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FIGURE 2 in RANDOM SPATIAL DISTRIBUTION OF SCHISTOSOMA MANSONI AND HOOKWORM INFECTIONS AMONG SCHOOL CHILDREN WITHIN A SINGLE VILLAGE
No full textFIGURE 2. Spatial distribution of different infection intensity levels of hookworm among school children living in the village of Fagnampleu, western Côte d'Ivoire.Published as part of Utzinger, Jürg, Müller, Ivo, Vounatsou, Penelope, Singer, Burton H., N'Goran, Eliézer K. & Tanner, Marcel, 2003, RANDOM SPATIAL DISTRIBUTION OF SCHISTOSOMA MANSONI AND HOOKWORM INFECTIONS AMONG SCHOOL CHILDREN WITHIN A SINGLE VILLAGE, pp. 686-692 in Journal of Parasitology 89 (4) on page 690, DOI: 10.1645/ge-75r, http://zenodo.org/record/767889
Serengeti III: Reintegrating People, Disease Management, and Conservation Policy in the Serengeti-Mara Ecosystem
No full textSchistosomiasis control in China : strategy of control and rapid assessment of schistosomiasis risk by remote sensing (RS)and geographic information system (GIS)
Full text linkHuman schistosomiasis remains one of the most prevalent parasitic infections
in the tropics and subtropics. The disease currently is endemic in 76 countries and
territories and continues to be a major public health concern, especially in the
developing world. It is estimated that 650 million people are at risk of infection.
Among the 200 million people actually infected, 120 million are symptomatic and 20
million suffer severe disease. Although morbidity control – in line with
recommendations put forth by the World Health Organization – has been carried out
in China for more than 20 years, it is estimated that 90 million people still live in areas
where they are at risk of infection, and 820,000 people are infected with the parasite,
i.e. Schistosoma japonicum. The estimated area of intermediate host snail habitats
comprise 3,436 km2, concentrated in the 5 lake regions along the Yangtze River that
include the provinces of Anhui, Jiangsu, Jiangxi, Hubei and Hunan. The marshlands
of the Poyang Lake region represent some of the strongholds for the transmission of
S. japonicum. In these settings, for example, the percentages of acute cases and
intermediate host snail habitats represent 79.5% and 96.4%, respectively. With the
World Bank Loan Project (WBLP) to control schistosomiasis in China, the overall
prevalence of S. japonicum was significantly reduced, but in highly endemic areas
the re-infection rates are high.
In the first part of the present thesis, I summarize the 50-year history of China’s
experience and expertise in schistosomiasis control. Particular emphasis is placed on
morbidity control and achievements made by the WBLP carried out between 1992
and 2001. Reviewing this body of literature reveals that morbidity control of
schistosomiasis in China has been successful, and hence this strategy will continue
to form the backbone of protecting people’s health. However, total expenditures have
been considerable, and with the termination of the WBLP there is concern that
schistosomiasis might re-emerge. In the second part of this thesis, I describe the
successful development of a novel compound model to identify the habitats of
Oncomelania hupensis, the intermediate host snail of S. japonicum, and hence the
identification of high-risk areas of disease transmission. There are three findings that
warrant particular notion. First, visual land use classification on multi-temporal
Landsat images was performed for preliminary prediction of O. hupensis habitats.
Second, extraction of the normalized difference vegetation index and the tasseled
cap transformation greenness index were used for improved snail habitat prediction.
Third, buffer zones with distances of 600 and 1,200 m were made around the
predicted snail habitats to differentiate between high (>15%), moderate (3-15%) and
low risk of S. japonicum infection prevalence (< 3%). Preliminary validation of the
compound model against ground-based snail surveys in the Poyang Lake region
revealed that the model had an excellent predictive ability. The model therefore holds
promise for rapid and inexpensive identification of high-risk areas, and can guide
subsequent control interventions, such as whether mass or selective chemotherapy
should be employed. The model can also be used for diseases surveillance in
general and the monitoring of ecological transformations on the transmission
dynamics of S. japonicum, for example in the Three Gorges Dam area
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The effect of irrigated urban agriculture on malaria, schistosomiasis and soil-transmitted helminthiasis in different settings of Côte d'Ivoire
Full text linkMalaria is responsible for more than one million deaths every year, mainly children under the age of five years living in sub-Saharan Africa. At least one billion people harbor one or several of the three main soil-transmitted helminths, namely Ascaris lumbricoides, hookworms and Trichuris trichiura, and about 207 million people are infected with schistosomes. An estimated 70,000 people die each year from amoebiasis, caused by Entamoeba histolytica. Giardiasis, caused by Giardia duodenalis, is responsible for 2.8 million annual infections. Poor rural and urban communities in developing countries bear the highest burden of the above-mentioned diseases. Their causes are multifactorial including lack of access to clean water, improved sanitation and health services, as well as inadequate treatment, protection and prevention. The highest rates of urbanization currently occur in the less developed regions of Africa and Asia, and it is predicted that the majority of the population will be living in small and medium urban centers in the near future. The maintenance of traditional livelihoods, including agriculture, is a typical feature in urban settings across Africa, especially in small towns where population densities and land pressure are lower than in big cities. Urban agriculture contributes to food security and livelihood opportunities for poor urban dwellers. However, the adaptation of disease vectors and intermediate hosts to urban ecosystems has been observed, which might further enhance the negative effects associated with persistent rural lifestyles. For example, the creation of malaria vector breeding sites and contact with contaminated water and soil in areas of irrigated agriculture may increase the transmission of vector-borne, water-related and soil-transmitted parasitic diseases. This PhD focused on the interface of agriculture and human health in two different urban settings of Côte d’Ivoire. The overarching goal was to contribute to a better understanding of the effects of irrigated urban agriculture on the transmission of malaria, schistosomiasis, soil-transmitted helminthiasis and intestinal protozoan infections. The research entailed a considerable amount of fieldwork, carried out between April 2004 and July 2005. In a first step, six zones of irrigated agricultural land use were identified both in Abidjan, the economic capital of Côte d’Ivoire (3.3 million inhabitants), and in the mediumsized town of Man (115,000 inhabitants) in the western part of the country. Next, two standardized mosquito breeding site assessments were conducted in these agricultural zones in the rainy season (September 2004) and in the dry season (February 2005). In each urban setting, a minimum of 120 farming households and additionally 30 non-farming households were randomly selected. Geographic coordinates of houses and the main agricultural plots were recorded. Name, age and sex of all household members were registered. In October
2004, interviews on agricultural land use, farming practices and water storage were
conducted with the heads of the farming households. In a cross-sectional survey done in
May/June 2005, questionnaires were administered to all households to assess the socioeconomic
status, sanitary facilities and common water contact patterns. From each study
participant, a finger prick blood sample and a stool sample were collected. Thick and thin
blood films were stained with Giemsa and examined for Plasmodium spp. under a light
microscopy. The stool samples were prepared based on the Kato-Katz technique and eggs of
Schistosoma mansoni, A. lumbricoides, hookworm and T. trichiura were recorded separately.
Cysts or trophozoites of intestinal protozoa, including Entamoeba histolytica/E. dispar and G.
duodenalis were identified using an ether-formalin concentration method. Risk factors were
identified by fitting multivariate non-random and random effects Bayesian regression models
integrating spatial correlation of infection.
Agricultural land use in Abidjan was characterized by market gardens on lagoon shores
and high-yield vegetable production. The vegetable production areas in Abidjan developed as
a consequence of land access difficulties in unexploited public and private areas near poor
settlements, mainly at lagoon shores. In Man, farming was family- and subsistence-based.
Predominant agricultural activities were traditional irrigated rice farming and vegetable
production in lowlands and along the Kô River.
The typical demographic and socio-economic profile of a vegetable producer in
Abidjan is that he is an immigrant from Burkina Faso, illiterate and lacking a professional
agricultural training. Malaria and intestinal parasitic infections were most prevalent among
the final study cohort of 370 farmers and family members from 121 farming households. We
found overall prevalences of T. trichiura, P. falciparum and hookworm of 42.6%, 24.3% and
17.3%, respectively. The parasites were heterogeneously distributed between the six market
garden zones. Prior health issues were suppressed by the farmers with the daily livelihood
struggle and reported symptoms due to intestinal parasitic infections were of less importance
when compared to malaria. In-depth focus group discussions revealed that the working
environment was discerned as unhealthy, and waste dumps and human defecation grounds
were perceived as main health risks. Farmer communities and their network are indicative for
the degree of social coherence and stability in a vegetable production area because these
zones are characterized by highly dynamic land use patterns.
In the town of Man, Anopheles larvae were present in 50.7% and 42.4% of 369 and 589
examined potential mosquito breeding sites in the rainy and in the dry season, respectively.
The most productive habitats were man-made, i.e. agricultural trenches, irrigation wells, and
flooded and recently transplanted rice plots. The overall prevalence of P. falciparum
infections in the final study cohort of 574 individuals from 112 farming households was
32.1%. Risk factors for P. falciparum in children <15 years of age included living in specific
agricultural zones (i.e. traditional irrigated rice plots, mixed crops and a large rice perimeter),
proximity to permanent man-made ponds and fish ponds, periodic stays overnight in farm
huts and low socio-economic status.
The final study cohort for S. mansoni and soil-transmitted helminthiasis comprised 586
individuals from 113 farming households. The overall prevalences of S. mansoni, hookworm,
E. histolytica/E. dispar and G. duodenalis were 51.4%, 24.7%, 20.2% and 6.3%, respectively.
Members from farming households harbored significantly more often an infection with
E. histolytica/E. dispar and G. duodenalis when compared to non-farming households.
Predictors for an S. mansoni infection included close proximity to the Kô River, contact with
irrigation wells and ponds on the agricultural plots and low educational attainment. Risk
factors for hookworm infection comprised living in agricultural zones of traditional
smallholder irrigated rice plots and a large rice perimeter, using water from domestic wells
and low socio-economic status. Infection prevalences of P. falciparum, S. mansoni and
hookworm were spatially highly heterogeneous between the agricultural zones and highest
infections occurred in a zone of a large rice perimeter. P. falciparum infection intensity and
hookworm infection prevalence were best explained by spatial random effect models. Spatial
correlation between farmers’ houses was not significant.
The findings of the present work illustrated a clear picture of the interconnections
between specific irrigated agricultural land use and agricultural activities, and malaria and
intestinal parasitic infections in different urban settings of Côte d’Ivoire. The outcomes lead
to an enhanced understanding of their epidemiology in local agro-ecological urban settings
and related contextual determinants (i.e. agricultural, behavioural, demographic, socioeconomic
and environmental factors) and allows the design of readily adapted prevention and
control interventions (e.g. tangible vector control strategies and prevention measures for
helminth infections) which actively involve farming communities in the subsequent
implementation and control management
Reachable Outcomes of Combining Multiple Interventions for Control of Malaria and Drug Resistance: Models, Analysis, and a Framework for Adaptive Programs
No full textHow might we take advantage of the currently available anti-malarial interventions to control malaria and parasite drug resistance in endemic areas? Interventions include antimalarial drugs, insecticide-treated bednets, housing features, indoor residual spraying of insecticides, and reduction of larval habitats. Are there possible advantages to combining interventions with respect to reducing malaria burden and drug resistance rate? How might we intentionally design an adaptive intervention program which efficiently improves over time? We develop new models and frameworks to propose some possible answers. We propose a framework for multi-intervention adaptive programs for malaria and drug resistance control. This framework incorporates sound components from statistical and engineering methods, mechanistic epidemiological models like we develop, and intervention-focused operational research. All our models are structured to take as input baseline transmission setting and coverage of interventions and return as output malaria burden and drug resistance over time. Model forms include simple extensions of early compartmental models suitable for low endemic settings, analytical approximations, a novel framework of modular compartmental models for low and high endemic settings, and a microsimulation which tracks an interacting group of individual humans and mosquitoes exchanging mutating parasites for various transmission settings. Details simulated include malaria transmission, superinfection, immunity dynamics, drug resistance emergence and/or spread, drug pharmacodynamics/pharmacokinetics, and multiple interventions. We use published data and measurements for model parameterization and validation. Our model analysis systematically explores the large space of possible multi-intervention programs and their possible effects on malaria burden and drug resistance. Our models predict that interventions can combine constructively to reduce malaria burden. Interestingly, except for the simple analytical approximations, our models also predict that drug resistance depends not only on the fraction of clinical infections drug-treated but also on vector-related interventions in a possibly complex manner depending on transmission settings, overall coverage of interventions, and whether the focus is spread of resistance or also emergence of resistance. Our modular compartmental models predict theoretically – along with some possible caveats to avoid – how vector-related interventions, in a program with drug treatment, might be used to generate possible advantages with respect to both reducing malaria burden and drug resistance spread
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