Morbidity in Schistosomiasis: Assessment, Mechanisms and Control

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Morbidity in Schistosomiasis: Assessment, Mechanisms and Control B.J. Vennervald, J.H. Ouma and A.E. Butterworth Nyeri, Kenya November 1997 In spite of the availability and use of safe and effective drugs for the treatment of schistosomiasis in national control programmes, schistosome infection remains prevalent throughout much of sub-Saharan Africa, and is possibly increasing as a result of the introduction of water development schemes. WHO currently estimates that, out of 200 million people with schistosomiasis, 150 million live in Africa. Schistosomiasis, as a public health problem, has received relatively little attention, largely because the clinical consequences are chronic in nature, variable in severity (only 10% of those with schistosomiasis are seriously affected), and difficult for clinician and patient to diagnose. This workshop addressed the assessment of schistosome morbidity, the mechanisms whereby morbidity may be variably expressed in individuals with comparable intensities of infection, and the control of morbidity at the operational level. A number of issues recurred throughout the workshop. Niels Christensen (Danish Bilharziasis Laboratory, Denmark) stressed the need for balance between basic and applied, and biomedical and social research, and of establishing the impact of schistosomeassociated morbidity on the community. Schistosomiasis must be considered as part of an overall pattern of health and disease in the community. Birgitte Vennervald (DBL, Denmark) distinguished between severe, direct, organspecific, clinical disease, and the milder, nonspecific manifestations that may be equally important at the community level. Both John Ouma (Division of Vector Borne Diseases, Kenya) and Christoph Hatz (Swiss Tropical Institute, Switzerland) emphasized the need for integration of research within control, and of schistosomiasis control with other public health problems, including intestinal nematodes and malaria. Assessment of Schistosomeassociated Morbidity The application of ultrasonography to epidemiological studies of schistosomiasis morbidity in the field represents a Parasitology Today, vol. 14, no. 10, 1998

major advance, although its value varies according to the species of schistosome. Although ultrasonography required careful interpretation as a ‘snapshot’ of a dynamic process, it could be sensitive, specific, acceptable to the community and to individual patients, and effective both in assessing morbidity for the planning of control programmes and as a research tool to gather data about the pathogenesis of disease and the regression and reappearance of morbidity after treatment. Hatz emphasized the importance of standardization of protocols and records, observer variation, and the need to compare results from different settings. He described in detail the results from a cohort of schoolchildren with Schistosoma haematobium infection in Ifakara, Tanzania, who were examined before and at intervals after treatment. Before treatment, ultrasonographic changes in the bladder wall, ureters and kidneys correlated well with intensities of infections as estimated by urinary egg counts, and with other markers of morbidity. After treatment with praziquantel, egg counts fell rapidly within two months: ultrasonographically detectable lesions of all grades of severity in the bladder and in the kidneys also declined, but somewhat more slowly, reaching a nadir six months after treatment. Thereafter, lesions reappeared over the subsequent 18 months, as the children became reinfected. In this area, therefore, treatment of schoolchildren at intervals of not less than two years might be sufficient to control morbidity. Ultrasonography in S. mansoni infection is less clear-cut; there is still controversy about standardization of examination and recording of results. It is especially valuable in the identification of established periportal fibrosis that may lead to portal hypertension, the development of oesophageal varices and gastrointestinal haemorrhage. It is also useful in validating results obtained by simple clinical examination. It is currently less effective in the specific identification and grading of early or minor lesions: this would be particularly advantageous in mechanistic studies on the initiation and progression of disease, and in studies (analogous to those described for S. haematobium) on the regression of morbidity following treatment. Two

approaches to this problem were presented. Joachim Richter (Institute of Tropical Medicine, Berlin, Germany) described findings from an age-stratified cohort of individuals from a heavily exposed fishing community in Butiaba on Lake Albert, Uganda, in which a high prevalence of severe clinical disease was observed. One-third had established periportal fibrosis, often associated with signs of portal hypertension. A further 22% had less specific changes. A series of ‘Butiaba image patterns’ was established with the aim of rapid classification of the severity of periportal fibrosis. Patterns were included that possibly reflect more subtle changes. Although it was not possible to be certain in which order the observed changes occurred, interobserver correlation was good, and the process rapid: an important benefit in field epidemiological studies. Another approach, described by Mats Asztély (University of Göteborg, Sweden) from a study on Kome, a Tanzanian island in Lake Victoria, observed altered echogenicity of the portal vessel walls, perhaps reflecting inflammatory changes that precede fibrosis. In the case of S. japonicum infections in the Philippines, Rüdiger Kardorff (Medical School, Hannover, Germany) described two types of lesion. The first, a typical periportal fibrosis, was associated with reduced portal venous blood flow velocity, as detected by Doppler ultrasonography; the second, a fibrous network anatomically separate from the portal branch, was not associated with changes in portal venous blood flow, but with cholestasis and enzyme changes indicative of liver damage. Both types of lesion were observed in adults from an area where annual chemotherapy of infected individuals had taken place for many years, which may suggest that fibrosis in S. japonicum infections is less rapidly reversed by treatment than is fibrosis in S. haematobium and possibly S. mansoni infections. Gabriel Mbugua (Kenya Medical Research Institute, Kenya) also addressed reversibility. A clinical study from an area of high S. mansoni morbidity near Kambu, Kenya, of a cohort of schoolchildren with severe hepatosplenomegaly (as detected by palpation) revealed a slow decline in the prevalence

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News and severity of hepatosplenomegaly after repeated annual treatment with praziquantel. A similar slow regression, over at least five years, was closely followed in 14 children with very severe disease. Further clinical observations were presented by Gabriele Poggensee (Institute of Tropical Medicine, Berlin, Germany) and by Lars-Åke Nilsson (University of Göteborg, Sweden) on behalf of Reverianus Gabone (National Institute for Medical Research, Mwanza, Tanzania). Poggensee concentrated on the important problem of female genital schistosomiasis (FGS), a syndrome that has been recognized since 1899, but largely ignored. In a study in Mwanga District, Tanzania, gynaecological examinations with biopsy and colposcopy were carried out in women whose urinary excretion of S. haematobium eggs was also recorded. Eggs in the urine were detected in 40% of women, and FGS (as defined by the detection of eggs in crushed biopsy specimens) in 32%. However, the age–prevalence curves differed, with urinary eggs declining from age 15 years onwards, and FGS reaching a peak at 25–29 years: in 38% of patients with FGS, no eggs were detected in the urine. FGS was associated with significant gynaecological symptoms, and is considered as an important aspect of S. haematobium morbidity, as well as a possible risk factor for HIV infection: in discussion, the need was stressed for a diagnostic method that does not depend on gynaecological examination and biopsy. The possible importance of male genital schistosomiasis as a risk factor for HIV infection was outlined by Hatz. Also in Tanzania, Nilsson described extensive studies from Kome Island in Lake Victoria on different approaches to control S. mansoni infection and morbidity through different regimens of administration of praziquantel, including annual versus sixmonthly treatments, mass chemotherapy versus treatment of schoolchildren, and the use of 20 instead of 40 mg kg21 praziquantel doses, which raised interesting questions about the practical issues of compliance and immigration in operational control programmes. Participants then turned to other markers of morbidity. Since intensity of infection is a key determinant of morbidity, it is important to be able to measure intensity accurately and to develop markers that are true indicators of morbidity, not simply surrogate estimates of intensity. Tony Fulford (University of Cambridge, UK) and Dirk Engels (Prince Leopold Institute of Tropical Medicine, Antwerp, Belgium) both described the very high level of variation in egg counts 386

that occurs both within, and (more importantly) between, stool samples in the case of S. mansoni: a similar variation has been reported for S. japonicum, and for urinary egg counts in the case of S. haematobium. Such variation leads not only to imprecision in the estimation of egg counts (and hence loss of information), but also to inaccuracy in estimation (as a consequence of regression to the mean), to incomplete allowance for the confounding influence of intensity of infection in analysis of other variables, and to poorly matched experimental pairs. Fulford stressed the importance of replicate measurements, not only in improving accuracy, but also in estimating the size of the problem, and evaluating the error. This may be achieved by Markov Chain Monte Carlo simulations or by simpler techniques that allow comparison of otherwise dissimilar populations. Engels described the high level of fluctuation of faecal eggs with time. This can lead to variation in mean egg counts, even when multiple samples are taken. He concluded that, although it is desirable to take as many samples as possible, in large-scale field studies, examination of duplicate preparations from three separate samples is probably sufficient. The variability in egg counts, as well as the fact that they are only indirect estimates of adult worm burden and may lead to incorrect conclusions if, for example, adult worm fecundity is suppressed, has led to a search for alternative measurements of worm burden. André Deelder (University of Leiden, The Netherlands) reviewed the measurement of two circulating adult worm antigens, CAA (circulating anodic antigen) and CCA (circulating cathodic antigen), in the blood and urine by ELISA (enzyme linked immunosorbent assay)based assays. Such assays are sensitive, specific, and much less variable than egg counts. Production of the relevant monoclonal antibodies (mAbs) has recently been scaled up, and Robert Bergquist and Lester Chitsulo (WHO, Geneva, Switzerland) expressed enthusiasm for their more widespread use and a commitment by TDR to facilitate and fund dissemination of the reagents. Deelder gave a number of examples in which circulating antigen measurements have proved more useful than egg counts, including: (1) the demonstration of infection in children under four years old in the Kome study from Tanzania; (2) the demonstration of suppression of egg excretion in older individuals infected with S. haematobium, but not S. mansoni; and (3) the demonstration that Brazilian patients with hepatosplenic disease have

higher circulating antigen levels for a given faecal egg output than those without. He also described a study on S. haematobium in Cameroon in which circulating antigen levels and egg counts yielded conflicting results. In a cohort of children, one month after praziquantel treatment, mean egg counts fell to very low levels, followed by a rise after 12 months, suggestive of reinfection. In contrast, antigen levels fell only to a plateau level one month after treatment, and by 12 months, had risen to pretreatment levels, suggesting that the effect of treatment was temporarily to suppress egg output rather than to kill the worms. Subsequently, Nilsson described the use of the circulating antigen assay in the control programme on Kome Island in Tanzania (see above), as an example of its application in large-scale epidemiological studies. Both prevalence and intensity of infection fell less after treatment when estimated by CAA levels than when estimated by egg counts. Anthony Kahama (University of Leiden, The Netherlands) described an assay for urinary soluble egg antigens (SEA) as a marker of morbidity in S. haematobium infection. In a cohort of Kenyan schoolchildren, pretreatment urinary SEA was correlated both with egg counts and with morbidity, as detected both by haematuria and by ultrasonography. After treatment, urinary egg counts fell rapidly, while urinary SEA levels fell more slowly and in parallel with the decline in ultrasonographically detectable lesions. As reinfection occurred, urinary SEA levels rose in parallel with the reappearance of lesions, and at one time point remained significantly associated with morbidity, as determined by ultrasonography even after controlling for age, sex and intensity of infection. Claus M. Reimert (National Hospital of Denmark, Copenhagen) described the development, standardization and application of an assay for eosinophil cationic protein (ECP) in urine, as a marker for eosinophilic responses against eggs in the bladder. ECP in urine samples remained stable after storage and, unlike egg counts, showed little circadian or diurnal variation. In the Ifakara cohort of schoolchildren described earlier by Hatz, urinary ECP levels were correlated before treatment with both the presence and severity of bladder lesions detected by ultrasonography. After treatment, ECP levels fell more slowly than did egg counts, and paralleled the decline in bladder pathology. However, as reinfection occurred, bladder pathology had started to reappear 12 months after treatment. Urinary ECP also reappeared Parasitology Today, vol. 14, no. 10, 1998

News in concordance with reinfection and pathology, but at a much reduced level compared to pretreatment levels. By 18 months after treatment, ECP levels reached the pretreatment levels, indicating that this assay is promising as a robust, non-invasive and sensitive marker of morbidity. In parallel studies of Tanzanian children, Vennervald measured various cytokines in the urine of children infected with S. haematobium, before and after treatment. Interleukins IL-6 and IL-8, but not TNF (tumour necrosis factor), could be detected in pretreatment samples, and disappeared extremely rapidly (within 24 h) after treatment: the reason for this remains uncertain. Subsequently, in Kenyan schoolchildren, cytokine levels were correlated with intensity of infection and with morbidity, as detected both by micro- and macrohaematuria and by ultrasonography. Finally, Hassan Mshinda (Ifakara, Tanzania) pointed out that detection of microhaematuria (by dipstick) remained a simple marker for morbidity that could be applied in operational control programmes at the community level. The relative lack of consensus about the early ultrasonographic changes in S. mansoni infection means that biochemical markers of early morbidity would be especially useful. Kardorff reviewed the measurement of collagen and connective tissue precursors and breakdown products and described a study on Ukerewe Island in Lake Victoria where the prevalence and intensity of S. mansoni infections were high, and associated with a 6% prevalence of severe (grade II or III) fibrosis. He found an increase in circulating N-terminal procollagen-III-peptide (PIIIP), C-terminal procollagen-IV-peptide (NC1) and laminin P1 peptides in 13–55% of patients. PIIIP and laminin P1 showed no correlation with ultrasonographic findings, but NC1 showed significant correlations with Grade II/III fibrosis and the presence of collaterals. He attributed the relatively weak performance of the marker to the fact that, whereas ultrasonography or histology gives a crosssectional, static view of the disease process, collagen peptide levels reflect a dynamic process of synthesis and degradation, modified by changes in liver function, portal hypertension with porto–systemic shunts, and extrahepatic disease. Further work is needed to exclude confounding influences and to search for markers of early morbidity and their changes after chemotherapy, and for markers that predict, rather than reflect, severe disease. Parasitology Today, vol. 14, no. 10, 1998

Pathogenic Mechanisms – in Pigs, Mice and Men The mechanisms involved in the pathogenesis of disease, and the possible reasons for the variability between individuals in disease severity were explored. As David Dunne (University of Cambridge, UK) pointed out, infection often leads to low-grade morbidity, which may then either regress spontaneously or progress to more severe disease: each process may be affected by physiological and immunoregulatory mechanisms, which may in turn be affected by environmental or genetic influences. Studies in animal models, which can undergo experimental manipulations, can provide indications for correlative studies in humans. Niels Christensen described the use of the Danish pig (Danish Landrace/ Yorkshire/Duroc crossbred pigs) as a model of S. japonicum infection and pathology, the pig being a natural host in China and the Philippines. Experiments in large animals required the development of new techniques, including the production and labelling of S. japonicum cercariae, infection of animals, adult worm recovery and tissue egg counts. In particular, worms tended to become trapped in the mesenteric veins and had to be recovered manually, a problem that could be partially overcome by treating the animal with praziquantel one hour before perfusion. Percentage establishment of worm pairs following either percutaneous or intramuscular infection with cercariae was low, and animals self-cured, with both recoverable worms and faecal and tissue eggs declining sharply by 14 weeks after initial infection. Animals that had rejected a primary infection were totally insusceptible to a challenge infection. Infected animals developed a significant degree of liver pathology that progressively resolved after self-cure, and the model could prove extremely valuable in further studies on heterologous interactions, host nutritional status, vaccine testing, and the regression of pathology, either spontaneously or after treatment. In recent years, the mouse model of S. mansoni infection has yielded an enormous amount of information, in particular through the use of gene knockout animals and by treatment with cytokines and anti-cytokines (Tom Wynn, National Institutes of Health, USA). Following infection of wild-type mice, or intravenous inoculation of eggs, a Th2 response to egg antigens predominates, with the formation of

eosinophil-rich granulomata and fibrosis. Partial shifting of the balance of the response towards Th1, for example by previous immunization with eggs and IL-12, leads to a reduction in both granuloma size and fibrosis in infected animals. However, polarization of the response towards Th1 (eg. in IL-4/IL-10 knockout animals) leads not only to ablation of the granulomatous response, but also to an increased early mortality. In contrast, polarization of the response towards Th2 (eg. in IL-12/IL-10 knockout animals) leads to increased fibrosis and possibly increased late mortality. IL-10, while capable of modulating the induction of both Th1 and, to a lesser extent, Th2 responses, appears not to be responsible for the spontaneous modulation of granuloma formation that is observed during chronic infection. Events that occur in the IL-4 knockouts were further discussed by Ed Pearce (Cornell University, USA). Following infection, such mice showed reduced faecal egg excretion and alterations in intestinal pathology: they became cachectic and died earlier than did wild-type animals, an event that could be delayed by treatment with anti-TNF. Pearce presented evidence that supported the hypothesis that IL-4 knockouts were more susceptible to systemic infection with Gramnegative bacteria, and that cachexia and death were attributable in part to endotoxin formation leading to TNF and NO (nitric oxide) production by macrophages. However, prevention of NO production by aminoguanidine, an inhibitor of iNOS (induced nitric oxide synthase), led to accelerated weight loss and death from acute liver failure, suggesting that the effects of NO were to protect liver cells from TNF-mediated damage. Participants were reminded that Tcell deficient mice die from the hepatotoxic effects of an egg toxin. The granulomatous reaction can therefore be viewed as a double-edged sword, protecting the host from egg hepatotoxins, but also leading to fibrosis and chronic disease. It was speculated that the wildtype mouse, and more strikingly, the mouse vaccinated with egg antigens and IL-12, are in a state of optimal balance between Th1- and Th2-cell responses, and that a polar shift in either direction leads to more-severe disease and increased mortality. This might have implications for human infection, where the majority of individuals are well adapted, suffering little morbidity, while only a minority go on to suffer severe disease. It is possible that the balance of the cellular immune response might be disturbed in this minority. 387

News Joseph Mwatha (Kenya Medical Research Institute) described a study of immune responses in children with or without severe clinical hepatosplenic disease. Fulford had previously discussed principle components analysis as a valuable method, when used with care, to analyse the results of such studies. In situations in which many variables are measured, but only a few underlying phenomena are suspected, principle components analysis serves to reduce the dimensionality of the data. From the data, new variables are constructed that satisfy the conditions that they are linear combinations of the original variables, that they are orthogonal to each other, and that the distances between individual data points is unaffected. Effectively, the axes of a multidimensional cluster of points are rotated until one axis has the maximum variance: other axes are then identified that are orthogonal to the first. The resulting principle components can then be conventionally analysed and their structure inspected. The method is datadriven, avoids the imposition of a model, and is applicable to a case-control design. This approach was adopted by Mwatha, who compared cellular immune responses to egg and adult worm antigens in children with the hepatosplenic disease from the high-morbidity Kambu area of Kenya, with responses in two controls, matched for age and intensity of infection but without severe disease, from Kambu and from a low-morbidity area, respectively. After allowing for area differences, hepatosplenic disease was found to be associated with a predominantly Th1-type response [high antigen-driven TNF and IFN-g (interferon gamma) production, but low IL-5], whereas lack of disease was associated with a predominantly Th2-type response (high IL-5 production, little TNF, and detectable, but lower, IFN-g). Hepatosplenic disease was also associated with the presence in the serum of markers of TNF production, including the soluble TNF receptors, sTNFR1 and sTNFR2, and ICAM-1 (internal cellular adhesion molecule 1). The implication was that individuals with hepatosplenic disease show a dysregulation of their immune responses from the well-adapted state of a predominant Th2-type response, perhaps analogous to the situation in the mouse. Patricia Ndhlovu (Blair Research Laboratory, Zimbabwe) presented work in progress on a cohort of children infected with S. haematobium, examining the relationship between morbidity, antibody responses, granuloma indices and anti-idiotypic responses. Patterns of infection were typical of an endemic 388

community, and morbidity was correlated with intensity as reflected by haematuria, proteinuria and ultrasonographic changes. Morbidity was associated with high IgG4 antibodies to SEA, and lack of morbidity with high IgE antiSEA: but the possibility could not be excluded that the IgG4 levels simply reflected intensity of infection. Of the various factors that may determine the degree of morbidity, intensity of infection is the most clear-cut and consistent. Therefore, factors that affect intensity, including exposure, immunity and other age-dependent physiological processes, will also affect morbidity. Narcis Kabatereine (Vector Control Division, Ministry of Health, Uganda) described a treatment and reinfection study in Butiaba on Lake Albert, previously referred to by Richter. This study involved a cohort of individuals, stratified by age and sex, from a heavily exposed fishing community; direct observations were made of the extent and duration of water contact, together with ancillary observations on snail infections. In contrast to previous studies, levels of water contact rose progressively with age, instead of peaking in young children. At one series of sites, on an exposed area of lake shore, this age relationship could be determined by direct observations from the shore. At a second series of sites, enclosed by reeds, there was an apparent dip in water-contact levels among young adult males. However, preliminary direct observations by canoe, revealed that many of the missing men were fishing at the outer fringes of the reeds, showing prolonged and extensive contact with water known to contain infected snails. In contrast, intensities of reinfection three and six months after treatment showed a pattern typical of other studies, with a peak at ten years of age and a decline to very low levels in older individuals. In these individuals, therefore, the lack of reinfection after treatment cannot be attributed to a lack of exposure. In terms of controlling for age-dependent changes in exposure, this study is fundamental for further studies on immunological or other physiological factors. Alain Dessein (INSERM-CNRS, Marseille, France), in discussing the influence of genetic factors on morbidity, also made the point that such factors can act either directly or indirectly by affecting intensity of infection. He presented data from Brazil, which demonstrated familial variation in susceptibility to infection, with segregation analysis yielding evidence for a single co-dominant gene controlling susceptibility or resistance, the genetic

element accounting for over 50% of the total variance in egg counts. Subsequent linkage analysis using microsatellite markers yielded a LOD score of .3 for chromosome 5q31–33, an area of the genome that encodes various immunologically active peptides, including IL-13, IL-4 and IL-5, and that is involved in the regulation of IFN-g. Cloning of T cells from resistant and susceptible homozygotes showed that resistant individuals produced more IL-4 and IL-5 than IFN-g, whereas susceptible individuals produced less. Subsequent segregation analysis of the IL-5-producing phenotype again yielded evidence for a single co-dominant gene, which is now being mapped. Dessein went on to analyse the genetics of morbidity per se, and described work in progress in the Sudan. An important issue was the identification of the affected phenotype, which was defined as either Grade III fibrosis or Grade II fibrosis, with an increased portal vein diameter. The unaffected phenotype was defined as Grade 0 or I, the remainder being categorized as ‘unknown’. Segregation analysis also provided evidence for a single codominant gene of variable penetrance, and linkage analysis is now in progress. The resistance gene might not only affect morbidity indirectly, by controlling intensity of infection, but also directly, by virtue of its immunoregulatory properties. As well as intensity of infection and genetic factors, environmental factors might also influence the impact of schistosomiasis. Ron Blanton (Case Western Reserve University, USA) discussed the impact of low intensities of infection on general health, and specifically on nutrition. Previous studies in Kenya on S. haematobium and in China and the Philippines on S. japonicum had shown an impact on nutrition, but work on S. mansoni had been less extensive. In a cohort of Brazilian schoolchildren, before treatment of S. mansoni infection, boys showed a marked reduction in heightfor-age and weight-for-age, independent of infection. Girls showed a less-marked reduction, more clearly associated with S. mansoni infection. Oxamniquine-treated boys showed more growth than did the placebo controls, an effect that was not seen in girls. There was no evidence in this cohort for anaemia or vitamin A deficiency, but plasma zinc levels were reduced before treatment. Kimani Gachuhi (Kenya Medical Research Institute) also reported some nutritional aspects of the Kambu casecontrol study described earlier by Mwatha. In comparison with the controls, hepatosplenic patients showed Parasitology Today, vol. 14, no. 10, 1998

News reduced plasma levels of magnesium, calcium, zinc and vitamin A. Zinc levels were of interest in the context of immunoregulation; in the study group as a whole, plasma zinc correlated positively with IL-5 production in response to egg antigens, and negatively with IFN-g and TNF production. Gachuhi also presented data from a separate study in nearby Masongaleni, into which a large number of people had recently immigrated from an area not endemic for schistosomiasis, who could be compared with established residents in the same area. In the immigrant population shortly after they became infected, proliferative responses to worm antigens were lower, and responses to egg antigens higher, than in the comparable established population. The high SEA responses were associated with increased IL-10 production in the immigrant group, and this was possibly as a mechanism for downregulating the florid anti-egg responses that were demonstrable among the immigrants. Cynthia Naus (University of Cambridge, UK) described the antibody responses of the same populations, in whom different duration of exposure allows dissection of the influence of intensity of infection, duration of exposure, and age per se on different responses. For example, IgG4 responses against both worm and egg antigens were correlated with intensity of infection (especially as measured by CAA levels), whereas IgG1 responses against egg antigens were correlated with age, and were detectable in the immigrant children before they became detectably infected. IgG3 responses were stable with age, and were higher in the immigrants than in the established population, possibly reflecting simultaneous new exposure to malaria. Diana Karanja (Kenya Medical Research Institute) presented a study on car-washers from Kisumu in Kenya, with high intensities of S. mansoni infection and either infected or not infected with HIV, in whom egg excretion and praziquantel efficacy (both presumptively immune-dependent events) were compared. For a given level of circulating worm antigen, HIV-positive individuals excreted fewer eggs in their faeces than HIV-negative individuals, supporting the hypothesis that faecal egg excretion depends on an intact T-cell response. However, there was no difference in the efficacy of praziquantel between the HIV-positive and -negative groups, possibly because this depends on preformed antibodies rather than an intact T-cell system. Finally, in the context of possible influences of different Parasitology Today, vol. 14, no. 10, 1998

parasite isolates, Dirk Engels discussed the efficacy of praziquantel in the extensively studied outbreak of S. mansoni infection in the Senegal River basin. He presented evidence that favoured a multifactorial explanation for the observed poor efficacy of praziquantel, including high initial intensities of infection, the presence of immature worms at the time of treatment, a partially resistant local parasite isolate and, possibly, a relative lack in these recently infected individuals of a host antibody response acting synergistically with praziquantel. Control of Morbidity due to Schistosomiasis Studies on assessment and mechanisms of morbidity aim to contribute to improvements in control. John Ouma, among others, discussed optimization of control strategies in the context of age, treatment of women at puberty or after pregnancy, and selection of target populations. In the case of S. mansoni, in an area of initial low morbidity, treatment of schoolchildren at intervals of three years is sufficient for control, whereas in an area of high morbidity, annual treatment may be necessary. One problem about such protocols is that reinfection inevitably occurs, especially among children, and Curtis Kariuki (DVBD, Kenya) and Hilda Kadzo (Kenyatta National Hospital, Nairobi, Kenya) described a study in progress in the high morbidity Kambu area, whose aim was to follow regression of morbidity following a single treatment plus focal mollusciciding to abolish subsequent transmission. The Kambu River, the sole source of water for a population of some 40 000 individuals, was ideal for mollusciciding; Kariuki described a successful approach to controlling infected snails by twice-yearly drip-feeding of molluscicide downstream from the source of the river. Kadzo then gave preliminary ultrasonographic findings from a cohort of treated individuals that indicated a partial reduction in prevalence and severity of lesions at three and six months after initial treatment. Ouma had also highlighted the need for an integration of schistosomiasis control with other primary health care measures, and this theme was developed by Eric Muchiri (DVBD, Kenya) in the context of S. haematobium and intestinal nematode infections among schoolchildren in coastal Kenya. In each school, all children with detectable haematuria were treated annually with praziquantel, and all children, irrespective of nematode infection, were

treated two or three times a year with albendazole or levamisole, respectively. In the case of S. haematobium, morbidity as well as prevalence and intensity of infection were substantially reduced, even though only those with haematuria had been treated. Results for intestinal helminths were less beneficial: although Ascaris infections were reduced by treatment with either albendazole or levamisole, hookworm responded only to albendazole, while Trichuris showed a poor response to both drugs. A key aspect of the programme was the involvement of teachers in programme implementation, and a health education package was subsequently designed for use in primary schools. Robert Bergquist gave a detailed report of the TDR vaccine initiative, making the point that a vaccine would be useful not as a single control tool, but as part of a multifaceted and integrated approach. TDR has concentrated on six antigens of S. mansoni that have previously been found to be effective in animal models, and has coordinated independent confirmatory testing in mice and supported human field studies in Egypt, Brazil and Kenya investigating cellular and humoral responses to these antigens in groups of people treated and followed for one year post treatment. The mouse studies were disappointing, but in the human studies, all antigens studied elicited substantial responses of different types, and a decision has been taken to proceed with further vaccine testing in Egypt carried out by a new USAIDsupported project, the Schistosomiasis Vaccine Development Project (SVDP) in collaboration with the Egyptian Government, CDC and NIH in the US as well as the EU and TDR, with the aim of proceeding to Phase I and Phase II trials. Lester Chitsulo discussed the broader issue as to how research should be integrated into operational programmes of schistosomiasis control. The development of national control programmes, especially in sub-Saharan Africa, has been slow, and there is still a need in most countries to evaluate the extent to which schistosomiasis is a problem and the priority it should be accorded. Research programmes have a major role to play in defining the extent of the problem, in measuring the burden of disease, and in suggesting and testing new control strategies, as well as in communicating results and providing expertise and training in particular disciplines and skills. 389

News Acknowledgements The workshop, held in Nyeri, Kenya, 3–6 November 1997, was organized jointly by the Danish Bilharziasis Laboratory (DBL) and the Division of Vector Borne Diseases (DVBD) of the Kenyan Ministry of Health, and funded by DANIDA and the INCODC programme of the European Commission. It arose as a result of a previous DBL/DVBD workshop in Mombasa in 1995, and an EC meeting in Senegal in early 1997. It was attended by 41 participants from six

countries in Africa and nine in Europe or North America, who represented a network of collaborating research groups. The consensus was that much had been achieved since the last workshop two years earlier, and that such workshops had great value not only in the sharing of detailed scientific results but also in forging or strengthening collaborations between the various groups involved and discussion of future research needs. Participants at the workshop wished to record their appreci-

ation of the late Kenneth Mott’s contribution to the field of morbidity due to schistosomiasis. Birgitte Vennervald is at the Danish Bilharziasis Laboratory, Jaegersborg Allé 1D, DK-2920 Charlottenlund, Denmark. John Ouma is at the Division of Vector Borne Diseases, Nairobi, Kenya. Anthony Butterworth is at 47 The Footpath, Coton, Cambridge, UK CB3 7PX. Tel: +45 39 62 61 68, Fax: +45 39 62 61 21, e-mail: [email protected]

An International Initiative on Praziquantel Use E. Renganathan and D. Cioli Rome, Italy February 1998 Praziquantel is the drug of choice for the treatment of individual cases of schistosomiasis; it is also the main tool of most national and international schistosomiasis control programmes. As such, it has been administered to millions of people in endemic countries, in a variety of socio-economic, epidemiological and parasitological settings. Recent reports of low praziquantel efficacy have raised concerns about the possibility that drug-resistant schistosome strains may appear, with the danger of establishing themselves in endemic populations under selective pressure of continuous extensive praziquantel usage. Costs, Doses, Side Effects In spite of the obvious global dimension of the problems associated with praziquantel usage, the treatment has so far been planned, financed, administered and evaluated within the boundaries of individual endemic countries or, more often, just within the boundaries of single intervention programmes. Although there have been considerable reductions over the past few years, praziquantel cost is still a major problem in several countries. Prices ranging from 12.5¢ to $1 (and over) per tablet were reported at this first meeting of the EU-supported Concerted Action on Praziquantel. The panel decided to compile a list of current costs and to collect and disseminate information on the most convenient procurement procedures, in order to help extend drug 390

coverage to the largest possible number of patients (only a small fraction of whom are presently treated). The panel reviewed available information on schistosomiasis epidemiology (parasite species, prevalence etc.); the activities of national and international control programmes operating in the country; and specific praziquantelrelated information, such as usage in terms of standard dosages, availability of brands in the periphery and existence of locally produced drugs. The panel endorsed the recommended dosage of 40 mg kg21 body weight as generally effective against Schistosoma mansoni, S. haematobium and S. intercalatum. The usefulness of the praziquantel syrup formulation available in Egypt was noted. Side effects were generally considered mild enough to be acceptable in most situations; however, high-intensity foci provide one possible exception where special attention is necessary, since some serious problems (such as allergic reactions and bloody diarrhoea) have been reported. Developing Drug Resistance? A key topic of the meeting was a detailed analysis of available epidemiological evidence regarding the possible emergence of praziquantel-resistant schistosomes. The failure of chemotherapy is usually assessed on the basis of persistent egg excretion. The panel, therefore, felt it essential to collect data that could be as free as possible from interfering factors, such as reinfection after treatment, pre-existing immature

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parasites and the few residual schistosomes that survive even with a 99% effective drug. Similar interpretations have recently been entertained1 and might explain some of the field data without involving drug resistance. Other data, however, suggest the opposite interpretation, eg. the effectiveness of oxamniquine in a Senegalese focus where praziquantel had given poor cure rates, or the correlation of patient drug insensitivity with higher curative dose in laboratory animals in one Egyptian study. Taking advantage of the productive interaction of the diverse experiences of the participants, an innovative protocol was drafted, based essentially on the concept that two (or more) praziquantel treatments, given within a short interval and followed by an early egg count, might represent a simple yet effective procedure to eliminate many labour-consuming ‘false’ cases of drug resistance (see Fig. 1). Such a protocol would be adopted in selected areas where there is reason to suspect drug resistance (eg. if cure rates lower than 60% are observed). An additional advantage of double treatment in high-intensity areas would be the substantial elimination of the small percentage of worms normally surviving a single drug administration, since repeated treatments (assuming successive eliminations of 99% of parasites) would obviously reduce the load of surviving adult worms to negligible levels. The Concerted Action Initiative of the European Commission (INCO-DC Programme) took upon itself the task of refining such a protocol and of testing its feasibility and validity in the field. Parasitology Today, vol. 14, no. 10, 1998