Schistosomiasis.

Schistosomiasis is a tropical parasitic disease, caused by blood-dwelling worms of the genus Schistosoma. The main human species are S mansoni (occurring in Africa and South America) and S japonicum (South and East Asia) causing intestinal and hepatosplenic schistosomiasis, and S haematobium (Africa) causing urinary schistosomiasis. Severe symptoms develop in predilected people with heavy and long-standing infections. Acute schistosomiasis, a flulike syndrome, is a regular finding in travel clinics. Although prevalences can be high, most infected people show limited, intermittent, or aspecific symptoms. The diagnosis of schistosomiasis relies on microscopic examination of stools or urine, serologic tests, and imaging. Praziquantel is the drug of choice, active against all species in a single or a few oral doses. Current control strategies consist mainly of preventive therapy in communities or groups at risk.

The contribution of water contact behavior to the high Schistosoma mansoni Infection rates observed in the Senegal River Basin.

BACKGROUND: Schistosomiasis is one of the major parasitic diseases in the world in terms of people infected and those at risk. Infection occurs through contact with water contaminated with larval forms of the parasite, which are released by freshwater snails and then penetrate the skin of people. Schistosomiasis infection and human water contact are thus essentially linked, and more knowledge about their relationship will help us to develop appropriate control measures. So far, only few studies have related water contact patterns to infection levels. METHODS: We have conducted detailed direct water contact observations in a village in Northern Senegal during the first years of a massive Schistosoma mansoni outbreak to determine the role of human water contact in the extent of the epidemic.We quantified water contact activities in terms of frequency and duration, and described how these vary with age and sex. Moreover, we assessed the relationship between water contact- and infection intensity patterns to further elucidate the contribution of exposure to the transmission of schistosomiasis. RESULTS: This resulted in over 120,000 recorded water contacts for 1651 subjects over 175 observation days. Bathing was the main activity, followed by household activities. Frequency and duration of water contact depended on age and sex rather than season. Water contacts peaked in adolescents, women spent almost twice as much time in the water as men, and water contacts were more intense in the afternoon than in the morning, with sex-specific intensity peaks. The average number of water contacts per person per day in this population was 0.42; the average time spent in the water per person per day was 4.3 minutes. CONCLUSIONS: The observed patterns of water contact behavior are not unusual and have been described before in various other settings in sub-Saharan Africa. Moreover, water contact levels were not exceptionally high and thus cannot explain the extremely high S. mansoni infection intensities as observed in Northern Senegal. Comparison with fecal egg counts in the respective age and sex groups further revealed that water contact levels did not unambiguously correspond with infection levels, indicating that factors other than exposure also play a role in determining intensity of infection.

The role of hygienic bathing after defecation in the transmission of Schistosoma mansoni.

Transmission of Schistosoma mansoni depends on fecal eggs reaching water, but the way this happens is poorly understood. We studied the role of hygienic bathing after defecation in the contamination of water with S. mansoni eggs. Individuals in an endemic community in Northern Senegal (n=991) were examined for S. mansoni infection and a random sample (22%) was interviewed about stool disposal practices and hygienic behavior. We assessed the presence and viability of S. mansoni eggs adhering to the peri-anal region of 13 infected volunteers, by counting the miracidia in the water they had used for hygienic washing; for 10 of them (77%) miracidia were demonstrated. From the population infection distribution, average number of defecations per day, proportion of individuals bathing after defecation, and association between miracidial counts and infection intensity, we calculated a daily population miracidial output of approximately 30,000 through hygienic bathing. For comparison, one complete stool reaching the water was calculated to yield approximately 2500 miracidia. Thus, 12 individuals in this population should defecate into the water every day to produce the same number of miracidia as through hygienic bathing. Our results suggest a major role of hygienic bathing after defecation in the transmission of S. mansoni.

Association of atopy, asthma, allergic rhinoconjunctivitis, atopic dermatitis and intestinal helminth infections in Cuban children.

OBJECTIVE: To examine the relationship of past and current intestinal helminth infections with asthma, allergic rhinoconjunctivitis, atopic dermatitis and atopy. METHODS: Cross-sectional study of 1320 children aged 4-14 years from two Cuban municipalities. Helminth infections were determined by stool examination and parental questionnaire. Asthma, rhinoconjunctivitis and atopic dermatitis were diagnosed by International Study of Asthma and Allergies in Childhood questionnaire, asthma additionally by spirometry, atopy by skin prick testing. RESULTS: Questionnaire-based frequencies were 21% for asthma, 14% for allergic rhinoconjunctivitis and 8% for atopic dermatitis. According to spirometry, 4% had asthma; 20% had a positive skin prick test. A history of infection for Enterobius vermicularis was associated with increased risk of atopic dermatitis (OR 1.88, P = 0.001) and allergic rhinoconjunctivitis (OR 1.34, P = 0.046), and hookworm with increased risk of allergic rhinoconjunctivitis (OR 2.77, P = 0.021). A positive stool examination for Ascaris lumbricoides infection was negatively associated with atopic dermatitis (OR 0.22, P = 0.007). Asthma and atopy were unrelated to helminth infections. CONCLUSION: Current A. lumbricoides infection protects against atopic dermatitis in Cuban children, while past infection with E. vermicularis and hookworm are risk factors for allergic rhinoconjunctivitis and/or atopic dermatitis. Apparently, interactions differ depending on the type of helminth and atopic disease and on the time of helminth infestation.

Associations between specific antibody responses and resistance to reinfection in a Senegalese population recently exposed to Schistosoma mansoni.

We examined associations between schistosome-specific antibody responses and reinfection in Senegalese individuals recently exposed to Schistosoma mansoni. The effects of treatment, age, intensity of infection and duration of exposure on schistosome-specific antibody responses were also investigated by comparing immune responses in individuals exposed for less than 3 years with responses in people exposed for more than 8 years. All individuals were bled before treatment as well as 6 and 12 weeks after. We used a statistical model that included interaction terms between time, age, infection intensity and duration of exposure. The overall patterns of most specific antibody responses by age were similar to those previously published for S. mansoni, Schistosoma japonicum and Schistosoma haematobium infections in different endemic areas. In general, a boost in specific antibody responses against adult worm antigen (SWA) was observed at 6 weeks after treatment whereas the majority of isotype responses against egg antigen (SEA) were not affected by treatment. Our analysis showed that the effect of treatment on schistosome-specific antibody responses is influenced by age, infection intensity and duration of exposure. We found no evidence that treatment matures the specific antibody response of children recently infected with S. mansoni. Our results indicate that the build-up of potentially protective immunoglobulin E (IgE) responses was associated with duration of exposure, or, in other words, experience of infection. Interestingly, in recently exposed individuals there was a significant association between IgA responses to SWA and resistance to reinfection. Resistance to reinfection and production of IgA-SWA was associated with adulthood independently of exposure patterns, suggesting that susceptibility to S. mansoni and the development of protective immune responses is age-dependent.

Prevalence and risk factors of intestinal parasites in Cuban children.

OBJECTIVES: To determine the prevalence of intestinal parasite infections and their risk factors in children in urban and rural settings in two Cuban municipalities. METHODS: A total of 1320 Cuban schoolchildren aged 4-14 were tested by stool examination for intestinal parasite infections and evaluated by parental questionnaire for a number of common environmental, sanitary, socioeconomic and behavioural risk factors. Multivariate regression was applied to examine the relationship between the respective parasite infections and the risk factors. RESULTS: Prevalences of intestinal parasite infections were 58% in Fomento and 45% in San Juan y Martínez; for helminth infections, these were 18% and 24% and for protozoa infections, 50% and 29%, respectively. Helminth infections were associated with high parental education (maternal: OR 0.68, CI 0.50-0.93; paternal: OR 0.71, CI 0.52-0.96), absence of toilet (OR 1.57, CI 1.12-2.19), consumption of water from a well or river (OR 0.56, CI 0.41-0.77) and eating unpeeled/unwashed fruit (OR 1.37, CI 1.01-1.87); protozoa infections were only associated with high maternal education (OR 0.72, CI 0.57-0.91). CONCLUSIONS: Paediatric intestinal parasite infections are still prevalent in certain areas in Cuba and associated with a number of common environmental, socioeconomic and sanitary risk factors.

Human schistosomiasis.

Schistosomiasis or bilharzia is a tropical disease caused by worms of the genus Schistosoma. The transmission cycle requires contamination of surface water by excreta, specific freshwater snails as intermediate hosts, and human water contact. The main disease-causing species are S haematobium, S mansoni, and S japonicum. According to WHO, 200 million people are infected worldwide, leading to the loss of 1.53 million disability-adjusted life years, although these figures need revision. Schistosomiasis is characterised by focal epidemiology and overdispersed population distribution, with higher infection rates in children than in adults. Complex immune mechanisms lead to the slow acquisition of immune resistance, though innate factors also play a part. Acute schistosomiasis, a feverish syndrome, is mostly seen in travellers after primary infection. Chronic schistosomal disease affects mainly individuals with long-standing infections in poor rural areas. Immunopathological reactions against schistosome eggs trapped in the tissues lead to inflammatory and obstructive disease in the urinary system (S haematobium) or intestinal disease, hepatosplenic inflammation, and liver fibrosis (S mansoni, S japonicum). The diagnostic standard is microscopic demonstration of eggs in the excreta. Praziquantel is the drug treatment of choice. Vaccines are not yet available. Great advances have been made in the control of the disease through population-based chemotherapy but these required political commitment and strong health systems.

Low awareness of intestinal schistosomiasis in northern Senegal after 7 years of health education as part of intense control and research activities.

We evaluated the awareness of and knowledge about intestinal schistosomiasis in a highly infected rural community of northern Senegal where a variety of health information and education activities had taken place for 7 years as a component of different research and control programmes. As the infection had been introduced only recently, an initial 'zero' knowledge can be assumed. Most of the health education activities had been performed with adapted messages through local health and community workers. By a questionnaire, 566 individuals were asked simple questions on symptoms, mode of transmission, the sources of information and health-seeking behaviour. About 86% of the respondents stated that they knew what schistosomiasis was, and 92% that in case of illness they would seek treatment at the health centre. However, only half of the people accurately quoted symptoms associated with intestinal schistosomiasis: diarrhoea, abdominal pain and bloody stools. The majority of respondents realized that the disease was somehow linked with water and (lack of) hygiene, but only 44% of respondents reported water contact as the source of infection. Ultimately, only 30% of the respondents gave adequate answers about both symptoms and mode of transmission. We conclude that even intense and long-lasting education efforts for a specific and straightforward problem as schistosomiasis are not enough to have profound impact on the knowledge of rural traditional communities.

Evaluation of staff performance and material resources for integrated schistosomiasis control in northern Senegal.

BACKGROUND: A project to improve integrated control of schistosomiasis in the primary health care system of northern Senegal was implemented from February 1995 until September 1999, shortly after a Schistosoma mansoni outbreak. The activities included additional training of doctors and nurses in symptom-based treatment and making praziquantel (PZQ) available for an affordable price. OBJECTIVE: To investigate staff performance and the availability and costs of diagnostic materials and PZQ at the end of this intervention project. METHODS: We performed structured interviews with staff from 55 health care facilities in five districts. RESULTS: Respondents from 23 health care facilities reported both S. haematobium and S. mansoni in the coverage area, 32 reported only S. haematobium and three only S. mansoni. The average cost to patients for consultation, diagnosis, treatment and transportation to a referral health care facility was approximately 1.60 Euro. Fifty-seven per cent of the health care facilities with reported S. haematobium in the coverage area treated patients presenting with haematuria on symptoms; 56% of the health care facilities with reported S. mansoni in the coverage area treated patients presenting with blood in stool on symptoms. Thirteen per cent performed a diagnostic test for patients presenting with haematuria and 12% for patients presenting with blood in stool. The remainder, approximately one-third of the health care facilities, referred their patients to another facility for a diagnostic test. Implementation of symptom-based treatment in all health care facilities will reduce the total costs by 0.43 Euro (29%) for patients infected with S. haematobium and 0.78 Euro (46%) for patients infected with S. mansoni. Of the 53 health care facilities with schistosomiasis in their area, 37 had PZQ in stock of which 33 (88%) sold PZQ for the recommended retail price of 0.15 Euro per tablet (or 0.60 Euro per course of four tablets) or lower. CONCLUSION: Four years after the start of the intervention project, patients presenting with schistosomiasis related symptoms can generally expect proper diagnosis and treatment at all levels of the health care system in Northern Senegal, either at the initial visited health care facility or after referral. However, a further reduction of the total costs of treatment is still possible by a better implementation of symptom-based treatment and further reduction of the costs of PZQ.

High prevalence and morbidity of Schistosoma mansoni along the Albert Nile in Uganda.

An epidemiological cross sectional study of Schistosoma mansoni was conducted in two hyper endemic fishing villages of Rhino Camp and Obongi both in West Nile district in northern Uganda in 1991 and 1992. People with various water contacts were registered. A small group of civil servants and clergies with less water contact in the river Nile were studied for control of infection and morbidity. An overall prevalence of 81.5% of the 1367 people studied in both fishing villages of Rhino Camp and Obongi were excreting from 100 to > or = 500 Schistosoma mansoni eggs per gram (epg). 253 18.5% did not have Schistosoma mansoni eggs in their faeces. The influence of socioeconomic factors on infections in the study population was high among poorer illiterates who have frequent water contacts activities with River Nile. The sonomorphological abnormalities of periportal thickening (PT) due to Schistosoma mansoni were performed using ultrasound. 664 patients were found to have various stages of (PT stages 0, I, II and III). A total of 703 (51.4%) patients did not have any periportal thickening (PT 0) in their livers despite the fact that 450 (32.9%) of them had Schistosoma. mansoni eggs in their faeces. The gravities of schistosomiasis in the two villages were similar showing greater morbidity in the younger adults.

Age-related worm load and worm fecundity patterns in human populations, as indicated by schistosome circulating antigens

Recently, our group determined the relationship between serum CAA levels and fecal egg counts in two foci very intense Schistosoma mansoni transmission: Maniema (Zaire), an area endemic for S. mansoni since several decades, and Ndombo (Senegal), where transmission has only been established since a few years. The objetive was to study and compare age-related worm load and worm fecundity patterns in these two different endemic settings. Here, we will summarize the most important findings and conclusions of this study.