School-based health education for the control of soil-transmitted helminthiases in Kanchanaburi province, Thailand.

Soil-transmitted helminthiases are major parasitic diseases that cause health problems world-wide. School-based health education is one of several basic interventions currently recommended by the World Health Organization for the control of these infections. A 3-year programme of health education for the control of soil-transmitted helminths (STH) has recently been completed in four primary schools in the Hauykayeng subdistrict of Thong Pha Phum district, in the Kanchanaburi province of Thailand. Overall, the percentage of the schoolchildren found infected with STH increased between the start of year 1 of the intervention (16.6%) and the end of year 2 (23.8%) but showed signs of falling by the end of year 3 (19.4%). Although none of these year-on-year changes in overall prevalence was statistically significant, some significant trends were detected when the six school grades (i.e. age-groups) were considered separately. The grade showing the highest prevalence of STH infection changed, from grade 6 (representing the oldest children investigated) at the start of year 1 (when grade-1 children were excluded from the survey) to grade 1 (representing the youngest children) at the ends of year 2 and year 3. By the end of year 3, the children in grades 5 and 6 had significantly lower prevalences of infection than the grade-1 subjects. The prevalence of STH infection in the grade-1 children was significantly higher than that in any of the older grades at the end of year 2 and significantly higher than that in grades 3-6 at the end of year 3. These results indicate that the health education had a greater impact on the children in the higher grades (who, presumably had better levels of understanding and practised better, personal, infection prevention) than on the younger children. Although school-based interventions can serve as a useful entry point for parasite control, more effort, including anthelminthic treatment, may be required among the youngest children. The activities need to be sustainable and supported by appropriate school-health policies.

Social and behavioral factors associated with Clonorchis infection in one commune located in the Red River Delta of Vietnam.

Social behavioral factors associated with Clonorchis infection are needed for control measures. The population in Nga Tan commune were randomly sampled and questioned to determine knowledge, perception, and health behavioral factors associated with Clonorchis infection among heads of households. The cellophane thick smear method was applied to examine their stool samples. Seven hundred and seventy-one cases were examined, the positive rates were 17.2%, 66.9%, 78.7%, 15.9%, and 0.14% for Clonorchis sinensis, Ascaris lumbricoides, Trichuris trichiura, hookworm, and Dicrocoelium dendriticum respectively. There was no significant difference between the infection rate of clonorchiasis, education level, and family income groups (p > 0.05). But there was significance difference between the infection rate of clonorchiasis and people living in different family sizes (p < 0.01). Thirty-four clonorchiasis patients treated with praziquantel 25 mg/kg/day for three days showed a cure rate in 30 days of 97.1%.

Sensitive and specific enzyme-linked immunosorbent assay for the diagnosis of Wuchereria bancrofti infection in urine samples.

We developed an enzyme-linked immunosorbent assay (ELISA) that detects filaria-specific immunoglobulin G4 antibodies in unconcentrated urine. The ELISA was positive in 87 of 91 (95.6%) urine samples collected from people with Wuchereria bancrofti microfilariae, antigen, or both. Of 298 urine samples collected in Thailand, Lao People's Democratic Republic, and Japan, where no human filariasis is known, 295 (99.0%) were negative by ELISA. Various intestinal nematode and fluke infections did not interfere with the ELISA. Urine samples with sodium azide could be kept at 37 degrees C for 4 weeks, and the time of urine collection did not influence ELISA results. This ELISA can be used to identify endemic foci of filariasis.

Parasitic contaminants in food.

There is a wide variety of food products that may be contaminated with one or more parasites and consequently enabling transmission to human beings. The prevalence of specific parasites in food supplies varies between countries and regions. Sources of food-borne products contaminated with parasites are pigs, cattle, fish, crabs, crayfish, snails, frogs, snakes and aquatic plants. One of the major factors influencing the prevalence of parasitic infections in the population is the habit, and traditional popularity of eating raw or inadequately cooked foods. The parasites that may be acquired by eating these foods are nematodes, trematodes, cestodes and protozoa. The major genera of parasites are Trichinella, Gnathostoma, Angiostrongylus, Anisakis, Paragonimus, Clonorchis, Opisthorchis, Fasciola, Fasciolopsis, Echinostoma, Taenia, Spirometra and Toxoplasma. These food-borne parasitic infections are public health problems worldwide. The contamination of food affects many including humans, livestock industry, agriculture, and food manufacturing and processing. Unsafe foods must be condemned and destroyed. Today there is increasing travel hence there is the risk of humans' acquiring food-borne parasitic infections through eating native food often raw. Moreover, the consumption of imported livestock and foods, especially from endemic areas of food-borne parasitic zoonoses, can be the cause of infection. Awareness should be heightened wherever and whenever raw or inadequately cooked food are consumed.

Strongyloides stercoralis infection and chronological changes of other soil-transmitted helminthiases in an endemic area of southern Thailand.

A field survey was conducted in 4 primary schools in Nakhon Si Thammarat Province, southern Thailand. By Sasa modified Harada-Mori cultivation method, 1.8% of the schoolchildren were found to be infected with Strongyloides stercoralis, and 25.1% had hookworm infection. By Kato's thick smear method, the overall prevalence of soil-transmitted helminths was 46.8%, being Trichuris trichiura 28.5%, hookworm 18.0%, and Ascaris lumbricoides 5.7%. Fecal examination, performed by Kato's thick smear and culture method, indicated that the prevalence of hookworm infection was 26.9%. The prevalence in the present study was very much lower than many previous reports in the past decade. This may indicate the partial success of the parasite control project in Thailand by mass treatment, improving the sanitation and personal hygiene of the people in the endemic area. In light infection with Trichuris, albendazole administered at a dosage of 200 mg daily for 3 days showed a 48.7% cure rate. When mebendazole was given at 100 mg twice daily for 3 days, its effectiveness was 88.5%. A lower cure rate was obtained (70.0%) in moderate to heavy infection.

Neurocysticercosis: utilizing the cystic fluid antigen from Taenia solium metacestodes for diagnosis by IgG-ELISA.

Cystic fluid, which has antigenic properties of whole Taenia solium cysticerci, was used to discriminate neurocysticercosis cases and other parasitic infections, especially helminthiases. Twenty-one neurocysticercosis and several kinds of 22 different parasitic infections, including HIV cases (n=234) evaluated a 90.48% sensitivity and 86.32% specificity of indirect ELISA as follows: a low antigen concentration of 5 microg/ml. serum dilution of 1:400, conjugate dilution of 1:2,000 and a cut-off value of 0.349. Eight different helminthic infections (n = 25); echinococcosis (8/10), gnathostomiasis (6/8), strongyloidiasis (5/14), hookworm infection (1/18), angiostrongyliasis (2/25), opisthorchiasis (1/18), onchocercosis (1/3) and toxocariasis (1/6) were cross-reactive with this antigen. No serum antibody from other brain infections in the study gave a reaction with the antigen. In this study, the cystic fluid antigen gave high sensitivity of the test. However, the antigen contains various antigenic molecules able to bind with antibodies from several of the above helminthic sera, especially echinococcosis and gnathostomiasis. In Thailand, gnathostomiasis is one of the more famous tropical diseases but echinococcosis is quite rare. Cystic fluid antigen should be further investigated for its specific finding in diagnosis.

Gnathostome infection in swamp eels, Fluta alba, in central Thailand.

To investigate the distribution of gnathostome worms in central Thailand, the infective larvae of Gnathostoma spp were examined from the flesh and liver of swamp eels, Fluta alba. Seven hundred and eighty-eight eels were purchased from markets in 11 provinces; Ang Thong (30), Ayutthaya (36), Chachoengsao (30), Lop Buri (30), Nakhon Nayok (437), Pathum Thani (30), Prachin Buri (48), Ratchaburi (53), Saraburi (30), Samut Prakan (30) and Suphan Buri (34). The highest rate of gnathostome infection was observed in swamp eels from Nakhon Nayok (68.7%). The infection rates in Ayutthaya, Ang Thong, Prachin Buri, Ratchaburi, Saraburi and Lop Buri were 33.3%, 26.7%, 25.0%, 18.9%, 13.3% and 10.0% respectively. Gnathostome larvae were not found in swamp eels from Chachoengsao, Pathum Thani, Samut Prakan and Suphan Buri. Among the 9,573 larvae recovered, almost all were the advanced third stage larvae of G. spinigerum, except one larva from Nakhon Nayok and two larvae from Ratchaburi which were identified as the advanced third stage larvae of G. vietnamicum and G. hispidum respectively. This study is the first report of swamp eels as natural intermediate hosts of G. vietnamicum and G. hispidum.

Toxocara and Gnathostoma among stray canines in Bangkok.

Stomachs and intestines of 88 adult and 112 young stray dogs were obtained from the Rabies Control Subdivision, Bangkok, and examined especially for the presence of Gnathostoma spinigerum and Toxocara canis. Forty-five dogs were found positive for T. canis (overall prevalence 22.5%) but none were found infected with G. spinigerum. The prevalence of T. canis in young dogs was 37.5% (42 of 112) whereas in adult dogs was only 3.4% (3 of 88). The total number of T. canis recovered from the 45 positive dogs was 272 (averaging 6.0 worms/dog). This includes 268 worms from 42 young dogs (averaging 6.4 worms/dog) and four worms from three adult dogs (averaging 1.3 worms/dog). The average number of worms, according to sex and stage, per young dog were as follows: male worms 2.4 +/- 3.5 (range 0-15), female worms 2.8 +/- 3.5 (0-16), immature worms 1.2 +/- 2.5 (0-9), and all worms 6.4 +/- 8.2 (1-34). The maximum number of worms per young dog was 34 while the minimum was one, and 35.7% (15/42) of these young dogs harbored only one worm. The body length of the recovered T. canis were as follows: males measuring 3.0-12.0 cm (averaging 7.1 +/- 2.1 cm), females 4.1-18.2 cm (11.0 +/- 4.1 cm), and immature worms 0.7-3.7 cm (2.1 +/- 0.8 cm).

Evaluation of Bithynia funiculata snail antigens by ELISA-serodiagnosis of human opisthorchiasis.

Four batches of crude somatic antigens from: (1) Opisthorchis viverrini adult worms, (2) Bithynia funiculata-whole body, (3) B. funiculata-head-foot, and (4) B. funiculata-visceral mass were assayed against sera from 81 opisthorchiasis patients, 30 parasite-free healthy individuals, and 50 individuals infected with other helminthic infections, and their antibody levels determined. By IgG-ELISA, the antigenic reactive proteins were found in both the head-foot and the visceral mass of B. funiculata snails, but the whole snail antigens gave the best results. Furthermore, it was as good as when O. viverini antigens were used. Antibody levels of sera from patients with opisthorchiasis assayed against antigens from whole B. funiculata snails were significantly higher than those of the other two groups. The cut-off value for positivity at 0.228 gave 80.2% sensitivity and 81.2% specificity. Cross reactions were observed with sera from patients with paragonimiasis and strongyloidiasis. No cross reactions were found to occur with sera from healthy individuals.

Effect of ivermectin on experimental gnathostomiasis in rabbits.

The efficacy of ivermectin against advanced third stage larvae of Gnathostoma spinigerum was investigated in rabbits. Six experimentally infected rabbits were treated at a single dose, 0.2 mg/kg of ivermectin subcutaneously, four weeks after infection. Another two rabbits were treated, once and three times, with 2 mg/kg at varying numbers of days after infection. Five rabbits served as untreated controls. All rabbits were sacrificed about the 28th week after infection. The reductions of worm load in the treated groups were 74.2% and 84.2% respectively. The immune response, detected by ELISA, was similar in treated and control rabbits.

Practicable IFAT slide antigen preparations for detection of Gnathostoma spinigerum antibodies in rabbits.

This study was designed to determine which stage of Gnathostoma spinigerum and which method of the preparation of test antigens are the most suitable for the detection of antibodies in serum of rabbits infected with advanced third stage larvae (AL3) of G. spinigerum by the indirect fluorescent antibody test (IFAT). Antigens from parasite ova and first stage larvae (L1) were obtained from freshly preserved specimens and affixed to glass slides with egg albumin. AL3 antigens consisted of paraffin sections, cryostat sections and pellets of crude worm soluble extract. Slides of adult male and female worms were prepared in cryostat sections. Pellets of crude worm soluble extract (AL3) smeared onto slides gave the best positive reaction followed by AL3 cryostat sections and L1.

Demonstration of species-specific antigens of Gnathostoma spinigerum, a preliminary attempt.

An attempt was made to demonstrate the presence of species-specific antigens for Gnathostoma spinigerum advanced third-stage larvae (GsAL3) in a rabbit receiving weekly immunization with GsAL3 for seven weeks. The homologous and heterologous antibodies against GsAL3 and G. doloresi adult worm (Gd) antigens were initially detected by immunoelectrophoresis (IEP) and ELISA after the second immunization, and their levels were gradually increased with the number of immunizations. Though cross-reactivity between GsAL3 and Gd were shown with both tests, species-specific antibodies for the homologous antigens were demonstrated. After cross-absorption of rabbit hyperimmune serum was collected after the seventh immunization, seven 'putative' species-specific precipitin bands of GsAL3 were identified. The ELISA values of the rabbit hyperimmune serum showed 50% inhibition after absorption with 0.7 micrograms/ml of homologous GsAL3 antigens as opposed to 1.0 micrograms/ml of the heterologous Gd antigens.

ELISA for diagnosis of gnathostomiasis using antigens from Gnathostoma doloresi and G. spinigerum.

ELISA was developed for the detection of IgG antibody in sera obtained from patients in Japan and in a foreign country. Gnathostoma doloresi adult antigen was less specific than G. spinigerum advanced third-stage larval antigen but their sensitivity were similar. Cross reactivity was observed in Toxocara canis-, Anisakis-, Paragonimus westermani- and Fasciola-infected sera when G. doloresi adult worms but not G. spinigerum advanced third-stage larvae were used as antigens.