population densities of the vectors as measured four times a month, by UV-light trap and human-baited trap collections, occurred during rainy season. The JE vectors in rural areas showed a sharp rise in the population in July when most of the rice fields were ploughed and a marked decline in mosquito population densities occurred after transplanting in August when the fields were flooded. The average number of larvae plus pupae per m2 in rice fields was highest in July when the fields were ploughed, but in the period from transplanting to harvesting (August to November), the densities were very low. Daily survival rates of the adult females, as estimated from parous rates, were mostly as high as 0.7 throughout the year.

Serodiagnosis of human gnathostomiasis.

An enzyme-linked immunosorbent assay (ELISA) was evaluated for serodiagnosis of human ocular and visceral gnathostomiasis in comparison to an indirect haemagglutination (IHA) and precipitin (PPT) tests. The ELISA antibody titers were found to range from 1:400 to 1:51,200 against somatic and 1:200 to 1:25,600 against excretory-secretory (ES) antigens. When sera were tested at single dilutions, the ELISA was positive in 7 of 8 gnathostomiasis cases while only 5 and 3 were positive by IHA and PPT respectively. The overall specificity of the ELISA was 96.7% and 97.4% with somatic and ES antigens respectively. Since somatic and ES antigens produced similar ELISA results, either can be used for diagnostic purpose. It was suggested that the ELISA was a reliable serodiagnostic test for human gnathostomiasis.

Filariasis in Tak Province, northwest Thailand: the presence of subperiodic variant Wuchereria bancrofti.

The microfilariae found in carriers at Tak Province, Northwestern Thailand were morphologically and morphometrically studied. It was found that the parasites conformed to that of W. bancrofti microfilaria. The microfilarial periodicity as determined from four carriers was found to be nocturnally (early evening) subperiodic type showing a distinct peak at 1800 hours.

Acute human isosporiasis in Thailand: a case report.

A case of acute human isosporiasis in Thailand was reported. A 57-year-old man developed diarrhoea after prednisolone administration for the management of nephrotic syndrome. Stool examination revealed numerous Isospora oocysts. On the basis of parasite morphology and sporulation time, it was identified as Isospora belli Wenyon, 1923. The patient recovered for the diarrhoea without specific treatment.

Scanning electron microscopic study of nocturnally subperiodic Brugia malayi (Filarioidea: Onchocercidae), Narathiwat, Southern Thailand.

Scanning Electron Microscopic (SEM) observations were made on the adult females and males of nocturnally subperiodic Brugia malayi (Narathiwat, Southern Thailand) from 8-month-old intra-peritoneally infected jirds (Meriones unguiculatus). Descriptions of the morphological surfaces of anterior end, vulva, body cuticle, anus, posterior end of females and anterior end, body cuticle, cloaca, caudal papillae, spicules, sheath, posterior end of males were demonstrated. The comparison among these and other filarial parasites were also investigated.

Evaluation of counterimmunoelectrophoresis for serodiagnosis of human cysticercosis.

Counterimmunoelectrophoresis (CIEP) was evaluated in comparison to the indirect haemagglutination test (IHA) for serodiagnosis of human cysticercosis. It was found that CIEP detected antibodies in 7 of 11 (64%) and IHA detected them in 6 of 11 (55%) confirmed cysticercosis sera. Only 2 of 130 control sera were positive by each technique. Taenia saginata adult worm extract was found to be satisfactory for use in CIEP in place of Taenia solium cysticercus extract, with only little loss of sensitivity. Finally, CIEP in combination with IHA greatly increased the diagnostic sensitivity for human cysticercosis.

Seroepidemiology of malaria in northern Thailand: II. Focal and temporal variations in endemicity.

Four population groups from regions of Northern Thailand were surveyed for the presence of antibodies to Plasmodium falciparum using the indirect immunofluorescent antibody (IFA) test. Each of the four populations was selected from areas known to represent different patterns of malaria transmission. Group 1 was from an area where there had been no malaria transmission for approximately 30 years. Individuals in this group below age 40 showed an extremely low prevalence of malaria antibodies. Group 2 was chosen from an area where low levels of transmission have continued despite more than 30 years of DDT spraying. In this group the age related pattern of malaria antibodies varied from village to village but in all villages there was a sharp increase in the prevalence of IFA positive tests in individuals over 30. The third group has had continuously high levels of transmission. Although there are differences in the age related prevalence of IFA positives when individual villages are compared, there is a greater prevalence at all ages than in the first two groups. The fourth group was selected from an area where transmission had recently resumed after freedom from indigenous cases for approximately six years. There was little difference in the prevalence of IFA positive individuals below the age of 25 but above that there was a steady increase in prevalence with age. The correlation of IFA antibody positives with known patterns of malaria transmission in these four areas demonstrates the usefulness of this serological technique in assessing malaria endemicity and the effectiveness of control measures as well as in the interpretation of other malaria statistics.

Scrub typhus and chiggers in northern Thailand.

It was reconfirmed that L. deliense was the most dominant chigger during the rainy season in northern Thailand. Overall prevalence of IgG antibody against R. tsutsugamushi among the rural villagers in the northern most part of Thailand was nearly 60% at the level over 1 : 10 by an indirect immunofluorescent test. The level of IgG and IgM antibody titers was considerably high as greater than or equal to 1 : 2560 in some sera, but did not markedly vary by age groups or sexes. Based on detection of IgM antibody, the probability of new or reinfections were considered.