Quantitative aspects of the epidemiology of Schistosoma japonicum infection in a rural community of Luzon, Philippines

Bulletin of the World Health Organization, SS (4): 629-638 (1980) Quantitative aspects of the epidemiology of Schistosoma japonicum infection in a rural community of Luzon, Philippines WHO WORKSHOP1 In a rural community on the island of Luzon, Philippines, the overall prevalence of Schistosoma japonicum infection, based on stool examination performed by both a new modified quantitative thick smear and the merthiolate-iodine-formaldehyde concentration (MIFC) technique, was 49.5% in a total study population of 755 persons. Peak prevalence was observed in the 15-19-year age group, then decreased gradually. Although the total egg output was highest in the 15-19-yearage group, individuals with high egg counts werefound among all age groups. Theprevalence and intensity ofinfection were higher in men than in women except in the 45-54-year age group. A small proportion (4.1I%) of the study population (age range 6-53 years) excreted 50% of the eggs counted in this study. Liver and spleen enlargement were significantly associated with S. japonicum infection in all age groups. Thefrequency of apast history ofdysentery and marked liver enlargement (., 5 cm) increased in parallel with increasing egg counts. Clustering of individuals with high egg counts in households was observed, but there was no correlation between geographical proximity of residence to potential transmission sites and household infection rates. An effective control strategy would be based on treatment ofall infectedpersons in this endemic area rather than only a selected age group. Epidemiological research on schistosomiasis, using quantitative methods in carefully defined popu- lations, has been recommended as a sound basis for developing and testing appropriate schistosomiasis control strategies (1). Schistosomiasis due to infection with Schistosoma japonicum is one of the major public health problems in eastern Asia, yet few quantitative epidemiological investigations have been reported (19). More than half a million Filipinos are estimated to be affected and 22 of the 58 provinces of the Republic of the Philippines are endemic areas (2). S.japonicum is also found in China, Japan, and in Central Sulawesi, Indonesia. In areas where S. mansoni infection is endemic, epidemiological research using quantitative tech- niques to determine egg output and clinical morbidity has contributed to the development of new control strategies, especially the effective use of oral chemo- therapy: this also applies to a lesser extent, to S. hae- I This article was written by the Editorial Committee of the WHO Workshop on Population Epidemiology of Schistosomajaponicum in the Philippines in 1978. The workshop was supported by the Scientific Working Group on Schistosomiasis, UNDP/World Bank/ WHO Special Programme for Research and Training in Tropical Diseases, and the WHO Regional Office for the Western Pacific. The participants in the workshop are listed in Annex 1, page 636. matobium infections (1). The promise ofeffective and safe chemotherapy for S.japonicum and the initiation of large internationally financed agricultural develop- ment programmes in Asia reinforce the importance of establishing quantitative techniques appropriate for epidemiological studies on S.japonicum. In the past, understanding of the epidemiology of S.japonicum has been limited by the lack of quantitative methods of stool examination whose sensitivity and reproducibility were acceptable under field conditions. A quantitative thick-smear technique has been successfully used in studies of S. mansoni (3) and has been adopted as the standard procedure for the Brazilian national control programme (4). This technique has since been used for S.japonicum (5) and in the present study has been modified for field use (see Annex 2, page 636). Several studies of the relationship between intensity of infection and morbidity in S. mansoni infection have been carried out (6-8), but similar investigations into S.japonicum infection have not previously been reported. Furthermore, the consensus of hospital- based observations has been that, although there are many similarities, S.japonicum infections cause more severe clinical gastrointestinal, hepatic, and central 3982 - 629 - 630 WHO WORKSHOP nervous system morbidity than is observed in S. mansoni infections (9). These observations have not previously been examined in a community-based epidemiological study. The epidemiological study reported here is the first to use a quantitative egg-counting technique and quantitative assessment of clinical morbidity based on standardized questionnaires and physical examin- ation. It had the following objectives: (i) to obtain quantitative data on the prevalence and morbidity of S.japonicum infection in two barangays (villages) on the island of Luzon, Philippines; (ii) to determine the epidemiological relationships between S.japonicum infection and morbidity, especially dysentery, hepatic and splenic enlargement, and central nervous system signs and symptoms; and (iii) to obtain demographic information necessary for future selective chemo- therapy campaigns and studies on other aspects of the epidemiology of schistosomiasis. MATERIALS AND METHODS Study area The study area covered the barangays of Bolos and Gumapia in Irosin, a municipality of Sorsogon Province, at the south-eastern part of the Bicol penin- sula of the island of Luzon, Philippines (Fig. 1). Irosin has an area of 158.5 km2 of flat terrain and is located at 12043' N, 1240 E. Irosin valley is of sandy loam to clay soil traversed by rivers and streams and bounded on the south, west, and east by mountains and on the north-east by Bulusan volcano. There is no distinct dry season. The average rainfall is 300-400 cm per year, the mean temperature is 27 °C, and the humidity is 85%. According to the 1977 census, the municipality of Irosin has a population of 30 989 ofwhom about 35%o reside in the poblacion, or town proper, and about 65%Mo live in the outlying barangays. The main source of livelihood is agriculture, rice farming being the principal occupation and economic activity. Other major crops are coconut, mainly as copra, and abaca, a fibre from native palms. The literacy rate is 80%7o, and 6007o of the school-age children attend school. According to the 1973-77 reports of the Sorsogon Provincial Health Office, the town had a crude birth rate of 47/1000 population, an infant mortality rate of 60/10 000 livebirths, and a crude death rate of 14/1000 population. Pulmonary tuberculosis, pneu- monia, bronchitis, and gastroenteritis are the main causes of morbidity and mortality. In addition to schistosomiasis, known endemic parasitic diseases are filariasis, paragonimiasis, and helminthiasis. Malaria is not endemic in Irosin. Based on a review of the records of the Schisto- somiasis Control and Research Service, the two barangays of Bolos and Gumapia were selected for study because of: (i) their high prevalence of schisto- somiasis; (ii) the negligible number of treated cases; (iii) the accessibility of both barangays; and (iv) their total population of 795 inhabitants. Methods In August 1978, detailed scale maps of the two barangays were prepared and the houses numbered. A complete household census was undertaken to obtain basic data on age, sex, family relation, birthplace, and years of residence. Information on occupation had been obtained during previous pilot studies. Snail colonies were identified by systematic searching of the study area and their locations were plotted on scale maps. One month after the census, labelled plastic cups for collection of faecal specimens were systematically distributed to all members of each household and left until the following morning. Each stool specimen obtained was examined in the field laboratory by both a cellophane thick-smear technique, modified by using methylene blue (glycerine solution and aqueous eosin),a and the merthiolate-iodine-formaldehyde concentration (MIFC) technique (10-12). One MIFC slide was prepared from each sample and read by two microscopists. Two thick-smear slides were also prepared and examined separately by two different microscopists who each read the slides twice, the first time horizontally and the second time vertically. Each slide was then checked once by another microscopist. The methodology and results of the analysis of intra- observer variation and sensitivity of the modified thick-smear method will be published elsewhere. The individual egg counts were obtained by multi- plying the mean of the two counts of S.japonicum eggs on each slide by 24 to give the number of eggs per gram. If one of the counts was zero, only the other count was considered. The geometric mean of the egg counts in age-specific groups was calculated by log transformation of the individual egg counts. The presence of other helminth ova was noted. The Hematesta method was used to determine the presence of occult blood in the stool. Morbidity questionnaires were prepared and indi- viduals of 10 years of age and older were questioned by interviewers fluent in the local dialect. Any occurrence of dysentery, convulsions, fever, dizziness, or head- ache during the previous four months was noted. The onset of menstruation and the intake of antischisto- somal medications were also determined. a See Annex 2, page 636. SCHISTOSOMIASIS IN THE PHILIPPINES 0 .0 '_ N 0%~~~~ t Do Fig. 1 Location map of the study area in the municipality of Irosin, Province of Sorsogon, Philippines. Physical examinations were performed on individ- uals of 5 years of age and older. The presence of super- ficial venous engorgement, the enlargement and consistency of the liver and spleen, and ascites were recorded. All the abdominal examinations were performed by two examiners with the subject relaxed in the supine position and the legs partially flexed. The findings were compared and the subject was re- examined in the event of discrepant results. Liver size was measured in centimetres below the right costal margin, by palpating the liver edge at the midclavicu- lar and midsternal lines, midway between inspiration and expiration. Similarly, spleen size was measured in centimetres below the left costal margin. The presence of peripheral oedema or neurological defect was re- corded. Height and weight were measured in all indi- viduals of 5 years of age and older. In persons over 15 years of age, blood pressure was determined on the right arm with the subject relaxed in a sitting position. In individuals with a history of convulsions or neuro- logical defects, sputum examination was performed to exclude paragonimiasis. The ages used in the analysis of the data were those recorded in the census of August 1978. Observations were entered on forms and the data was transferred directly to computer cards. Tabulations were performed on the IBM 368 of the Computer Centre of the University of the Philippines. 631 WHO WORKSHOP Table 1. Age and sex distribution of population, Irosin, Sorsogon, Philippines, August 1978 Bolos Gumapia Age group Total % (Years) Men Women Men Women <1 9 11 12 10 42 5.3 1-4 36 24 34 44 138 17.3 5-9 24 32 48 28 132 16.6 10-14 25 23 39 27 114 14.3 15-19 14 9 23 21 67 8.4 20-24 18 9 18 17 62 7.8 25-34 22 20 20 16 78 9.8 35-44 18 10 23 22 73 9.2 45-54 6 11 12 13 42 5.3 55-64 12 4 7 10 33 4.2 )65 2 4 6 2 14 1.8 Total 186 157 242 210 795 100.0 examination results were available, 580 were examined physically. Of 454 persons who were 10 years of age and older, 448 were interviewed. Of those examined, 42 persons (5.6%) reported that they had received stibophen or niridazole treatment in the past five years. The data from these treated individuals were analysed separately. Forty emigrants constituted the 5%70 who were not examined. The age and sex distri- bution of the study population is shown in Table 2. Prevalence The overall prevalence rate (49.5%) was based on the combined results from the modified thick-smear and MIFC techniques since the sensitivities of both methods were similar (P>0.05), as shown by the following comparative data: Positive Thick Negative smear TotalRESULTS MIFC Positive Negative 257 69 48 381 305 450 Total 326 429 755 Study population The demographic patterns and prevalence of S.japonicum infection in the two barangays were similar and they were therefore analysed as a single population (Table 1). More than 50% of the popu- lation were below 15 years of age. At the time of the census in August 1978, 795 persons were present in 127 households. In this study, 755 persons (95%o) were examined. Of 584 subjects who were 5 years of age or older and for whom stool In 48 individuals who were negative by the thick- smear but positive by the MIFC technique, the mean egg count was estimated to be 7 eggs per gram. The data presented here are based only on the results obtained by the modified thick-smear technique. No Paragonimus eggs were found in the stools by either MIFC or thick-smear examination. In this study, all the children examined below 1 year of age were found to be uninfected. The prevalence rate rose sharply to a peak of 70.2% in the 15-19-year age group after which it declined slightly and then Table 2. Prevalence and intensity of S.japonicum infection according to age and sex, Irosin, Sorsogon, Philippines Male Female Total Age group (Years) Number % Number % Number % examined Prevalence EPGa examined Prevalence EPGa examined Prevalence EPGa < 1 19 0 0 18 0 0 37 0 0 1-4 67 11.9 75 67 0 0 134 6.0 75 5-9 72 40.3 86 58 20.7 60 130 31.5 77 10-14 63 68.3 111 46 47.8 61 109 59.6 91 15-19 36 80.6 216 21 52.4 85 57 70.2 167 20-24 32 81.2 172 24 25.0 50 56 57.1 137 25-34 39 74.4 116 35 45.7 90 74 60.8 106 35-44 39 76.9 108 32 59.4 75 71 69.0 94 45-54 17 64.7 172 24 58.3 203 41 61.0 189 55-64 19 63.2 74 13 23.1 60 32 46.9 71 >65 8 62.5 90 6 16.7 92 14 42.9 91 Total 411 54.0 120 344 30.2 81 755 43.2 107 B Geometric mean egg count per gram of faeces based on the modified thick-smear method. 632 SCHISTOSOMIASIS IN THE PHILIPPINES reached another peak (69.0%) in the 35-44-year age group (Table 2). Thereafter, the prevalence rate gradually declined. As shown in Table 2, the overall prevalence rate in men (54.0%) was significantly higher than that in women (30.2%) (P<0.001). In men, the peak prevalence occurred in the 20-24-year age group whereas in women, it occurred in the 35-44-year age group. Intensity of infection In the age groups between 1 and 19 years, the inten- sity rose in parallel with prevalence. The peak intensity of infection in men occurred in the 15-19-year age group and in women in the 45-54-year age group (Table 2). The 15-19-year old age group (both sexes) registered the highest proportion of the total eggs counted in this population. By ranking the individual geometric mean egg counts (highest to lowest), it was observed that 4.1% (31 of 755) of the total study population, or 9.5% (31 of 326) of those infected, excreted 50% of the total eggs counted. Although 26.1 %o (12 of 46) of the men with counts of more than 400 eggs per gram were in the 15-19-year age group, 55.6% (5 of 9) of the women with similarly high egg counts were in the 45-54-year age group. Overall, 83.6%o (46 of 55) of individuals with high egg counts were males. Morbidity Questionnaire findings. A history of dysentery was significantly more frequent in individuals with egg counts of more than 400 eggs per gram (71.1 %, n = 45), than in individuals with lower egg counts (24.7%, n = 361: P<0.001). There was no significant correlation between the presence of infection and a history of convulsions, fever, other neurological defects, headache, or dizziness. There was no signifi- cant difference between the estimated median age (method of logits) of menarche in the infected women (15.8 years) and that in the non-infected group (15.3 years). (Normal test, Z = 0.45, P>0.05.) Physical examination. The overall prevalence of hepatomegaly (73.0%) was high in the study popu- lation and was significantly associated with S.japoni- cum infection (Cochran's test (13), 3.549 Z001 = 2.58) (Table 3). In all age groups, the prevalence of hepatomegaly was consistently higher in men than in women. Liver size of 5 cm and over was more com- mon in subjects with high egg counts (Table 4). The degree of bilobal liver enlargement was generally greater in the infected persons than in the non-infected individuals (Fig. 2). Splenomegaly was also significantly associated with S.japonicum infection (Cochran's test, 3.697 Z001 = 2.58). All the individuals with spleen enlargement also had liver enlargement. S.japonicum infection was not significantly corre- lated with ascites, peripheral oedema, superficial venous engorgement, presence of occult blood, or elevated blood pressure. Sputum examinations in nine individuals with neurological effects or history of con- vulsions were negative for Paragonimus eggs. The height and weight of both infected and non-infected individuals were consistently below Filipino standards (14). Table 3. Prevalence of hepatomegaly and splenomegaly according to S.japonicum infection by age and sex, Irosin, Sorsogon, Philippines Infected Non-infected Age group No. % with % with No % with % with examined hepatomegaly" splenomegalyb examined hepatomegalya splenomegalyb 5-9 41 92.7 12.2 89 87.6 6.7 10-14 59 89.8 25.4 38 81.6 5.3 15-19 37 67.6 8.1 15 46.7 13.3 20-24 31 67.7 9.7 24 37.5 8.3 25-34 38 68.4 18.4 25 52.0 4.0 35-44 45 73.3 11.1 20 65.0 5.0 45-54 21 90.5 19.0 14 28.6 0 55-64 12 50.0 8.3 16 56.2 0 >65 6 83.3 33.3 7 42.9 14.3 Total 290 77.9 15.5 248 67.3 6.0 a Liver edge palpable, >2 cm below right costal margin and/or the xiphoid at the midsternal line. b Spleen palpable below left costal margin or in the right lateral decubitus position. 633 WHO WORKSHOP Table 4. Intensity of infection (EPG) and liver size (cm) in individuals five years and older, Irosin, Sorsogon, Philippines 0-1 cm 2-4 cm No. % No. 81 38 19 5 2 32.7 23.9 23.8 14.3 12.5 145 27.0 50 15 12 6 1 20.2 9.4 15.0 17.1 6.2 >5 cm % No. % 117 106 49 24 13 47.2 66.7 61.2 68.6 81.2 84 15.6 309 57.4 n E z 60 50 40 30 20 10 Infected ---- Non-infected 1 2 3 4 5 Liver s Fig. 2 Distribution of individualk both the midclavicular and midsi Aggregation Clustering of individuals M present: 38.2% (21 of 55) of X resided in 20.9% (9 of 43) oi least one highly infected persc not due to an excess of residei high egg counts. Frequency sidered in relation to the proxi a snail colony. No statistically the frequency of infection those who lived within 50 m o lived further away. Previous chemotherapy Forty-two individuals of al received treatment for schistc five years and, of these, 31 (73.8%) were still excreting eggs, with faecal outputs ranging from 24 to 712 eggs per gram. Only 7 had undergone a complete course of treatment and 6 of these were still passing eggs. All 11 negative individuals had received treatment within the past two years. In the treated group, the presence of schistosomal infection was not significantly asso- ciated with a history of dysentery, hepatomegaly or splenomegaly. DISCUSSION A high prevalence of S.japonicum infection was observed in two barangays of Irosin, Sorsogon, an _--- __ _ E area known to be endemic since 1948 (15). An early 67 8 9 10 11 1'2 study on prevalence had recorded that only 5.66% of78 9 10 11 12 the population were infected (16). The prevalence ze (cm) among schoolchildren between 5 and 9 years of age in this study was similar to that reported in 1962 in with measurable livers at internal documents by the National Schistosomiasis ternal lines. Control and Research Service. Because of limited resources and the lack of anti- schistosomal drugs acceptable to the population, schistosomiasis control efforts in the Philippines have relied on environmental modification and intermit- nthhigh egg counts was tent snail control measures. The present study has f trhse hsouwseholdswiothat shown that, in spite of these interventions, the preva- Thouseholdsgawit wat lence of S.japonicum infection has not decreased overin. This aggregation was the last 30 years. Its from age groups with As in other epidemiological studies (5, 17) infection .ifetons co with S.japonicum was observed in the young age imity of the household to rsignificant difference in groups. The youngest infected person, a 1-year-oldboy, resided 10 m from a stream infested with was detectable btwseewho Oncomelania quadrasi. No female child under 5 years of age was infected. Casual observation suggests that this difference in the onset of infection in boys and girls may be attributed to earlier exposure among young boys, since they are allowed to play more freely. ge range 7-54 years had The prevalence and intensity of infection in males )somiasis within the past were significantly higher than in females. This Egg count (EPG) 0 1-100 101-400 401-800 >801 Total Total 248 159 60 35 16 538 u 634 SCHISTOSOMIASIS IN THE PHILIPPINES phenomenon has also been observed in Leyte (17) and in one village in Indonesia (5). The majority of snail colonies in the study area were found in canals and streams where men engage in freshwater fishing, an activity in which women rarely take part. Our data suggest that this occupation may be an important risk factor for reinfection, and that the rivers may be the most important transmission sites in this area. The high S.japonicum egg counts in older men and women were unexpected and difficult to explain in the absence of precise information on water-contact patterns for this population. Although Pesigan et al. (17) found a higher prevalence in the older females, no data on intensity was reported. In Indonesia (5), high prevalence and intensity of infection were noted in all age groups up to 55 years. As found in one S. mansoni endemic area (6), a small proportion (4.1%) of the study population excreted the majority of the total eggs counted; however, no single age group predominated among those individuals with high egg counts. Thus, although contamination of the environment is due to a small number of highly infected persons, chemo- therapy directed at a specific age group, as has been suggested in S. mansoni endemic areas (18), could not be expected to reduce significantly the total number of eggs excreted, or to have an impact upon morbidity related to high intensity infections. This study has confirmed that the frequency and degree of liver and spleen enlargement are associated with S.japonicum infection per se in this endemic area. In addition, the frequency of both a history of dysentery and marked liver enlargement () 5 cm) in- creased in parallel with the intensity of infection. Previously, the role of schistosomiasis in the high prevalence of liver enlargement, in relation to other possible etiologies such as viral infection or malnu- trition in rural populations in the Philippines has been questioned (15). Other signs and symptoms, including central nervous system involvement, have been reported to be associated with S.japonicum infection. However, no significant correlation was found in this small popu- lation. Since the study area was endemic for Paragon- imus, that infection was first ruled out in the differ- ential diagnosis of any central nervous system disease. Household clustering of individuals with high egg counts was observed. However, high household prevalence was not correlated with proximity to known snail colonies. Our data indicate that certain water contact habits within certain families, rather than the proximity of their residence to probable transmission sites, may be responsible for the in- creased occurrence of infection. Stool examination using the modified thick-smear method was performed easily under field conditions and the sensitivity of the technique is improved by repeated examinations. The MIFC method was a more laborious procedure and its limitations as a quanti- tative method have been described previously (12). The modified thick-smear technique is therefore recommended as a practical quantitative stool exam- ination method for epidemiological studies on S.japonicum. The high prevalence of infection among the subjects who had received specific treatment in the past suggests that therapy had been incomplete or ineffec- tive, or, more likely, that there had been repeated exposure and reinfection. Stibophen and niridazole had previously been used in the treatment of schistosomiasis in Irosin and both require a prolonged course which many subjects did not complete. Since the overall prevalence has remained unchanged or perhaps even increased in the past 30 years, the high prevalence in the treated group was anticipated. The age- and sex-specific prevalence rates of S.japonicum infection in Leyte have been shown to be markedly different in the poblacion (urban areas), the coastal, and inland regions (17). The present study area, which was located in Luzon, is similar in geography and ecology to the inland area of Leyte. Differences in the age- and sex-specific distribution of prevalence and intensity within communities of dif- ferent endemic areas may be anticipated, but their significance can be recognized only through epidemio- logical studies using quantitative methods. Improved schistosomiasis control methods and the recent availability of new antischistosomal drugs now require further standardized quantitative epidemio- logical studies in well-defined communities, in order to develop appropriate control strategies and to evaluate their effectiveness. 635 636 WHO WORKSHOP Annex I PARTICIPANTS Roger F. Abear, Roque A. Burio, Felix A. Gillego, Marcela C. Papasin, Raoul C. Villarete, The Schistosomiasis Control and Research Service Ministry of Health, Philippines Zacarias C. Frivaldo, the Municipal Health Office of Irosin, Ministry of Health, Philippines Caridad A. Ancheta, Angelita C. Camacho, Nonette L. Jueco, the Institute of Public Health, University of the Philippines System Edita D. Tiu, Cynthia I. Valencia, the College of Medicine, University of the Philippines System Consultants Arturo C. Reyes, Institute of Public Health, Univer- sity of the Philippines System (Coordinator) Idelfonso T. Cruz, Professor of Biostatistics and Epidemiology, Institute of Public Health, Univer- sity of the Philippines System Edito G. Garcia, Professor of Parasitology, Institute of Public Health, University of the Philippines System Kenneth E. Mott, UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, World Health Organization, Geneva, Switzerland Annex 2 LABORATORY PROCEDURES Modified thick smear method:' A plastic template with one hole is placed on a slide and approximately 41.7 mg of faeces are levelled on top so as to fill the hole. The template is then removed to leave the specimen on the slide. The faeces are covered with a 3.5 cm x 2.5 cm cellophane film, previously soaked for 24 hours in a solution consisting of0.3 ml of satur- ated solution of methylene blue in sodium acetate buffer (pH 3.8), diluted to 100 ml with 25% glycerine. The slide is turned upside down, pressed against a flat surface to form a uniform thick smear and allowed to clear for 15-30 minutes. About 3-5 drops of 1%7 aqueous eosin solution prepared from a saturated aqueous eosin solution are added gently over the cello- phane square, left for 2-4 minutes then wiped with absorbent paper. The S.japonicum eggs, as well as other helminth eggs, are then readily seen. The number of eggs counted is multiplied by 24 to give the number of eggs per gram. The Hematestb method consists of smearing faeces thinly on a filter paper. The tablet contained in the kit is placed at the centre of the smear. One drop of water is added on top of the tablet. After 5-10 seconds another drop is added to its side. Blue colour on the filter paper within 2 min indicates the presence ol occult blood. RESUMt ASPECTS QUANTITATIFS DE L'EPIDEMIOLOGIE DE LUINFECTION A SCHISTOSOMA JAPONICUM DANS UNE COLLECTIVITE RURALE DE LU4ON (PHILIPPINES) Cette etude epidemiologique quantitative a e entreprise dans une collectivite rurale de I'lle de Lucon (Philippines) en vue de: i) obtenir des donnees quantitatives sur la prevalence de l'infection a S.japonicum et de la morbidite qui lui est liee; ii) determiner la relation epidemiologique entre l'intensite de l'infection et la morbidite; et iii) obtenir les a Kit A-K, A-K Industria e Comercio Ltda., Belo Horizonte, Minas Gerais, Brazil. renseignements demographiques necessaires pour de futures campagnes de chimiotherapie selective parmi la population. Dans la zone etudiee, des cartes detaillees, l'identification des maisons par numerotage et le recensement des menages ont e realises. Des echantillons de selles ont e examines au laboratoire sur le terrain par une methode quantitative b Ames Co., Division of Miles Laboratories, Elkhart, Indiana, USA. SCHISTOSOMIASIS IN THE PHILIPPINES 637 modifiee de frottis epais et par la methode de concentration au merthiolate-iode-formaldehyde (MIF). La morbidite a e determinee au moyen d'un questionnaire dans le dialecte local et par un examen physique. Sur les 755 habitants, 95% ont fourni des echantillons de selles. Les donnees relatives A 42 personnes qui ont signale avoir anterieurement recu un traitement specifique contre la schistosomiase ont e analys&es separement. La prevalence globale, fondee sur les resultats combines des deux diffe- rentes methodes d'examen coprologique, etait de 49,5%. La prevalence globale etait maximale dans le groupe d'age 15-19 ans. Cependant, chez les hommes, le maximum se situait dans le groupe d'age 20-24 ans et chez les femmes, dans le groupe d'age 35-44 ans. La prevalence etait nette- ment plus elev&e chez les hommes (54,0%) que chez les femmes (30,2%). L'intensite de l'infection etait maximale dans le groupe d'Age 15-19 ans. Dans la population etudiee, 4,1% des sujets (Ages de 6 A 53 ans) excretaient 50% des ceufs denombres. Parmi les sujets chez qui l'on a compte 400 ceufs ou plus par gramme, 83,6% etaient de sexe masculin. La plupart des femmes chez qui la numeration d'aeufs donnait des resultats eleves avaient 40 A 54 ans. La frequence des antecedents de dysenterie etait signifi- cativement plus elevee chez les sujets ayant un nombre eleve d'oeufs que chez ceux dont la numeration d'oeufs donnait des resultats faibles ou nuls. II n'y avait pas de correlation significative entre la presence de l'infection et des antece- dents de convulsions, fievre, cephalee et vertiges ou debut precoce de la menstruation. L'hypertrophie du foie et la splenomegalie, presentaient une association significative avec l'infection A S.japonicum, et leur frequence etait plus grande chez les hommes infectes que chez les femmes infectees. La frequence de l'hepato- megalie (5 cm ou plus) augmentait, parallelement, avec les ceufs denombres. La frequence et le degre de l'hypertrophie bilobaire du foie etaient superieurs chez les personnes infectees que chez les sujets non infectes. II n'y avait pas de correlation significative entre l'infection a S.japonicum et d'autres signes ou sympt8mes physiques. Une infection intercurrente a Paragonimus a e exclue par examen des expectorations chez toutes les personnes ayant des antecedents de convulsions ou de troubles neuro- logiques. On a constate un groupement de sujets ayant des numera- tions d'ceufs elev&es dans certains menages, mais il n'y avait pas de correlation avec la proximite geographique du lieu d'habitation par rapport aux lieux de transmission potentiels. Parmi les personnes qui ont signale un traitement anterieur, 73,8% excretaient des ceufs, mais leurs numera- tions se situaient au bas de l'echelle. Dans ce groupe, tous les sujets negatifs avaient e traites au cours des deux dernieres annees; d'autre part, il n'a pas e observe de correlation entre l'infection et la morbidite. Comme dans les etudes effectu&s dans d'autres zones d'endemie, la prevalence elevee de l'infection, surtout dans le sexe masculin, peut etre en rapport avec une exposition professionnelle. Du fait que les sujets presentant des numerations d'oeufs elevees ne predominaient dans aucun groupe d'age determine, la chimiotherapie s'adressant a un groupe d'age particulier ne semblait pas devoir reduire considerablement le total des ceufs excretes dans cette population. La necessite de methodes quantitatives pour des etudes epidemiologiques dans d'autres zones d'endemie est soulignee. REFERENCES 1. SCIENTIFIC WORKING GROUP ON SCHISTOSOMIASIS. 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