Inclusion of edaphic predictors for enhancement of models to determine distribution of soil-transmitted helminths: the case of Zimbabwe.

BACKGROUND: Reliable mapping of soil-transmitted helminth (STH) parasites requires rigorous statistical and machine learning algorithms capable of integrating the combined influence of several determinants to predict distributions. This study tested whether combining edaphic predictors with relevant environmental predictors improves model performance when predicting the distribution of STH, Ascaris lumbricoides and hookworms at a national scale in Zimbabwe. METHODS: Geo-referenced parasitological data obtained from a 2010/2011 national survey indicating a confirmed presence or absence of STH among school children aged 10-15 years was used to calibrate ten species distribution models (SDMs). The performance of SDMs calibrated with a set of environmental and edaphic variables was compared to that of SDMs calibrated with environmental variables only. Model performance was evaluated using the true skill statistic and receiver operating characteristic curve. RESULTS: Results show a significant improvement in model performance for both A. lumbricoides and hookworms for all ten SDMs after edaphic variables were combined with environmental variables in the modelling of the geographical distribution of the two STHs at national scale. Using the top three performing models, a consensus prediction was developed to generate the first continuous maps of the potential distribution of the two STHs in Zimbabwe. CONCLUSIONS: The findings from this study demonstrate significant model improvement if relevant edaphic variables are included in model calibration resulting in more accurate mapping of STH. The results also provide spatially-explicit information to aid targeted control of STHs in Zimbabwe and other countries with STH burden.

Efficacy of integrated school based de-worming and prompt malaria treatment on helminths -Plasmodium falciparum co-infections: A 33 months follow up study.

BACKGROUND: The geographical congruency in distribution of helminths and Plasmodium falciparum makes polyparasitism a common phenomenon in Sub Saharan Africa. The devastating effects of helminths-Plasmodium co-infections on primary school health have raised global interest for integrated control. However little is known on the feasibility, timing and efficacy of integrated helminths-Plasmodium control strategies. A study was conducted in Zimbabwe to evaluate the efficacy of repeated combined school based antihelminthic and prompt malaria treatment. METHODS: A cohort of primary schoolchildren (5-17 years) received combined Praziquantel, albendazole treatment at baseline, and again during 6, 12 and 33 months follow up surveys and sustained prompt malaria treatment. Sustained prompt malaria treatment was carried out throughout the study period. Children's infection status with helminths, Plasmodium and helminths-Plasmodium co-infections was determined by parasitological examinations at baseline and at each treatment point. The prevalence of S. haematobium, S. mansoni, STH, malaria, helminths-Plasmodium co-infections and helminths infection intensities before and after treatment were analysed. RESULTS: Longitudinal data showed that two rounds of combined Praziquantel and albendazole treatment for schistosomiasis and STHs at 6 monthly intervals and sustained prompt malaria treatment significantly reduced the overall prevalence of S. haematobium, S. mansoni, hookworms and P. falciparum infection in primary schoolchildren by 73.5%, 70.8%, 67.3% and 58.8% respectively (p < 0.001, p < 0.001, p < 0.001, p < 0.001 respectively). More importantly, the prevalence of STH + schistosomes, P. f + schistosomes, and P. f + STHs + schistosomes co-infections were reduced by 68.0%, 84.2%, and 90.7%, respectively. The absence of anti-helminthic treatment between the 12 mth and 33 mth follow-up surveys resulted in the sharp increase in STHs + schistosomes co-infection from 3.3% at 12 months follow up survey to 10.7%, slightly more than the baseline level (10.3%) while other co-infection combinations remained significantly low. The overall prevalence of heavy S. haematobium, S. mansoni and hookworms infection intensities were significantly reduced from: 17.9-22.4% to 2.6-5.1%, 1.6-3.3% to 0.0% and 0.0-0.7% to 0.0% respectively. CONCLUSION: Biannual Integrated school based antihelminthic and sustained prompt malaria treatment has a potential to reduce the burden of helminths-plasmodium co-infections in primary school children. In areas of stable malaria transmission, active case finding is recommended to track and treat asymptomatic malaria cases as these may sustain transmission in the community.

Knowledge attitudes and practices of grade three primary schoolchildren in relation to schistosomiasis, soil transmitted helminthiasis and malaria in Zimbabwe.

BACKGROUND: Helminth infection rates in grade three children are used as proxy indicators of community infection status and to guide treatment strategies in endemic areas. However knowledge, attitudes and practices (KAP) of this target age group (8-10 years) in relation to schistosomiasis, soil transmitted helminthiasis (STHs) and malaria is not known at a time when integrated plasmodium - helminth control strategies are being advocated. This study sought to assess KAP of grade 3 children in relation to schistosomiasis, STHs and malaria in order to establish an effective school based health education for disease transmission control. METHODS: Grade 3 children (n = 172) attending four randomly selected primary schools (one in rural and 3 in the commercial farming areas) in Zimbabwe were interviewed using a pre-tested interviewer administered questionnaire. The urine filtration technique was used to determine S. haematobium infection status. Infection with S. mansoni and STHs was determined using a combination of results from the Kato Katz and formol ether concentration techniques. P. falciparum was diagnosed by examination of Giemsa stained thick blood smears. RESULTS: It was observed that 32.0%, 19.2% and 4.1% of the respondents had correct knowledge about the causes of schistosomiasis, malaria and STHs, respectively, whilst 22.1%, 19.2% and 5.8% knew correct measures to control schistosomiasis, malaria and STHs. Sixty-two percent and 44.8% did not use soap to wash hands after toilet and before eating food respectively, whilst 33.1% never wore shoes. There were no functional water points and soap for hand washing after toilet at all schools. There was a high prevalence distribution of all parasites investigated in this study at Msapa primary school - S. haematobium (77.8%), S. mansoni (33.3%) hookworms (29.6%) and P. falciparum (48.1%). Reports that participant had suffered from schistosomiasis and malaria before were significant predictors of these diseases (p = 0.001 and p = 0.042, respectively). Report that participant had blood in urine on the day of examination was a significant predictor of schistosomiasis (p = 0.045). CONCLUSION: There is a critical need for targeting health messages through schools in order to reach the most susceptible schoolchildren. This will empower the schoolchildren with the basic knowledge and skills ultimately protecting them from acquiring schistosomiasis, STHs and malaria.