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.     

Dynamics of egg counts and circulating antigen levels in a recent Schistosoma mansoni focus in northern Senegal

Serum circulating anodic antigen (CAA) levels were compared with faecal egg counts in four subsequent population samples, randomly selected at 8-month intervals, in a recent Schistosoma mansoni focus in northern Senegal. In all four samples, antigen levels showed the same age-intensity profiles as egg counts, with a strong decline in adults. Also across population samples, a consistent relationship was found between egg counts and antigen levels. Assuming the level of CAA to be a direct reflection of worm burden, these findings support the idea that the observed egg count patterns and levels indeed reflect dynamics of worm burdens, and not of egg excretion or worm fecundity. Remarkably similar levels of both egg counts and CAA were observed in the first and last sample, collected in the same season (August--September), but 2 years apart. This suggests that a steady state of S. mansoni infection had already been reached shortly after the onset of the epidemic in this focus (3 years). Significantly lower infection levels were found in the intermediate population samples collected in January and April. The differences in infection levels across the four population samples may be because of seasonal transmission patterns. They would indicate a substantial turnover of worm populations, with an estimated average life span of only 7 months, probably less, in this recently emerged, intense S. mansoni focus.     

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.     

Social research as an intervention tool in tuberculosis control.

Our multidisciplinary project on TB control in the Free State, South Africa, is targeting two dimensions for intervention: firstly, patients, to facilitate compliance and improve quality of care; secondly, the health care system, to identify weaknesses that require remedying and best practices to promote better TB control. This communication illustrates how social scientists can contribute towards the implementation of interventions related to their research, thus influencing TB policy, programme planning and practice more directly.     

Two-year follow-up of Schistosoma mansoni infection and morbidity after treatment with different regimens of oxamniquine and praziquantel

Three study groups in the Rusizi plain (Burundi) were examined parasitologically (duplicate 28 mg Kato slides) and clinically (history, abdominal palpation) 0, 1.5, 3, 6, 12 and 24 months after treatment for Schistosoma mansoni infection. Infected subjects in Maramvya (n = 430) were treated randomly with oxamniquine 20, 30 or 40 mg/kg; those in Bulinga (n = 457) with praziquantel, 20, 30 or 40 mg/kg; those in Bulamata (n = 333) with praziquantel, 30 or 40 mg/kg. In children (less than 20 years) in Maramvya and Bulamata, infection rates and intensities returned almost to pretreatment levels one to 2 years after treatment. In Bulinga, reinfection in children was much less intense. Hardly any reinfection occurred in adults in Bulinga and Maramvya; in Bulamata, half of the cured adults were reinfected, most of them lightly, 2 years after treatment. The initial parasitological advantage of the higher dosages of both drugs disappeared generally 3-12 months after treatment. There was no indication of predisposition to heavy reinfection after treatment of subjects with initial high egg counts. Little relation between pre-treatment egg count and morbidity was observed. The impact of chemotherapy on hepatomegaly was limited and observed only in adults treated with 40 mg/kg of either drug. Spleen rates in children and adults were not affected. Abdominal pain was reduced in almost all treatment groups for 3 to 24 months. The frequency of bloody diarrhoea decreased dramatically in children and adults from all 3 villages. This effect lasted 24 months in Maramvya, 12 months in Bulinga and 6 months in Bulamata, and was not dose-dependent. It is concluded that: (i) repeated population chemotherapy combined with sanitation is necessary to achieve lasting impact on infection rates; (ii) retreatment intervals should be adapted to age group and, possibly, local endemicity levels; (iii) the morbidity impact of population chemotherapy in these conditions was greater on intestinal than on hepatosplenic disease; (iv) lower, cheaper treatment schedules may in the long term be as effective as those with high cure rates.     

The epidemiology of schistosomiasis in Burundi and its consequences for control.

This paper summarizes the results of a series of studies on the epidemiology, morbidity and transmission of Schistosoma mansoni in Burundi, and discusses their consequences for control. The main endemic area is the Imbo lowland, consisting of the Rusizi plain, the urban focus of Bujumbura, and the shores of lake Tanganyika; a small, new focus was discovered in the highlands, around lake Cohoha. Distribution studies on 5-10% population samples with duplicate 28 mg Kato smears in these 4 foci showed prevalences of 33%, 26%, 17%, 19% and mean (positive) egg loads of 110, 105, 92, 144 eggs/g, respectively. The combined population at risk was estimated to be 400,000 people, the total number of detectable cases 90,000. Prevalences and intensities varied greatly at the subregional, local and even sublocal level. The age- and sex-related prevalences and intensities of infection showed typical peaks in children and adolescents, but remained relatively high in adults in many areas; these patterns varied from one area to another and could be related to ecology and water contact. Morbidity studies showed that, in children as well as in adults, schistosomiasis-related morbidity such as (bloody) diarrhoea, hepatomealy and splenomegaly was apparent mainly in areas with prevalences over 30-40%. The intermediate hosts were Biomphalaria pfeifferi (Imbo), B. sudanica (Tanganyika marshes) and B. stanleyi (Cohoha). Population dynamic studies showed strong seasonal variations, the patterns of which were focal and even erratic in space and time. Snail densities and cercarial infection rates (0.85% overall in B. pfeifferi) were low.(ABSTRACT TRUNCATED AT 250 WORDS)     

Are poor responses to praziquantel for the treatment of Schistosoma mansoni infections in Senegal due to resistance? An overview of the evidence

This paper summarizes and concludes in-depth field investigations on suspected resistance of Schistosoma mansoni to praziquantel in northern Senegal. Praziquantel at 40 mg/kg usually cures 70-90% of S. mansoni infections. In an initial trial in an epidemic S. mansoni focus in northern Senegal, only 18% of the cases became parasitologically negative 12 weeks after treatment, although the reduction in mean egg counts was within normal ranges (86%). Among other hypotheses to explain the observed low cure rate in this focus, the possibility of drug resistance or tolerance had to be considered. Subsequent field trials with a shorter follow-up period (6-8 weeks) yielded cure rates of 31-36%. Increasing the dose to 2 x 30 mg/kg did not significantly improve cure rates, whereas treatment with oxamniquine at 20 mg/kg resulted in a normal cure rate of 79%. The efficacy of praziquantel in this focus could be related to age and pre-treatment intensity but not to other host factors, including immune profiles and water contact patterns. Treatment with praziquantel of individuals from the area residing temporarily in an urban region with no transmission, and re-treatment after 3 weeks of non-cured individuals within the area resulted in normal cure rates (78-88%). The application of an epidemiological model taking into account the relation between egg counts and actual worm numbers indicated that the low cure rates in this Senegalese focus could be explained by assuming a 90% worm reduction after treatment with praziquantel; in average endemic situations, such a drug efficacy would result in normal cure rates. Laboratory studies by others on the presence or absence of praziquantel resistance in Senegalese schistosome strains have so far been inconclusive. We conclude that there is no convincing evidence for praziquantel-resistant S. mansoni in Senegal, and that the low cure rates can be attributed to high initial worm loads and intense transmission in this area.     

The morbidity of schistosomiasis mansoni in Maniema (Zaire)

The morbidity of schistosomiasis mansoni was assessed in Makundju (population 547; prevalence 96%, mean egg load 791 epg) and Massimelo (pop. 363; prev. 19%, mean egg load 39 epg), 2 similar villages in the forest zone of Maniema, Zaire. The prevalences of other parasites including malaria (holoendemic) were comparable. "Intermittent diarrhoea" (mostly bloody) was a complaint of 55% and 3% of the populations, respectively, "intermittent abdominal pain" of 63% and 25%, and "fatigue" of 33% and 19%. Enlargement of the left liver lobe was present in 45% and 9% of the populations, right lobe hepatomegaly in 32% and 3%, splenomegaly in 29% and 9%. Hepatomegaly and splenomegaly in Makundju were often very impressive, and most frequent in the 6- to 18-year-old group. Anaemia (haematocrit less than or equal to 35%) was present in 30% and 9% of males and 36% and 21% of females. Mean length and weight were lower in Makundju for boys aged 11 to 18 years. Ergometric results (Astrand cyclometer, male adults only) were comparably low in both villages (mean VO2max. 19.3 and 18.9). Analysis of the data according to egg load within the Makundju community revealed a significant relationship only in the following cases: higher frequencies of diarrhoea, abdominal pain and fatigue in those excreting more than 200 epg compared with those excreting fewer; left lobe splenomegaly gradually increased with egg load in children under 18; in people over 40 it occurred at a higher frequency in those excreting more than 2000 epg than in those excreting fewer.(ABSTRACT TRUNCATED AT 250 WORDS)