Differentiation between Bulinus truncatus and Bulinus hexaploidus by morphological characters, chromosomal study and compatibility with Schistosoma haematobium.

Schistosomiasis is a snail-born, neglected tropical disease (NTD) caused by blood flukes (trematode worms) of the genusSchistosoma. It is the second most socioeconomically devastating parasitic disease after malaria. Urogenital schistosomiasis is caused by Schistosoma haematobium which is transmitted by snail intermediate host of the genus Bulinus. This genus is a model system for the study of polyploidy in animals. This study aims to investigate ploidy levels existing among the Bulinus species and their compatibility with S. haematobium. The specimens were collected from two governorates in Egypt. Chromosomal preparation was made from gonad tissue (ovotestis). This study found two ploidy levels (tetraploid, n = 36 and hexaploid, n = 54) of B. truncatus/tropicus complex in Egypt. Tetraploid B. truncatus was found in El-Beheira governorate while-unexpectedly and for the first time in Egypt, the hexaploid population was found in Giza governorate. This identification focused on shell morphology, chromosomal count, and spermatozoa of each species. Afterward, all species were exposed to S. haematobium miracidia where B. hexaploidus snails were the only refractory species. The histopathological study showed early destruction and abnormal development of S. haematobium in B. hexaploidus tissues. In addition, the hematological investigation showed increasing in the total hemocyte count, the formation of vacuoles, several pseudopodia, and more dense granules in the hemocytes of infected B. hexaploidus snails. In conclusion, there were two types of snails one was refractory and the other was susceptible.

Nuclear genome of Bulinus truncatus, an intermediate host of the carcinogenic human blood fluke Schistosoma haematobium.

Some snails act as intermediate hosts (vectors) for parasitic flatworms (flukes) that cause neglected tropical diseases, such as schistosomiases. Schistosoma haematobium is a blood fluke that causes urogenital schistosomiasis and induces bladder cancer and increased risk of HIV infection. Understanding the molecular biology of the snail and its relationship with the parasite could guide development of an intervention approach that interrupts transmission. Here, we define the genome for a key intermediate host of S. haematobium-called Bulinus truncatus-and explore protein groups inferred to play an integral role in the snail's biology and its relationship with the schistosome parasite. Bu. truncatus shared many orthologous protein groups with Biomphalaria glabrata-the key snail vector for S. mansoni which causes hepatointestinal schistosomiasis in people. Conspicuous were expansions in signalling and membrane trafficking proteins, peptidases and their inhibitors as well as gene families linked to immune response regulation, such as a large repertoire of lectin-like molecules. This work provides a sound basis for further studies of snail-parasite interactions in the search for targets to block schistosomiasis transmission.

Characteristics of persistent hotspots of Schistosoma mansoni in western Côte d'Ivoire.

BACKGROUND: Preventive chemotherapy with praziquantel is the cornerstone of schistosomiasis control. However, in some social-ecological settings, the prevalence and/or intensity of Schistosoma infection does not lower meaningfully despite multiple rounds of preventive chemotherapy, a phenomenon termed persistent hotspot (PHS). We assessed the characteristics of PHS in a Schistosoma mansoni-endemic area of Côte d'Ivoire. METHODS: In October 2016, a cross-sectional survey was conducted in 14 schools in the western part of Côte d'Ivoire, one year after multiple rounds of preventive chemotherapy. In each school, 50 children aged 9-12 years provided two stool samples and one urine sample. Stool samples were subjected to triplicate Kato-Katz thick smears for S. mansoni diagnosis. Urine samples were examined by a filtration method for S. haematobium eggs. PHS was defined as failure to achieve a reduction in the prevalence of S. mansoni infection of at least 35% and/or a reduction of infection intensity of at least 50%. Six schools underwent more detailed investigations, including a questionnaire survey for demographic characteristics and a malacological survey. RESULTS: In the six schools subjected to detailed investigations, the overall prevalence of S. mansoni and S. haematobium was 9.5% and 2.6%, respectively. Four schools were classified as PHS. The S. mansoni prevalence in the four PHS was 10.9% compared to 6.6% in the remaining two schools. The S. mansoni infection intensity, expressed as arithmetic mean eggs per gram of stool (EPG) among infected children, was 123.8 EPG in PHS and 18.7 EPG in the other two schools. Children bathing in open freshwater bodies were at higher odds of S. mansoni infection (odds ratio: 4.5, 95% confidence interval: 1.6-12.6). A total of 76 human-water contact sites (53 in PHS and 23 in the other schools) were examined and 688 snails were collected, including potential intermediate host snails of Schistosoma (Biomphalaria pfeifferi, Bulinus forskalii, Bu. globosus and Bu. truncatus). CONCLUSION: Children in PHS schools bathed more frequently in open freshwater bodies, and hence, they are more exposed to Schistosoma transmission. Our findings call for an integrated control approach, complementing preventive chemotherapy with other interventions, particularly in PHS settings.

Schistosomiasis Control in Nigeria: Moving Round the Circle?

Background: Schistosomiasis has continued to plague low-resource areas of the Nigerian population. Mass drug administration (MDA) has been the only adopted interventional program for decades. However, it appears this effort does not culminate in transmission and morbidity reduction. Purpose: To highlight the current situation of schistosomiasis in Nigeria, why MDA alone cannot achieve the expected result, identify research needs, and promotion of integrated control approach for schistosomiasis. Method: A viewpoint based on practices, research findings, and personal and professional experience in the field of schistosomiasis control. Conclusion: This viewpoint strongly advocates a commitment to the integrated control approach through the development of robust schistosomiasis control policy for the country. It stressed the need for research priorities in neglected areas of schistosomiasis that are germane for control of the disease. The government's willpower to implement important recommendations from research outcomes is important to achieve success.

Urinary schistosomiasis in Nigeria: a 50 year review of prevalence, distribution and disease burden.

We reviewed survey data deposited in the Global Neglected Tropical Diseases database and many other articles on the prevalence and distribution of Schistosoma haematobium in Nigeria. Schistosoma haematobium surveys conducted over the period of 50 years under review using different diagnostic tools revealed that Ogun State has the highest prevalence, followed by Ekiti state, while the lowest prevalence was recorded in Adamawa. No incidence of Schistosoma haematobium was recorded for states such as Akwa Ibom, Bayelsa, Nasarawa, Jigawa and Gombe. In terms of endemicity, this review has shown that Nigeria is divided into four zones: hyperendemic, moderately endemic, low endemic, and no endemic zones. A survey of 47 (15%) of the 323 dams in Nigeria revealed that 45 out of the 47 dams are located in the hyperendemic zone, while the remaining two are located in the moderately endemic zone. Twenty (43%) of the total surveyed dams harboured Bulinus globosus and/or Biomphalaria pfeifferi, the local intermediate hosts of schistosomes, and 18 of these are located in the hyperendemic zone, while the other two are in the moderately endemic zone. We conclude that there is an urgent need to carry out a nationwide survey to help in planning, coordinating, and evaluating schistosomiasis control activities.

Prevalence and seasonal transmission of Schistosoma haematobium infection among school-aged children in Kaedi town, southern Mauritania.

BACKGROUND: Mauritania is at the fringe of transmission of human schistosomiasis, which mainly occurs in the southern and southeastern parts of the country. This study aimed to assess the influence of rainfall seasonality on the prevalence of Schistosoma haematobium infection among school-aged children in Kaedi, southern Mauritania. METHODS: Cross-sectional surveys (i.e. parasitological, malacological and observations on water-related human activities) were carried out in Kaedi between September 2014 and May 2015, during both the wet and dry seasons. A total of 2162 children aged 5-15 years provided a single urine sample that was subjected to S. haematobium diagnosis. Snails were sampled and checked for cercarial shedding. Water contact patterns of the local population were recorded by direct observation. RESULTS: The prevalence of S. haematobium was 4.0% (86/2162, 95% confidence interval (CI): 3.2-4.9%) with a geometric mean egg count per 10 ml of urine of 3.7 (95% CI: 2.8-4.3). Being male (adjusted odds ratio (aOR) 1.78, 95% CI: 1.13-2.80), being at primary school (aOR 1.73, 95% CI: 1.04-2.87) and dry season (aOR 0.56, 95% CI: 0.35-0.89) were significantly associated with S. haematobium. Among 284 potential intermediate host snail specimens collected over the rainy and dry seasons, three species were identified: Bulinus senegalensis (n = 13) and B. forskalii (n = 161) in the rainy season, and B. truncatus (n = 157) in the wet season. No snail was shedding cercariae. On average, seven human water contacts were recorded per hour per observer over a 28-day observation period. Twelve types of water contact activities were identified among which, swimming/bathing was predominant (n = 3788, 36.9%), followed by washing clothes (n = 2016, 19.7%) and washing dishes (n = 1322, 12.9%). Females (n = 5270, 51.4%) were slightly more in contact with water than males (n = 4983, 48.6%). The average time spent in the water per person per day was 14.2 min (95% CI: 13.8-14.6 min). The frequency and duration of water contact followed a seasonal pattern. CONCLUSION: Our findings demonstrate a low prevalence and intensity of S. haematobium among school-aged children in Kaedi. Appropriate integrated control measures, including health education among at-risk communities and snail control may help to interrupt transmission of S. haematobium in Kaedi.

Efficacy of praziquantel and reinfection patterns in single and mixed infection foci for intestinal and urogenital schistosomiasis in Cameroon.

The regular administration of the anthelminthic drug praziquantel (PZQ) to school-aged children (and other high-risk groups) is the cornerstone of schistosomiasis control. Whilst the performance of PZQ against single schistosome species infections is well-known, performance against mixed species infections is less so, as are patterns of re-infection following treatment. To address this, a study using a double treatment with PZQ, administered at 40 mg/kg spaced by 3 weeks, took place in two mixed intestinal-urogenital schistosomiasis foci in northern Cameroon (Bessoum and Ouro-Doukoudje) and in one single intestinal schistosomiasis infection focus (Makenene). A total of just under 1000 children were examined and the Schistosoma-infected children were re-examined at several parasitological follow-ups over a 1-year period posttreatment. Overall cure rates against Schistosoma spp. in the three settings were good, 83.3% (95% confidence interval (CI)=77.9-87.7%) in Bessoum, 89.0% (95% CI=79.1-94.6%) in Ouro Doukoudje, and 95.3% (95% CI=89.5-98.0%) in Makenene. Interestingly, no case of mixed schistosome infection was found after treatment. Cure rates for S. mansoni varied from 99.5% to 100%, while that for S. haematobium were considerably lower, varying from 82.7% to 88.0%. Across transmission settings, patterns of re-infection for each schistosome species were different such that generalizations across foci were difficult. For example, at the 6-month follow-up, re-infection rates were higher for S. haematobium than for S. mansoni with re-infection rates for S. haematobium varying from 9.5% to 66.7%, while for S. mansoni, lower rates were observed, ranging between nil and 24.5%. At the 12-month follow-up, re-infection rates varied from 9.1% to 66.7% for S. haematobium and from nil to 27.6% for S. mansoni. Alongside these parasitological studies, concurrent malacological surveys took place to monitor the presence of intermediate host snails of schistosomiasis. In the two northern settings, three species of Bulinus (intermediate host snail of S. haematobium) were collected; i.e. Bulinus truncatus, B. globosus and B. senegalensis, however, Biomphalaria pfeifferi (intermediate host snail of S. mansoni) was much rarer despite repeated and intensive searching and was suggestive of limited local transmission potential of S. mansoni during this time. While this study highlights that performance of PZQ was satisfactory in this region, with somewhat greater impact upon intestinal than urogenital schistosomiasis, the dynamics of local transmission are shown, however, to be complex.

Further assessment of Mirazid as antischistosomal drug in experimental schistosomiasis hematobium.

Conflicting reports are found in the literature about the efficacy of Mirazid (MZ), which is a special formulation of myrrh obtained from the stem of Commiphora molmol (Nees), Engl. tree (Burseraceae), as an antischistosomal drug. This initiated the present study to further assess this drug in experimental schistosomiasis hematobium. The drug was administered orally to hamsters infected with Schistosoma hematobium ( Bilharz, 1852 ) using 500 mg/kg body weight for six successive days on an empty stomach. The drug effect was examined after three periods: 4, 8 and 12 weeks post-treatment. Emphasis was given to certain parameters such as change in worm load, number of ova/mg tissue, oogram pattern and number of ova/g stool, and tegumental changes in the worms by electron microscopy after prolonged observation periods. The results showed very slight 3.4% worm reduction by MZ after the longest evaluation period (12 weeks), versus very high reduction (100%) by the reference drug praziquantel (PZQ). In comparison with the untreated control no change was found in the number of ova/mg tissue in MZ-treated hamsters regardless of the date of observation (4-12 weeks), versus significantly high reduction (99.6%) observed in the case of PZQ treatment. However, a significant decrease (22%) in the ratio of immature and increase in dead ova in tissues of MZ-treated hamsters was obvious at 12 weeks post treatment. In MZ-treated animals, a slight reduction (18.3%) in the number of stool eggs versus absence of eggs in PZQ-treated animals 12 weeks after treatment. Scanning electron microscopic examination of S. hematobium worms revealed intact tubercles, spines and sensory bulbs and no effect of the ventral side after MZ treatment. Meanwhile, PZQ treatment revealed extensive disruption of the tegument worm. Therefore, this experimental study gives extra support to previously reported negative evaluation about the effectiveness of this drug in the treatment of schistosomiasis against many other published positive results. This controversy about the efficacy of MZ may be attributed to inconsistency of its material which is obtained from natural origin.

Field trials of low dose Bayluscide on snail hosts of schistosome and selected non-target organisms in sahelian Cameroon

More than 85 percent of all cases of schistosomiasis in Cameroon occur in the northern sahelian half of the country representing 20 percent of the population. Several workers have advocated the integrated approach to schistosomiasis control, including snail control, but the death and decay of aquatic organisms, and fish kill that often follows Bayluscide application at the dose of 1g/m³ decrease its acceptability. The present study was designed to assess the effect of lower Bayluscide doses on snail host and non-target fish, frog, the tadpole kill. Bayluscide was applied to study ponds at concentrations of 0, 0.25, 0.5, and 1 g/m³ (ppm). Pre and post application assessment of snails hosts of schistosomes, fish, frog, and tadpole kill were carried out. All 0.25, 0.5, and 1 g/m³ Bayluscide concentrations reduced snail population significantly. Bayluscide concentration of 0.50 g/m³ applied in two rounds of 0.25 g/m³ resulted in high snail mortality and low lethality to fish, frogs, and tadpoles. Further studies are needed to assess the cost-effectiveness of Bayluscide in the control of schistosomiasis following the simplified approach.

[Heterogeneity of Schistosoma haematobium transmission in irrigated fields]. / Hétérogénéité de la transmission de Schistosoma haematobium dans les périmètres irrigués du Niger.

Heterogeneity of Schistosoma haematobium transmission in irrigated fields. Although irrigated areas exist since a long time in the Niger Valley the distribution of the urinary schistosomiasis does not appear homogeneous, testifying to the existence of limiting or favourable factors. The identification of these factors could lead to a better definition of the distribution of the schistosomiasis risks and to optimise control programmes. The population of five villages about 1,900 inhabitants living in the same irrigated area (Sébéri) was examined at the end of 1999 before treatment and surveyed two and ten months after treatment by praziquantel in order to investigate re-infections. In parallel, the transmission sites were subject to a semi-monthly malacological follow-up from 1998 to 2001 and the water contacts were quantified in the sites of the main village during 2000. Before treatment, schistosomiasis risks appeared related to the proximity between habitat and lateral canals: the infections concerning youngers were all the more intense that the dwellings were close to the canal. The parasitological indices were the highest in the village lacking of other water sources. The morbidity indices followed a similar distribution with maximum values in the children of the 3 villages located to less than 1 km from the canal; however, morbidity was mainly observed in the adult population, in particular male, of the 2 villages which were the most distant from the canal. After treatment, the incidence of the re-infection between 2 and 10 months was comparable in the 3 villages close to the canal (28%) but was significantly weaker in the 2 villages far from the transmission sites (5%). In the villages bordering the canal, the incidence in the children was all the more high since the habitat was close to the canal. Between 1999 and 2000, the collected number of Bulinus truncatus decreased from 1.4 to 0.6 individuals per survey; moreover, no mollusc harbouring parasites was found, representing the decrease of the parasite burden. The abnormal weakness of re-infection, regarding this type of focus, could be explained by the repeated stop of water supply inducing a complete drying out of the canal for 2 months during the year preceding the study. These repeated drying out also resulted in a reduction of the exposure. Whereas the average frequentation of the sites of the canal remained rather comparable between January (cold dry season) and May (dry hot season), it decreased dramatically in September (rainy season but canals were not irrigated this year) from 99 to 11 daily contacts. The use of the lateral canal when filled represented 80% of the contacts. In the event of drying out, 80% of the contacts were transferred in the ponds but not in the river (5% of the contacts whatever the season). These results confirmed (1) that the presence of canals reduced the use of natural sites and (2) that the drying out of the canals induced a total reduction of the contacts.

Studies on the biology of schistosomiasis with emphasis on the Senegal river basin

The construction of the Diama dam on the Senegal river, the Manantali dam on the Bafing river, Mali and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni in Northern Senegal, associated with high intensity of infections, due to intense transmission, and the creation of new foci of S. haematobium. Data on the vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard Toll, Senegal are presented with sympatric and allopatric (Cameroon) S. mansoni. Comparisons are made on infectivity, cercarial production, chronobiology of cercarial emergence and longevity of infected snails. Recent data on the intermediate host specificity of different isolates of S. haematobium from the Lower and Middle Valley of the Senegal river basin (SRB) demonstrate the existence of at least two strains of S. haematobium. The role of Bulinus truncatus in the transmission of S. haematobium in the Lower and Middle Valleys of the SRB is reviewed. Both S. haematobium and S. mansoni are transmitted in the same foci in some areas of the SRB

The effects of irrigated agriculture on the transmission of urinary schistosomiasis in the Middle and Upper Valleys of the Senegal River basin.

The importance of the increase in irrigated land on the perimeters of the Middle and Upper Valleys of the Senegal River basin, on the prevalence and intensity of urinary schistosomiasis, was investigated. Surveys were conducted, in May-June 1997, to determine the prevalence and intensity of Schistosoma haematobium infection among 1445 children aged 7-14 years: 1011 in 10 villages near Matam, and 434 in four villages near Bakel. Macrohaematuria was present in seven of the study villages (four near Matan and three near Bakel), whereas microhaematuria was present in all the villages, with prevalences of 10%-73%. A second survey, conducted, in June 1999, on 755 children from nine of the study villages near Matam, demonstrated significant increases in the prevalences of both micro- and macro-haematuria in three of the villages, all of which were adjacent to the Senegal River and practising irrigated agriculture. None of the other study villages re-surveyed was irrigating any of its agricultural land. A longitudinal survey was also carried out, between May 1997 and November 1998, on about 10% of the population (2272 subjects) of Nguidjilone, north of Matam; selective treatment with praziquantel (40 mg/kg) was given in May 1997, and mass treatment in May 1998. The data analysed were those relating to the 125 individuals who provided samples at each survey. Very severe infections (> 1000 eggs/10 ml urine) were seen in five subjects in May 1997. One year later (i.e. 1 year after the selective treatment), the prevalence of urinary schistosomiasis had increased in every age-group. Although prevalence had decreased slightly by November 1998 (6 months after the mass treatment), the intensity of the infections seen had increased in every age-group. At the end of the dry season (May-June 1997), Bulinus truncalus infected with schistosome cercariae were recovered from the Senegal River. However, immediately after the next rainy season (November 1997), no snails were found at any collection site on the river.

Susceptibility of Ethiopian bulinid snails to Schistosoma haematobium from Somalia.

Susceptibility of four Ethiopian bulinid snails to a Somalian strain of S. haematobium was tested. Bulinus abyssinicus was highly susceptible and lowland B. africanus was partially susceptible while B. truncatus and B. forskalii were refractory to the parasite. It is suggested that Ethiopian refugees returning from Somalia and/or Somalian refugees entering Ethiopia should be screened and treated for S. haematobium before they are allowed to work/resettle in development areas where B. abyssinicus and B. africanus are known or ecologically suspected to occur.

Age-acquired resistance and predisposition to reinfection with Schistosoma haematobium after treatment with praziquantel in Mali.

The effect of age, previous intensity of infection, and exposure on reinfection with Schistosoma haematobium after treatment was studied in a cohort of 468 subjects six years of age and over living in an irrigation scheme area in Mali. Prevalence and intensity of S. haematobium infection were measured each year between 1989 and 1991, but the reinfection study period was restricted to the last year of the follow-up. Observations were made at the principal water contact sites where the number of Bulinus truncatus shedding furcocercous cercariae was recorded. A cumulative index of exposure taking into account time, duration and type of contact, and malacologic data was calculated for each subject. Univariate analysis showed that the reinfection risk decreased with age and increased with exposure and pretreatment intensity. These results were confirmed by fitting a logistic model that showed that this risk was seven times lower among those 15 years of age and older than among the 6-14-year-old children, while linear trends with exposure to infection and pretreatment intensity were significant. This study supports the concept of an age-acquired resistance to reinfection and is in favor of a predisposition to infection that raises the question of a genetic factor controlling susceptibility/resistance to S. haematobium infection.

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

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

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

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

Schistosoma haematobium infection among Ethiopian prisoners of war (1977-1988) returning from Somalia.

Fifty Ethiopian male prisoners of war aged 20-34 years returning from Somalia were examined at the Schistosomiasis Diagnostic Laboratory of the Institute of Pathobiology, Addis Abeba University, Addis Abeba in 1988. Medical history was obtained and their urine was examined by the filtration technique. Recovered eggs of S. haematobium were allowed to hatch as a test for viability. Positive patients were treated with praziquantel at a single dose of 40mg per kg. 94% of the prisoners gave history of haematuria and 96% gave history of treatment for schistosomiasis while in Somalia. S. haematobium egg positivity rate was 30% and all but one patient had viable eggs in their urine. The geometric mean egg count per 10ml urine was only 6.4. Urine examination of treated cases six weeks later showed 100% cure rate. A preliminary compatibility study between Ethiopian Bulinus snails and the Somalian strain of S. haematobium showed that B. abyssinicus and B. truncatus were susceptible to the parasite while B. africanus was only partially susceptible. The possibility that a foreign strain of S. haematobium may be introduced into ecologically and malacologically receptive areas in Ethiopia is discussed.

Foci of Schistosoma mansoni in Assiut province in middle Egypt.

Following detection of Schistosoma mansoni in a 12 years old boy who had both schistosomal polyposis and periportal fibrosis with hepatosplenomegaly, epidemiological studies to confirm local transmission were performed in his and 30 other villages in Assiut Governorate, Egypt. The index case's brother and 6 of 380 inhabitants of his village who provided stool specimens were infected with S. mansoni and a farmer with dysentery and hepatosplenomegaly had a positive rectal snip biopsy. All had hepatic abnormalities on ultrasound examination. Two of 221 schoolchildren in another village had mixed infections with S. mansoni and S. haematobium; 17 others had only S. haematobium. None of 419 inhabitants living near the infected boys had S. mansoni infection. Snails from canals and drains near both villages were netted, identified, counted and checked for infection: in the second village one of 1039 Bulinus truncatus was infected with Schistosoma sp. but none of 859 Biomphalaria alexandrina was infected. Schistosomiasis mansoni is being focally transmitted in 2 villages in Assiut Governorate and appears to be spreading from Lower to Middle and Upper Egypt. We believe B. alexandrina, which has been present in some of the waterways for at least 15 years, were infected recently by local inhabitants returning from Iraq or by cattle traders or military recruits from the Delta.

Factors affecting the intensity of reinfection with Schistosoma haematobium following treatment with praziquantel.

Infection with Schistosoma haematobium was studied in a rural community of approximately 500 persons in eastern Zimbabwe. The overall prevalence of infection, as determined by urine egg counts, was 40.1%, and of heavy infections (greater than or equal to 50 eggs/10 ml urine) was 11.0%. The prevalence of both heavy and all infections was highest in the 8 to 10-year-old age class. During 1987-88 data were obtained from 102 individuals on intensity of reinfection 14 weeks after treatment with praziquantel, the efficacy of treatment having been determined after 4 weeks. The water contact made by these individuals during 2-week periods immediately following treatment was recorded. The relative abundance of patent infected intermediate host snails, Bulinus globosus, was also monitored. An index of exposure was developed which weighted each water contact by its duration, the type of activity, the time of day, and the abundance of infected snails at the site used. The relationships between rates of reinfection, rates of exposure, and age were examined. Although only 13 individuals showed positive rates of reinfection, there were statistically significant and independent effects of both exposure and age on reinfection rate. Quantitative estimates of reinfection rates suggested that individuals aged 12 years or less acquired substantially more infection (measured as egg output) than individuals more than 12 years old.

Chemotherapy-based control of schistosomiasis haematobia. 3. Snail studies monitoring the effect of chemotherapy on transmission in the Msambweni area, Kenya.

Regular snail sampling was performed at 40 sites, representing the principal snail habitats, during a 4 year chemotherapy programme targetted at school-children in the Msambweni area of the coastal plain of Kenya. Populations of Bulinus africanus group snails, primarily from pools, showed seasonal variations, dropping when sites dried out and rising when they were refilled by the rains. Transmission, judged by the recovery of snails shedding typical fucocercous cercariae, continued throughout the treatment period at very low levels (less than 1% of the snails collected were infected) with peaks in October/November and in January/February after seasonal rains. Spatially, most infected snails were recovered from 2 large pools near the sea, close to the school that responded least well to the initial chemotherapy programme. Later, infected snails were found sporadically in inland pools, rice fields and temporary streams near another school where there was evidence of substantial reinfection as the study progressed. The snail findings are consistent with a reduction but not elimination of transmission associated with the chemotherapy programme.