Prevalence of intestinal parasitic infections in northern Vietnam.

We surveyed the prevalence of parasitic infections in the mountainous province of Hoa Binh, north-west Vietnam, involving 526 households of six ethnic groups: Muong, Kinh, Dao, Thai, Tay and Hmong. Eggs or cysts of at least one parasite species were detected in 88% of stool samples (n = 2522). Prevalences of nematodes were high among all ethnic groups: hookworm (52%), Trichuris trichiura (50%) and Ascaris lumbricoides (45%). Ascaris infection appeared to be lower in households owning a latrine, was highest among children and decreased with age. Prevalence of hookworm rose during childhood, remained high until old age, was highest among adult women, but was not linked to anaemia. Eggs of Chlonorchis spp. were found in 126 (5%) individuals (of the Muong, Kinh or Thai groups only). Chlonorchiasis increased with age and was highest among adult men. Taenia eggs were found in three individuals (0.1%). Giardia lamblia was found in all districts and among all groups and the prevalence of infection was estimated at 3%.

Efficacy of artesunate and praziquantel in Schistosoma haematobium infected schoolchildren.

Praziquantel is the current mainstay for morbidity control of schistosomiasis. Artemisinin and its derivatives, widely used for the treatment of malaria, also display antischistosomal properties. The present study is an effort to assess the therapeutic efficacy of artesunate, an artemisinin derivative, in Schistosoma haematobium infections in a human population. The efficacy of artesunate and praziquantel were comparatively studied in primary schoolchildren from two villages, Lampsar (n=180) and Makhana (n=108), located along the Lampsar river in the delta of the Senegal River Basin in Northern Senegal (West Africa). In each village, half of the infected children were treated with a single oral dose of 40 mg/kg praziquantel and half with artesunate following the recommended malaria monotherapy regimen. For both drugs, cure and egg count reduction rates were, without apparent explanation, higher in Makhana than in Lampsar. In both villages, high and nearly comparable egg count reduction rates were obtained with both drugs at each follow-up after treatment (5, 12 and 24 weeks) in the heavy infected group of children (>50 eggs/10 ml of urine). No major adverse effects were observed. The results demonstrate that artesunate is effective against S. haematobium, but the results obtained with praziquantel were consistently better.

The unreliability of the Kato-Katz technique limits its usefulness for evaluating S. mansoni infections.

The Kato-Katz technique, a (semi) quantitative stool examination technique, is generally recommended for diagnosis and evaluation of Schistosoma mansoni infection by schistosome experts. However, egg counts are subject to important variability. In order to quantify the reproducibility of egg counts using the Kato-Katz technique, field data of 1255 observations on 299 subjects infected with Schistosoma mansoni were analysed. Agreement between repeated observations was assessed both categorically (kappa statistic) and continuously (analysis of variance). The day-to-day variation of egg counts was much greater than the variation due to different observers or different slides. The quantitative reproducibility was low: the weighted kappa statistic was 0.39 between specimens of different days, 0.62 between slides of the same specimen and 0.81 between observers of the same slide. Therefore the classification of individual patients into groups based on egg counts, used as a measure of morbidity, must be interpreted with great care, especially in longitudinal studies. Usefulness of the Kato-Katz technique appears limited. Its reproducibility is low. It cannot be recommended as a routine test in a primary health care setting or in a hospital laboratory because safety and detection of other parasites are better assured by other techniques. It can be used in epidemiological studies and evaluation of schistosomiasis control programmes, but here too, other techniques might be preferred.

What is the effect of combining artesunate and praziquantel in the treatment of Schistosoma mansoni infections?

A group of 110 individuals with Schistosoma mansoni infection was investigated. Patients were allocated to one of three treatment groups and given artesunate or praziquantel alone or both in combination. Combined artesunate-praziquantel significantly increased the number of individuals cured at 5 weeks post-treatment, but at 12 weeks was only better than artesunate alone and at 24 weeks there was no statistically significant difference between the three groups. Egg count reduction rate was similar to the rate obtained with praziquantel used alone.

Glucose-6-phosphate dehydrogenase deficiency in northern Vietnam.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency was evaluated in 1676 schoolboys in northern Vietnam. The trait was nearly absent in boys of the Kinh (0.5%) and the Mong (0.7%) ethnic groups that traditionally have lived outside malaria transmission areas. Prevalences among ethnic groups living in the foothills, the breeding area of the main malaria vector Anopheles minimus, ranged from 9.7% to 31%. These findings support the hypothesis of a selective advantage of the trait in Plasmodium falciparum-endemic areas.

Identification of two species within the Anopheles minimus complex in northern Vietnam and their behavioural divergences.

Elucidating the complex taxonomic status of the major malaria vector taxa and characterising the individual species within each complex is important for understanding the complexity of the vector system in the south-east Asian region and will allow to estimate the impact of vector control measures. This applies to countries such as Laos, Cambodia and Vietnam that spend about 60% of their malaria control budget on implementing vector control activities. We used isozyme electrophoresis to clarify the Anopheles minimus s.l. species composition in northern Vietnam and identify behavioural divergences of individual species. Using different collection methods, adult mosquitoes were caught at monthly intervals from June to November 1995 in four villages. An. minimus s.l. could be distinguished from closely related species, An. aconitus and An. jeyporiensis, at the Octanol dehydrogenase (Odh) enzyme locus. Significant positive Fis values gave clear evidence of nonrandom mating within the An. minimus s.l. population. The highest heterozygote deficiency was observed at locus Odh, which was diagnostic for 2 sympatric An. minimus species in Vietnam similar to the An. minimus A and C species known from Thailand. We found no evidence for restricted gene flow between monthly samples, villages, or collection methods in either of the two An. minimus species. They occurred in sympatry, but in different proportions depending on the collection site, and had dissimilar resting and biting behaviours. Thus a vector control strategy will have a nonuniform effect on the various components of this diverse vector system.

Control of malaria vectors: cost analysis in a province of northern Vietnam.

The cost of permethrin-treated bednets (50% EC; 0.2 g/m2, 2 rounds per year) was compared to the cost of residual spraying with lambdacyhalothrin 10% WP (0.03 g/m2, once yearly) in Hoa Binh, a mountainous province in northern Vietnam. Calculations of the amounts of insecticides needed were based on national guidelines, on data from a cross-sectional survey and on district activity reports. The actual cost of insecticide required per person per year was lower for impregnation (US$ 0.26) than for spraying (US$ 0.36), but the difference was smaller than expected. The total cost for impregnated bednets per person per year amounted to US$ 0.90 compared to USS 0.47 for spraying. The determining factor was the cost of the net, amounting to US$ 0.58 per person per year, assuming a 5-year life of the net. Other material (excluding nets), labour and transport combined, accounted for only 17% of the impregnation cost and 23% of spraying expenses. However, for the National Malaria Control Programme of Vietnam, the cost per person per year for impregnated bednets amounted to US$ 0.32 only, because the vast majority of nets are bought by the population. For spraying, the programme had to bear the entire cost.

A simple field test for detecting pyrethroids on impregnated nets.

We tested a modified Beilstein method for detecting pyrethroids on bednets under laboratory conditions using an emulsifiable concentrate of permethrin (50 EC) for viability as a simple standardized field test and to judge its reliability for detecting different insecticide doses. At the recommended doses of permethrin (0.5 g/m2), sensitivity was near 100%, even when small pieces of fabric were tested and time of extraction was limited. In unwashed nets sensitivity stayed high (80-95%) down to 0.1 g active ingredient/m2. In untreated nets false positives were rare (0-2%). The test could become a valuable tool in vector control programmes: it is cheap, easy to learn and to perform. The Lot Quality Assurance Sampling method, using an upper and lower performance threshold, could be applied for monitoring the impregnation campaigns.

ParaSight-F test to diagnose malaria in hypo-endemic and epidemic prone regions of Vietnam.

The antigen capture ParaSight-F test was evaluated during a drug sensitivity survey in a hypoendemic region of northern Vietnam. When only asexual blood forms of P. falciparum were considered, sensitivity of ParaSight-F was 100%, specificity 88% (95% CI 95-80%), positive predictive value 68% (95% CI 85-50%) and negative predictive value 100%. ParaSight-F proved very convenient for rapid screening and selection of patients to enrol in a drug sensitivity study. In northern Vietnam, the introduction of the test as a routine diagnostic tool is not justified, considering its high cost, the necessity to carry out the treatment of presumptive Plasmodium vivax cases and the persistence of positive reactions following treatment. However, the test will be a valuable tool in remote areas in emergency situations, where rapid confirmation of a P. falciparum outbreak is required.

Clinical investigation of a population recently infected with Schistosoma mansoni (Richard-Toll, Senegal).

Following the introduction of large-scale irrigation, an exceptional epidemic of intestinal schistosomiasis occurred in northern Senegal when a non-immune population was exposed to massive infection. Subjects infected with Schistosoma mansoni were followed up parasitologically and clinically from the onset of the epidemic. After the initial evaluation, patients received a health education session and were treated with praziquantel in a dose of 30 mg/kg. One year after this treatment, S. mansoni eggs were found in the stools of 227/301 subjects (75%). Twenty-three per cent of subjects excreted > 400 eggs per gram (e.p.g.) and 11% excreted > 1000 e.p.g. of faeces. Overall, the geometric mean was 191 e.p.g. of faeces in infected individuals. The prevalence of diarrhoea was reduced from 55 to 29%, the prevalence of bloody diarrhoea from 44 to 11% and the prevalence of abdominal discomfort from 66 to 41%. No hepatomegaly was found in these patients either before or one year after treatment. Splenomegaly was reduced from 30% (measured by ultrasound) to 3% (on clinical examination). Morbidity associated with S. mansoni infection was considerably reduced one year after treatment with praziquantel (30 mg/kg).

Epidemic schistosomiasis in the delta of the Senegal River Basin, Senegal: responses of the health care system.

Since 1988, the delta of the Senegal River Basin has experienced an exceptional epidemic of intestinal schistosomiasis, following the development of large irrigation projects. Urinary schistosomiasis was also rapidly spreading. The response of the health care system to the epidemics is described. Control was integrated in the existing health care system, according to the general health policy of Senegal. Control was based on passive detection, treatment, health education and information. The availability of praziquantel was assured. Priority was given to the development of health services in general. Initial reports have also attracted different research groups to the area. The variety of epidemiological situations made this area unique for research. Researchers would like to observe untreated communities to study the development of immune mechanisms. Inevitably such approach must lead to confrontation with local health services which should offer ethically and medically correct management of infected individuals and affected communities.

Preliminary study of urinary schistosomiasis in a village in the delta of the Senegal river basin, Senegal.

Three years after the first cases of urinary schistosomiasis infection were reported in the village of Mbodiene, Senegal, Schistosoma haematobium eggs were found in 87% of the inhabitants of this village; 30% were heavily infected (> 50 eggs per 10 mL urine). The prevalence of infection was very high in all age groups, but children showed more intense infections. No difference between sexes was found. In the special situation of a very high prevalence, test strips for proteinuria and haematuria are not very useful for the individual diagnosis of S. haematobium infection. Six and 12 weeks after treatment with a single dose of praziquantel (40 mg/kg), S. haematobium eggs were found in 25% and 30% of the treated subjects, respectively. Bulinus globosus was identified as intermediate host, but other snail vectors may also play a role. S. mansoni eggs were found in 1% of the population. Both S. haematobium and S. mansoni are spreading in the delta of the Senegal river.

Morbidity due to heavy Schistosoma mansoni infections in a recently established focus in northern Senegal.

A study of morbidity due to Schistosoma mansoni infection was carried out in Ndombo, a recently established but intense focus in northern Senegal. A random population sample (n = 422) was examined by repeated egg counts, standardized interviews, and clinical examinations. Egg counts were positive in 91%, with more than 1,000 eggs per gram of feces in 41% of the subjects. Abdominal discomfort was reported by 60% of the subjects, diarrhea by 33%; 17% of the stools were liquid upon inspection. Hepatomegaly was mostly mild and found in 7% of the subjects, mainly in males less than 20 years of age. Splenomegaly was detected in only 0.5% of the people examined. There was no significant correlation between the frequency of complaints or symptoms and egg counts. The remarkably mild morbidity in spite of the intense level of many infections may be explained by the recent nature of the focus; more severe chronic morbidity may develop in the future.

Hepatosplenic alterations determined by ultrasonography in a population recently infected with Schistosoma mansoni in Richard-Toll, Senegal.

Three years after intestinal schistosomiasis had been reported for the first time in the delta of the Senegal River Basin, an ultrasonographic study was conducted on 358 subjects of the community of Richard-Toll with a proven Schistosoma mansoni infection and compared with the findings from 352 uninfected subjects of a nearby town. Periportal thickening was found in 119 subjects (33%) in only one of whom it was greater than 10 mm; liver parenchyma lesions were found in 40 subjects (11%), at about the same rate in all age groups. No correlation was found between hepatomegaly and schistosomiasis. Frequency of thickening of the omentum was significantly higher in Richard-Toll than in the control group. 11% of the Richard-Toll subjects had portal vein diameters significantly larger than the values in the control group; of those, 6% had no periportal fibrosis sign in the liver. Significantly more splenomegaly was found in the infected group, though malaria as an aetiological agent cannot be ruled out. Based on periportal alterations and parenchyma lesions only, 141 (39%) subjects in the Richard-Toll group had alterations, corresponding to the World Health Organization proposed criteria for stage I; one subject had alterations corresponding to stage II. As S. mansoni infection is still new in this area, the patho-anatomical pattern is likely to change significantly in the future.

Outbreak of intestinal schistosomiasis in the Senegal River Basin.

Intestinal schistosomiasis has never been reported in the delta of the Senegal River Basin. A year and a half after the Diama dam became operational, a first case of Schistosoma mansoni infection was detected at Richard-Toll. In 1988 and 1989, 1,935 stool examinations out of a sample of 3,926 were found positive for S. mansoni. The progression of positive stool samples is rapid in all neighbourhoods of Richard-Toll: 1.9% positive examinations in 1988 compared to 71.5% in the last quarter of 1989. One thousand nine hundred and sixty nine Biomphalaria pfeifferi were collected during several malacological surveys carried out from February 1989 to December 1989 at three observation points. An emission of S. mansoni furcocercariae was determined in 44 out of 926 B. pfeifferi (4.75%) examined during this same period. Intestinal schistosomiasis is new in this area and spreading quickly. Rapid intervention measures are required immediately.