Comparison of the Kato-Katz technique, hatching test and indirect hemagglutination assay (IHA) for the diagnosis of Schistosoma japonicum infection in China.

The Kato-Katz technique (duplicate 41.7 mg fecal smears), hatching test and indirect hemagglutination assay (IHA) were compared for their ability to detect human Schistosoma japonicum infection in two endemic villages (Zhonjiang and Zhuxi) in rural China. The hatching test (using a nylon bag, and based on about 30 g of feces) and IHA are conventional Chinese diagnostic methods. In both villages, the trends of prevalences with age and sex were comparable for the different methods. In Zhuxi, Kato-Katz examinations of stools from 7 different days and hatching were available, which could be used as a reliable gold standard. This resulted for IHA in a sensitivity of 80% and a specificity of 48%. The sensitivity of the Kato-Katz technique using one stool specimen was 68%, twice that of hatching (33%). In Zhonjiang, however, hatching resulted in more positive cases than Kato-Katz (prevalence 31% vs. 24%). Apparently, the result of the hatching test depends on environmental factors such as temperature and water quality. Although imperfect, Kato-Katz is recommended out of the three evaluated techniques as the method of choice for large-scale screening of S. japonicum. Hatching is much more tedious, provides inconsistent and only qualitative results, and is not much more sensitive than Kato-Katz. Its poor specificity makes IHA unsuitable for individual screening, but it may be more effective for community diagnosis.

Uncertainties in the epidemiology and control of schistosomiasis.

In this paper, gaps in our understanding of the dynamics of infection, transmission, pathology, and control of schistosomiasis, and the possible contribution of modeling are briefly discussed. The measurement of prevalences and intensities of infection by egg counts has shortcomings; a recently developed model of egg count variations contributes to a better interpretation of survey data, and suggests that true prevalences and worm loads in endemic communities may be considerably underestimated. The question as to whether schistosome populations are regulated by host-dependent or transmission-related factors is still being debated; recent scientific advances and operational control experiences tend to favor the first mechanism, with important implications for control and research strategies. However, there is still a lack of field data to feed models of the dynamics of transmission. We still know little about the dynamics and even the importance of schistosomiasis morbidity, although more objective data are now becoming available through ultrasound studies. Models of the development of early- and late-stage morbidity could substantially contribute to more cost-effective strategies of passive and active chemotherapy. Modeling can also contribute to a better understanding and improvement of results of ongoing control efforts, particularly concerning the impact of repeated chemotherapy, and its complex interaction with many biological and social factors on infection, transmission, and morbidity.

Day-to-day egg count fluctuation in Schistosoma mansoni infection and its operational implications.

In a study group of 183 people in a Schistosoma mansoni-endemic area in Burundi, stool examinations were performed with duplicate 25-mg Kato-Katz slides on seven occasions (days 1, 3, 5, 8, 10, 32, and 37). Point prevalences detected by single examinations of 25 mg and 50 mg of stool varied from 41.0% to 57.9% and from 55.7% to 63.9%, respectively. The cumulative prevalence for all seven measurements was 82.0%. The individual day-to-day variation in egg output was important. The majority of infections missed by the examination of single slides and specimens were light ones. The Kato-Katz method applied on a single stool specimen is more suitable for morbidity control, but less suitable for control of infection. When a precise quantitative diagnosis on the individual level is required, several measurements on different days are necessary. The data presented validate recently developed statistical models and charts predicting true prevalences.

Impact of repeated community-based selective chemotherapy on morbidity due to schistosomiasis mansoni.

The impact of repeated chemotherapy on morbidity due to schistosomiasis mansoni was evaluated in Gihungwe (initial prevalence 58%) and Buhandagaza/Kizina (33%), two village clusters in Burundi. Surveys were carried out with reference to the first treatment (month 0) at months -6, -3, 0, 3, 6, 9, 12, 24, and 36. Praziquantel (40 mg/kg) was given at months 0, 12, 24, and 36 to those showing eggs in the feces with a single 28-mg Kato slide. At each survey, duplicate Kato smears were examined, and all participants responded to a standardized medical history interview and underwent a clinical examination. In the three preintervention surveys, spleen and liver rates remained stable at the community and the individual level. The frequencies of diarrhea and abdominal pain varied to some extent, but they were consistently higher in the most heavily infected villages and age groups and remained relatively stable at the individual level. At the final survey, the prevalence of infection had decreased to 25%, and the frequency of diarrhea from 19-26% to 10% in both village clusters. This impact was strongest in the younger age groups. The frequency of abdominal pain was reduced only at the short term and in selected age groups. Organomegaly decreased only to a limited extent in those treated, and increased in those not treated, possibly due to the impact of malaria. The net result was that no measurable impact of the treatments on organomegaly at the community level could be demonstrated. In the light of these results, the relevance of community-based chemotherapy in moderate foci is questioned.

Repeated community-based chemotherapy for the control of Schistosoma mansoni: effect of screening and selective treatment on prevalences and intensities of infection.

The impact of repeated selective chemotherapy on prevalences and intensities of infection with Schistosoma mansoni was evaluated in Gihungwe Transversals 1 and 2 (initial prevalence 60%) and Buhandagaza/Kizina (initial prevalence 35%), two village clusters in Burundi. Surveys were carried out at months -6, -3, 0, 3, 6, 9, 12, 24, and 36, with reference to the first intervention; treatment with praziquantel (40 mg/kg) was given at months 0, 12, 24, and 36 to subjects showing parasite eggs on a single 28-mg Kato slide. A second slide was examined for monitoring purposes only. Over the pre-intervention period, the overall prevalences and intensities remained relatively stable, but important increases were observed in specific groups. The cure rate three months after the first treatment in those treated was 73% (Gihungwe) and 83% (Buhandagaza/Kizina), but the prevalence at the community level was reduced only by 50% and 46%, respectively. Fifty-six percent and 79%, respectively, of the remaining positive cases had not been treated, largely because they were (falsely) negative at the screening. Reinfection occurred mainly in Gihungwe and in younger age groups. One year after the second treatment, prevalences and intensities were further reduced in Gihungwe only; one year after the third treatment prevalences were not reduced further in either village group. The final prevalence of infection was approximately 25%, with infections with an intensity of over 100 eggs per gram of feces approximately 5%, in all four villages. Over 80% of the remaining cases had not been treated at the previous intervention; the sensitivity of the screening method appears to be a major determinant of the outcome of repeated selective treatment.

Assessing the public health importance of Schistosoma mansoni in different endemic areas: attributable fraction estimates as an approach.

Assessment of the public health importance of schistosomiasis mansoni is hampered by the nonspecificity of many of its disease symptoms. Parasitologic, clinical, and anamnestic data from two areas in Burundi were used to obtain estimates of the attributable fractions for different disease symptoms at both the population level and within different age strata. A large proportion of individuals had symptoms commonly associated with Schistosoma mansoni infection that were not attributable to this parasite. The clinical indicator with the best test efficiency was shown to be bloody diarrhea. At the population level, 35% of bloody diarrhea cases were attributable to S. mansoni, compared with only 9% of diarrhea cases without blood. The attributable fractions were age-dependent, and in the case of diarrhea (with and without blood), children had a higher proportion of cases attributable to S. mansoni infection than adults. The association between infection and disease symptoms also increased with the intensity of infection. The prevalence of morbidity attributable to S. mansoni was similar for all symptoms, and higher in children than adults. The estimation of attributable fractions provides a simple approach to quantify S. mansoni-related morbidity, which could also be extended to both S. haematobium and S. japonicum. Attributable fraction estimates for these three schistosome species in different endemic areas would greatly aid in the assessment of the health burden of this parasite and the effectiveness of control programs.

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.

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.

Antibody response to Schistosoma mansoni adult worm cysteine proteinases in infected individuals.

Antigens of the Schistosoma mansoni digestive tract are recognized early in the infective process. Two immunogenic components of the excretory/secretory products are proteolytic enzymes that degrade host hemoglobin in the lumen of the parasite gut. These enzymes, CP1 and CP2, belong to the class of cysteine proteinases. In this study, a preparation containing both proteinases has been used to detect proteinase antibodies in the sera of individuals living in Burundi. Of 133 individuals tested, 92% were excreting schistosome eggs. All patients with documented infections had positive anti-proteinase IgG titers (mean = 1:614), while 82% had positive IgM titers (mean = 1:267). Six weeks following praziquantel treatment, patients were assessed for egg excretion and antibody titer. Anti-proteinase IgG titers were significantly lower (mean = 1:259) than pre-treatment titers. Patients who were infected with S. japonicum or S. haematobium typically showed a cross-reactive IgG response. Patients from non-endemic regions yielded negative titers, and those with non-trematode parasites were negative (79%) or weakly positive. S. mansoni cysteine proteinases may be used for the detection of schistosome infections.

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.

Fluctuation of schistosome circulating antigen levels in urine of individuals with Schistosoma mansoni infection in Burundi.

We studied the fluctuations of schistosome circulating antigens in urine as compared with fecal egg counts in 60 Burundese individuals infected with Schistosoma mansoni. Levels of circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) in the urine were determined by quantitative enzyme-linked immunosorbent assays. Fecal samples were simultaneously collected and examined with duplicate Kato-Katz slides. Significant correlations were consistently found between circulating antigen levels in urine and fecal egg counts. Although both antigen levels and egg output fluctuated, there was less fluctuation of CCA levels in urine than of fecal egg counts. All individuals had CCA in at least one urine sample and 82% were at least once positive for egg counts. Positive CCA levels were found in at least one urine sample in 75% of all individuals, but levels were low. Our results show that detection of CCA in urine is a sensitive, quantitative, and reliable method for noninvasive diagnosis and screening of S. mansoni infections, due to the relatively low fluctuations.

Variations in fecal Schistosoma japonicum egg counts.

Variations in fecal Schistosoma japonicum egg counts were studied in ZhuXi administrative village, JiangXi Province, China. Population stool examinations were collected with duplicate, standard, 41.5-mg Kato-Katz thick smears on seven consecutive days for 570 individuals from two natural (individual) villages: village I with high endemicity and village II with low endemicity. The proportion of individuals with at least one positive count increased from 42.4% after a single measurement to 68.3% after seven measurements in village I (n = 356), and from 17.0% to 36.0% in village II (n = 214), respectively. This demonstrates a very high variation in repeated S. japonicum egg counts and a considerable lack of sensitivity of the Kato-Katz technique; light and moderate infections are especially missed with a single or a few measurements. The observed day-to-day variation in individual egg counts is highly aggregated (variance higher than the mean) and suggestive of a negative binomial distribution. For five individuals on three days, repeated sampling from different locations of a stool specimen shows a clear trend with egg counts decreasing from the beginning of the stool to the end and from the outside layer to the center. Ten multiple samples from a particular subsection (10-30 g) of a stool specimen for 44 positive individuals still showed aggregation in egg counts, particularly for high intensities of infection. This means that the aggregation in repeated daily S. japonicum egg counts cannot be explained alone by a specific day-to-day component and variation in the concentration of eggs at different locations in the stool. There also exists clustering of eggs within parts of the stool.

Epidemiologic application of circulating antigen detection in a recent Schistosoma mansoni focus in northern Senegal.

Quantitative enzyme-linked immunosorbent assays (ELISAs) for the detection of circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) in serum and urine were applied as an epidemiologic tool in a recent, intense focus of Schistosoma mansoni in Senegal. Both CAA and CCA in serum and CCA in urine were found in 94%, 83%, and 95%, respectively, of the population, of which 91% were positive on stool examination. Circulating antigens were also detectable in sera and urines of most egg-negative individuals. The sensitivities of the urine CCA and serum CAA ELISA were substantially higher than that of a single egg count, and increased with egg output. The CAA and CCA levels correlated well with egg counts and with each other. The age-related evolution of antigen levels followed a similar pattern as egg counts, providing supplementary evidence for a genuine reduction of worm burdens in adults in spite of the supposed absence of acquired immunity in this recently exposed community. The antigen:egg ratios decreased in adults, suggesting lower worm fecundity in children. This would be compatible with a density-dependent reduction of fecundity, but not with anti-fecundity immunity in adults that perhaps has not yet developed in this new focus.

Efficacy and side effects of praziquantel in an epidemic focus of Schistosoma mansoni.

Schistosoma mansoni was first reported in the area of Richard Toll (Senegal) in 1988 and spread rapidly in the community, after a series of human-engineered ecologic changes. A random population sample (n = 422) from Ndombo, a village near Richard-Toll, was studied in 1991 by stool examination (four Kato slides from two stool samples) and antigen detection in urine and blood. Stool-positive individuals were treated with 40 mg/kg of praziquantel. A house-to-house interview regarding side effects was conducted 24 hr after treatment. Two hundred ninety-eight subjects were re-examined 10 days (antigen detection) and 12 weeks (egg counts, antigen detection) after treatment. Before treatment, positive egg counts were found in 91% of the subjects, with 41% excreting more than 1,000 eggs per gram (epg) of feces. Treatment of 352 individuals caused serious but transient side effects (colic, vomiting, urticaria, and edema), the frequency of which increased with increasing egg counts. The parasitologic cure rate 12 weeks after treatment was only 18%, the frequency of egg counts with more than 1,000 epg decreased to 5%, and the mean egg count of those remaining positive was reduced by 86%. Antigen detection in serum 10 days and 12 weeks after treatment remained positive in 90% of the subjects, although titers decreased sharply. The low cure rates may be due to intense transmission and/or undeveloped immune responses in this recently exposed population. However, reduced drug susceptibility of the parasite strain has now been confirmed in one local isolate.

Epidemiology of Schistosoma mansoni infection in a recently exposed community in northern Senegal.

The epidemiology of Schistosoma mansoni infection was investigated in Ndombo, a village in the epicenter of a very recent outbreak of schistosomiasis in northern Senegal. Repeated fecal egg counts and antigen detection in urine and serum were carried out in a random population sample (n = 422). Eggs were found in 91% of the subjects, with 41% excreting > 1,000 eggs per gram of feces (epg) (mean egg load of 646 epg). The prevalence was almost 100% in groups greater than five years of age. In spite of the supposed absence of acquired immunity, intensities of infection decreased strongly in adults. Antigen detection confirmed the high prevalence and intensity of infection and the age-related distribution of worm loads. The emergence of this new focus is probably due to the ecologic impact of newly built dams and the extension of irrigation projects in the Senegal basin.

Therapeutic evaluation of two different dose regimens of praziquantel in a recent Schistosoma mansoni focus in Northern Senegal.

A therapeutic trial, involving 130 Schistosoma mansoni-infected children, with no previous history of antischistosomal treatment, was carried out to evaluate the efficacy of two different dose regimens of praziquantel. The study was carried out because low cure rates were described in this recently established (1990) S. mansoni focus in northern Senegal, following treatment with a standard dosage of 40 mg/kg. The subjects were randomly allocated into two groups: one group (1) received 40 mg/kg in one oral dose, the other group (2) was treated with two oral doses of 30 mg/kg at a 6-hr interval. Parasitologic examination and circulating anodic antigen (CAA) detection were performed before, 10 days, three, six, and 21 weeks after chemotherapy. No significant differences in cure rates were found between the two groups. Six weeks after treatment, 34% and 44% of the individuals were found to be stool negative in group 1 and group 2, respectively. However, only 10-15% became completely negative according to the serum CAA antigen assay. Mean egg counts were reduced by 99% in both groups. Antigen detection confirmed the parasitologic results. Fewer side effects were observed in the group treated with 2 x 30 mg/kg, which may be explained by split dosage administration. Our study shows that the low cure rates observed in this area could not be improved by using a higher dosage of praziquantel.

SCHISTOSIM: a microsimulation model for the epidemiology and control of schistosomiasis.

A computer simulation model, SCHISTOSIM, has been developed for the epidemiology and control of schistosomiasis, based on the stochastic microsimulation technique. The eventual aim is to evaluate and predict the effects of different control strategies. In the current state of the model, human-, worm-, and infection-related aspects have been included. However, many others, including most transmission and transmission-related mechanisms, have yet to be modeled. By simulating a series of surveys and treatments in Burundi, short-term effects of this program were satisfactorily explained by the model. However, long-term predictions did not match the observed data. Possible extensions of the model to properly describe these effects are identified. The potential of SCHISTOSIM as a tool for the prediction of outcomes of alternative control strategies is illustrated and discussed.

Organometric investigations of the spleen and liver by ultrasound in Schistosoma mansoni endemic and nonendemic villages in Senegal.

With the intention of ultrasonographically assessing hepatosplenic morbidity in Schistosoma mansoni infection and of validating the grading system applied (Cairo classification), 191 subjects in a schistosomiasis endemic village and 247 controls from a nonendemic village in northern Senegal underwent sonographic examination of the liver and spleen. Measurements of the diameters of the peripheral periportal vein branches, the main portal vein stem, liver size (left lobe and right lobe), and spleen length in the endemic village were compared with those in the nonendemic village to evaluate the much discussed influence of S. mansoni infection on those variables. To subtract this presumed influence from reference values for the named variables, they are given as measured in the nonendemic village, stratified by body weight, enabling future investigators on schistosomiasis-induced morbidity to refer to these reference values. The 95th percentile regarding peripheral periportal vein branch diameter in the control groups was exceeded in 24% of the subjects in the endemic group. It was exceeded by 6% for the main portal vein stem diameter, 13% for the left liver lobe, 12% for the right liver lobe, and 14% for the spleen length. According to the Cairo classification, 97% of the endemic population and 81% of the controls had periportal thickening of the liver, mostly grade I. We conclude that 1) hepatic morbidity in the S. mansoni endemic area was low, despite strikingly high intensities of infection; 2) the Cairo classification in its present form overestimates periportal thickening, especially in the case of mild morbidity; and 3) body height-dependent reference values, obtained from endemic controls, must be applied for organometric parameters.

The contribution of host-related factors to low cure rates of praziquantel for the treatment of Schistosoma mansoni in Senegal.

Surprisingly low cure rates were repeatedly observed after treatment with a standard dosage of praziquantel in a recently established Schistosoma mansoni focus in northern Senegal. In 4 discrete cohorts from the same population, cure rates were 18-36% and egg count reduction rates were 77-88%. Data and material of 920 compliant subjects from all 4 cohorts were further analyzed to identify possible host-related factors associated with low cure rates. The lowest cure rates were found in the highest egg count groups. However, in low and moderate egg count groups, drug efficacy was also below normal values. Cure rates were similar in males and females, showed no seasonal variation, and were independent of previous praziquantel treatment. They were significantly higher in adults than in children, also after allowing for intensity of infection. Individual water contact behavior and specific humoral immune responses were examined in 2 extreme subgroups, either without significant egg count reduction or showing complete parasitologic cure. There was no significant difference in frequency and duration of water contact between those individuals with complete cure and those that showed little effect of praziquantel treatment. Levels of IgG, IgG1, IgG3, IgG4, IgM, and IgE against adult worm antigen were not different between the 2 subgroups. Thus, the abnormally frequent failure of treatment observed in this focus could not be associated with any host-related factor, other than age and pretreatment egg counts.

Ultrasonography in a Senegalese community recently exposed to Schistosoma mansoni infection.

Inhabitants of Ndombo (n = 614), a village in an area recently infected with Schistosoma mansoni in Northern Senegal, were examined clinically, parasitologically, and ultrasonographically to investigate the presence and degree of S. mansoni-related hepatosplenic morbidity after a few years of exposure to schistosomal infection of regional canals. Despite previous praziquantel treatment of 56% of the inhabitants prior to our investigation, the prevalence of S. mansoni infection in 1993 was 90%, and 42% of the villagers excreted more than 1,000 eggs per gram of stool. Previously untreated individuals were found to have significantly higher egg counts than treated ones. Despite the high intensities of infection, ultrasonographically detected severe periportal thickening of the liver was infrequent. Grading according to body length-dependent normal values of cross-section diameter of peripheral portal vein branches of a European control group correlated with intensities of infection. Of the total group of patients, 30% (n = 182) had more severe thickening of portal vein branch diameters above the 97th percentile and 70% of these had a splenomegaly. The highest egg counts and the most frequent development of periportal thickening were found in 11-20 year-old individuals. Periportal thickening was less frequent in praziquantel-treated adolescents than in untreated ones. This suggests that early antischistosomal medication may be useful to limit schistosomiasis-induced hepatic morbidity especially in children, even though reinfection seems inevitable.