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Biomedical subjects

D Engels

Publications and source records attributed to D Engels.

At least 19 recordsLinked to original sources
PubMed2005

Schistosomiasis control in China: the impact of a 10-year World Bank Loan Project (1992-2001).

China has been carrying out large-scale schistosomiasis control since the mid-1950s, but in the early 1990s, schistosomiasis was still endemic in eight provinces. A World Bank Loan Project enabled further significant progress to be made during the period 1992-2001. The control strategy was focused on the large-scale use of chemotherapy -- primarily to reinforce morbidity control -- while at the same time acting on transmission with the ultimate goal of interrupting it. Chemotherapy was complemented by health education, chemical control of snails and environmental modification where appropriate. A final evaluation in 2002 showed that infection rates in humans and livestock had decreased by 55% and 50%, respectively. The number of acute infections and of individuals with advanced disease had also significantly decreased. Although snail infection rates continued to fluctuate at a low level, the densities of infected snails had decreased by more than 75% in all endemic areas. The original objectives of the China World Bank Loan Project for schistosomiasis control had all been met. One province, Zhejiang, had already fulfilled the criteria for elimination of schistosomiasis by 1995. The project was therefore a success and has provided China with a sound basis for further control.

Animals↗
PubMed2005

The WHO dose pole for the administration of praziquantel is also accurate in non-African populations.

In 2001, WHO developed a pole for the administration of praziquantel without the use of weighing scales, with encouraging results in African populations. In the present study, the pole was tested on height/weight data from 9354 individuals from 11 non-African countries. In more than 98% of the individuals (95% CI 97.8-98.4) the pole estimated an acceptable dosage (30-60 mg/kg), a performance statistically similar to that observed in African populations. Reproducing the present pole in the form of a strip of paper and including it in each container of praziquantel would greatly facilitate the administration of the drug in large-scale interventions.

Adolescent↗
PubMed2004

Progress in the prevention and control of schistosomiasis and soil-transmitted helminthiasis.

In the last two decades important progress has been made in the understanding the epidemiology and the disease burden of schistosomiasis and soil-transmitted nematodes infection. In addition, practical tools for disease control have been developed and a strategy for the prevention and control of morbidy of schistosomaisis and soil-transmitted nematodes infection has been endorsed by the World Health Organization. This paper presents the recent progress in the prevention and control of these infections: the estimates of chronic and subtle morbidity in high risk groups and the evidence that these chronic and severe sequelae of infections can be reversed by appropriate treatment; the use of anthelminthic drugs during pregnancy and lactation; the relevance to control morbidity due to these infections also in pre-school children; the efficacy of anthelminthic drugs and the possible threat of drug resistance; price, quality and accessibility of treatment by delivering drugs through the school system and ways of reaching also non-enrolled school-age children. Finally, the strategy, targets and recommendations of the World Health Organization for the control of schistosomiasis and soil-transmitted nematodes infection are described.

Animals↗
PubMed2004

Schistosomiasis.

Explore the source record for details and available documents.

Animals↗
PubMed2002

The global epidemiological situation of schistosomiasis and new approaches to control and research.

While the distribution of schistosomiasis has changed over the last 50 years and there have been successful control programmes, the number of people estimated to be infected or at risk of infection has not been reduced. Today, 85% of the number of infected people are estimated to be on the African continent where few control efforts are made. In terms of disease burden, there is therefore a growing discrepancy between sub-Saharan Africa and the rest of the world. WHO has now developed a dual strategy for the control of schistosomiasis: a strategy for morbidity control adapted to the public health context in high burden areas, and a strategy to consolidate control in areas where a low endemic level has been reached and elimination may be feasible. Related to this new vision, some research needs are pointed out.

Africa↗
PubMed2002

Water-related disease patterns before and after the construction of the Diama dam in northern Senegal.

The ecological changes caused by projects for the development of water resources are known to affect the epidemiology of water-related diseases. The effects of the construction of the Diama dam (completed in 1986) in the Senegal River on the epidemiology of malaria, urinary and intestinal schistosomiasis, diarrhoea and dysentery were investigated in four districts in northern Senegal. To make allowance for any general trend in reported morbidity (caused by changes in demography or the healthcare system), the numbers of cases of these illnesses reported by the basic healthcare facilities before and after the completion of the dam were compared with those of respiratory disease. Prior to the construction of the dam, malaria was the most encountered water-related disease in the medical records of all districts, followed by diarrhoea, dysentery and urinary schistosomiasis. This order remained the same after the completion of the dam. Despite the optimism of health-assessment reports prepared prior to the construction of the Diama dam, the unexpected appearance and spread of intestinal schistosomiasis as well as an increase in the incidence of urinary schistosomiasis have aggravated public health in the Senegal River basin. It remains to be judged whether the economic benefits of the dam will counterbalance its adverse effects.

Diarrhea↗
PubMed2001

Are poor responses to praziquantel for the treatment of Schistosoma mansoni infections in Senegal due to resistance? An overview of the evidence.

This paper summarizes and concludes in-depth field investigations on suspected resistance of Schistosoma mansoni to praziquantel in northern Senegal. Praziquantel at 40 mg/kg usually cures 70-90% of S. mansoni infections. In an initial trial in an epidemic S. mansoni focus in northern Senegal, only 18% of the cases became parasitologically negative 12 weeks after treatment, although the reduction in mean egg counts was within normal ranges (86%). Among other hypotheses to explain the observed low cure rate in this focus, the possibility of drug resistance or tolerance had to be considered. Subsequent field trials with a shorter follow-up period (6-8 weeks) yielded cure rates of 31-36%. Increasing the dose to 2 x 30 mg/kg did not significantly improve cure rates, whereas treatment with oxamniquine at 20 mg/kg resulted in a normal cure rate of 79%. The efficacy of praziquantel in this focus could be related to age and pre-treatment intensity but not to other host factors, including immune profiles and water contact patterns. Treatment with praziquantel of individuals from the area residing temporarily in an urban region with no transmission, and re-treatment after 3 weeks of non-cured individuals within the area resulted in normal cure rates (78-88%). The application of an epidemiological model taking into account the relation between egg counts and actual worm numbers indicated that the low cure rates in this Senegalese focus could be explained by assuming a 90% worm reduction after treatment with praziquantel; in average endemic situations, such a drug efficacy would result in normal cure rates. Laboratory studies by others on the presence or absence of praziquantel resistance in Senegalese schistosome strains have so far been inconclusive. We conclude that there is no convincing evidence for praziquantel-resistant S. mansoni in Senegal, and that the low cure rates can be attributed to high initial worm loads and intense transmission in this area.

Animals↗
PubMed2000

The global status of schistosomiasis and its control.

Schistosomiasis is being successfully controlled in many countries but remains a major public health problem, with an estimated 200 million people infected, mostly in Africa. Few countries in this region have undertaken successful and sustainable control programmes. The construction of water schemes to meet the power and agricultural requirements for development have lead to increasing transmission, especially of Schistosoma mansoni. Increasing population and movement have contributed to increased transmission and introduction of schistosomiasis to new areas. Most endemic countries are among the least developed whose health systems face difficulties to provide basic care at the primary health level. Constraints to control include, the lack of political commitment and infrastructure for public health interventions. Another constraint is that available anti-schistosomal drugs are expensive and the cost of individual treatment is a high proportion of the per capita drug budgets. There is need for increased support for schistosomiasis control in the most severely affected countries.

Africa↗
PubMed2000

A comparative analysis of the cost-effectiveness of treatment based on parasitological and symptomatic screening for Schistosoma mansoni in Burundi.

OBJECTIVES: To assess the cost-effectiveness of three alternative screening strategies in delivering treatment to patients presenting with symptoms suggestive of S. mansoni, using data collected from 17 PHCCs in the Rusizi Plain, Burundi. The three strategies were: (1) screening all symptomatic patients using a Kato-Katz smear and treating only the ones found positive; (2) treating all symptomatic patients or (3) treating only those presenting with symptoms of severe diarrhoea (blood in stool). METHODS: The database consisted of 41 051 visits of symptomatic patients to the 17 PHCCs during 1990. Effectiveness was measured as the number of infected patients treated (gold standard: 25-mg Kato-Katz smear). Cost-effectiveness ratios (CERs) (cost in US$ per infected patient treated) were used to compare the control strategies. Sensitivity analysis was performed to assess the effect of drug price and prevalence of infection on the CERs. RESULTS: The overall prevalence of S. mansoni infection was 9.5% (95% CI = 9.1%, 9.9%). Treating only those with severe symptoms of infection would have left 92% of infected patients untreated. Performing a Kato-Katz smear to confirm the diagnosis was more cost-effective than treating all symptomatic patients on a presumptive basis, with CERs of 4.2 US$ and 12.43 US$ per infected person treated, respectively. Sensitivity analysis showed that, for a cost of 0.99 US$ per dose of praziquantel, the Kato-Katz option remained the most cost-effective approach for prevalences under 76%. For a drug price of 0.21 US$ per dose, both strategies would have become equivalent. The latter value varied extensively per PHCC (range 0.17 US$ to 0.51 US$), due to the different prevalences of infection (range 0.5% to 34.3%). CONCLUSION: We found that using severe diarrhoea as an indicator for infection was not appropriate, and that screening symptomatic patients with the Kato-Katz method remained the most cost-effective approach in the given setting. The CER of treating all symptomatic patients on a presumptive basis depended very much on the drug price and the endemic level.

Adolescent↗
PubMed2000

Specificity of circulating antigen detection for schistosomiasis mansoni in Senegal and Burundi.

The specificity of schistosome circulating antigen detection was determined in negative individuals from two S. mansoni- endemic countries, Senegal and Burundi, and compared with results from Dutch control individuals. A nearly absolute specificity was achieved for circulating anodic antigen (CAA) detection in serum, irrespective of the target population or sample pretreatment method. Circulating cathodic antigen (CCA) detection in serum and urine resulted in a lower specificity than serum CAA detection. Apparent large differences in specificity of CCA detection between countries were mainly due to pretreatment methods. Apparently, the alkaline/heating pretreatment method is not as effective as trichloroacetic acid (TCA)-pretreatment in removing (certain) interfering components, which may vary between populations. In view of the development of the urine CCA assay into a noninvasive screening test, a slightly lower specificity may still be acceptable. For precise epidemiological analyses the highly specific serum CAA assay remains the method of choice.

Adolescent↗
PubMed2000

[Reduced morbidity of schistosomiasis: report from an expert workshop on the control of schistosomiasis held at CERMES (15-18 February 2000, Niamey, Niger)].

Schistosomiasis remains a problem for public health in sub-Saharan Africa. Despite past efforts, cases have not decreased significantly. Schistosoma haematobium and S. mansoni are endemic in all the West African countries. The distribution of both parasites is focal. During a workshop held at CERMES in Niamey, in February 2000, a group of experts recommended that schistosomiasis control be considered as a public health priority in all the endemic West African countries, and National Control Programmes rapidly implemented. The objective of these control programmes would be to reduce schistosomiasis-related morbidity. Case detection should be based on clinical symptoms such as haematuria or bloody diarrhoea, and be carried out at two levels: health care centres and schools, in order to reach patients and school-age children. Health workers should be trained in case detection and community based control of schistosomiasis. The assembled experts advocated the use of praziquantel dosed at 40 mg.kg-1, which therefore must be made available and accessible in outlying areas. Associated measures consist of sanitation, water supply and health education, especially aimed at improving patients' treatment-seeking behaviour. A West African network for schistosomiasis control was created during the workshop. It runs on the Web site of CERMES as network co-ordinator. (http://www.mpl.ird.fr/cermes/).

Africa South of the Sahara↗
PubMed1998

Day-to-day fluctuation of schistosome circulating antigen levels in serum and urine of humans infected with Schistosoma mansoni in Burundi.

Day-to-day fluctuations of both circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) in serum and urine were examined simultaneously in a group of Schistosoma mansoni-infected individuals from Burundi and compared with each other and with fecal egg count fluctuations. Significant correlations were found between fecal egg counts and circulating antigens (CAA and CCA) and between circulating antigen levels in serum and urine samples. The cumulative percentage of positive results after three samplings was highest for urine CCA detection, followed by fecal egg counts, serum CCA, serum CAA, and urine CAA detection, respectively. It was demonstrated that circulating antigen levels in both serum and urine showed less fluctuation than fecal egg counts, except for urine CAA levels. The serum CAA detection assay in particular, although less sensitive in this low endemic area in Burundi, gave very constant measurements over a period of one week. Our results indicate that detection of circulating antigens in a single serum or urine sample provides a quantitatively more stable diagnosis of S. mansoni infection than fecal egg counts based on a single stool examination.

Adolescent↗
PubMed1997

Validation of a chart to estimate true Schistosoma mansoni prevalences from simple egg counts.

Schistosoma mansoni egg counts by faecal examination vary considerably and are not very sensitive, so prevalences are underestimated. The distribution of egg counts can adequately be described by a stochastic model which distinguishes variation in counts between persons and variation in repeated counts within a person. Based on this model a pocket chart has been developed which predicts the proportion of individuals harbouring at least 1 S. mansoni worm pair-the 'true prevalence'-from a simple single survey prevalence and geometric mean egg count (using common duplicate 25 mg Kato-Katz smears). The current paper describes the validation of this chart by comparing predicted true prevalences with prevalences observed after 5-7 repeated Kato-Katz faecal examinations (Burundi), by examination of a large quantity of stool using the Visser filter (Brazil) or a selective sedimentation-filtration method (Surinam). Because 5-7 repeated examinations do not suffice to measure all infections, predictions have been made of the cumulative proportion positives over 5-7 surveys-the 'approximate true prevalence'-as well. After dividing the data into age groups, 12 different subsets were considered for validation. In all 12 cases, predicted true prevalences (or approximate true prevalences for the Burundi data) agree well with those observed. The overall agreement depends only slightly on the assumed relationship between worm numbers and mean egg counts, with a good fit for a productivity between 0.8 and 4.4 eggs per gramme faeces (EPG) per worm pair (WP). This interval includes the most plausible value from the literature, i.e. 1.0 EPG/WP, which has been applied in the initial pocket chart. These findings support the validity of the chart to predict true prevalences for a wide range of productivity assumptions, and reinforces the applicability of its underlying stochastic model to describe egg count variation. However, as predictions appear to vary importantly when using only part of the data, it is also concluded that the pocket chart never compensates for limited validity of initial single survey prevalences and geometric means in consequence of small sample sizes.

Adolescent↗
PubMed1997

Variation in weight of stool samples prepared by the Kato-Katz method and its implications.

We investigated both the extent of the variation in weight of stool samples prepared by the Kato-Katz method and its influenced on egg counts and commonly used group parameters of infection derived from them. In a first study group of 795 people, the total mean weight of stool aliquots, prepared with templates designed to contain 28.3 mm3, was 23.0 mg with 95% of the individual values lying between 12.0 and 34.0 mg. Minimum and maximum values were 2.4 and 49.5 mg, respectively. Frequency distributions of the individual weights, in series of slides prepared by different laboratory assistants, showed significant differences. In a second study group of 199 people, duplicate series of slides were prepared and variations in the weight of examined stool were related to variations in egg count. The correlation between repeated individual sample weights in this series was poor, but the correlation between eggs counts was good. This was translated, at aggregate level, in very similar classifications in egg count categories. This classification was also hardly influenced by the choice of the conversion factor to transform eggs counts per slide into eggs per gram. At the individual level, the variability in egg counts far outweighed the variability in sample weight and was not clearly related to it. We therefore concluded that variations in weight of examined stool are considerable, but account for only a minimal part of the important egg count fluctuations generally observed.

Adult↗
PubMed1997

Intraspecimen fecal egg count variation in Schistosoma mansoni infection.

To determine the degree of intraspecimen fecal egg count variation in Schistosoma mansoni infection and its impact on commonly used parasitologic parameters obtained by single egg counts, 10 25-mg Kato-Katz slides were prepared from each of three stool specimens collected on different days in a study group of 20 infected people. Individual fecal egg counts in these series of examinations varied considerably and this had profound consequences for the reliability of both qualitative and quantitative diagnosis. In light infections, S. mansoni eggs in stools appeared to be homogeneously mixed. However, this distribution became heterogeneous as the intensity of infection increased, indicating clustering of eggs in stool. The cumulative egg counts in the 10 slides of the same 20 people examined in this study were compared with those in 14 slides prepared from seven stool samples collected on different days. This revealed significantly different mean egg counts for six people, even after such exhaustive series of examinations. Intraspecimen variation also biased considerably some operational parameters used to determine the infection status at the group level, particularly when these were determined by the examination of single 25-mg slides. The examination of duplicate or multiple slides improved the intraspecimen estimates of these parameters but did not overcome day-to-day variation. The examination of fewer samples taken on different days proved to be more adequate than examining more slides from one stool specimen for the determination of precise estimates of the real infection status.

Adolescent↗