[Schistosomiasis mansoni in urban territory. 2. A theoretical approach to the accumulation, concentration, and centralization of capital and the production of disease]

Urban schistosomiasis: An ecological study describing a new challenge to the control of this neglected tropical disease

Background

Social and environmental vulnerabilities contribute to the persistence and increase of Schistosomiasis, which has been a public health problem in Brazil and worldwide. In this study, we aimed to monitor the entry, installation, and maintenance of schistosomiasis transmission in an urban area on the Brazilian coast over two decades (2000-2010/2010-2020).

Methods

This population-based cross-sectional study was conducted in Porto de Galinhas, state of Pernambuco, Brazil, to investigate the dynamics of schistosomiasis transmission in the urban area. Through 3 malacological and parasitological surveys and using geoprocessing technologies, schistosomiasis transmission foci (STF), as well as cases of the disease were identified and quantified. Statistical and geoprocessing tools were used to analyse the data.

Findings

Overall, the number of STF decreased from 15 (2000) to 11 (2010) and then to 9 (2020). Although the infection ratio of snails in 2000 has decreased from 16·1% to 5·8% in 2010, we observed an increase to 7·2% in 2020. Additionally, 6,499 individuals were analysed (2012 in 2000; 2459 in 2010, and 2028 in 2020) and the prevalence of human infection has decreased over years, from 32·5% (2000), 16·6% (2010) to 8·8% (2020). The disorderly urbanization process was directly related to the spatial distribution of STF and schistosomiasis cases, causing a new scenario where people became infected by walking on unpaved and flooded streets.

Interpretation

Although we observed a decreasing in schistosomiasis cases and STF, this NTD became a health problem related to urbanization in the study area. The challenge to overcome this new sort of transmission will require a greater understanding of the disorderly migration, spatial occupation, and degradation of the environment.

Funding

National Council for Scientific and Technological Development (CNPq), Ministry of Science, Technology, Innovations and Communications, Brazil.

Geographic Information System-based association between the sewage network, geographical location of intermediate hosts, and autochthonous cases for the estimation of risk areas of schistosomiasis infection in Ourinhos, São Paulo, Brazil

INTRODUCTION:

Ourinhos is a municipality located between the Pardo and Paranapanema rivers, and it has been characterized by the endemic transmission of schistosomiasis since 1952. We used geospatial analysis to identify areas prone to human schistosomiasis infections in Ourinhos. We studied the association between the sewage network, co-occurrence of Biomphalaria snails (identified as intermediate hosts [IHs] of Schistosoma mansoni), and autochthonous cases.

METHODS:

Gi spatial statistics, Ripley’s K12-function, and kernel density estimation were used to evaluate the association between schistosomiasis data reported during 2007-2016 and the occurrence of IHs during 2015-2017. These data were superimposed on the municipality sewage network data.

RESULTS:

We used 20 points with reported IH; they were colonized predominantly by Biomphalaria glabrata, followed by B. tenagophila and B. straminea. Based on Gi statistics, a significant cluster of autochthonous cases was superimposed on the Christoni and Água da Veada water bodies, with distances of approximately 300 m and 2200 m from the points where B. glabrata and B. straminea were present, respectively.

CONCLUSIONS:

The residence geographical location of autochthonous cases allied with the spatial analysis of IHs and the coverage of the sewage network provide important information for the detection of human-infection areas. Our results demonstrated that the tools used for direct surveillance, control, and elimination of schistosomiasis are appropriate.

The relative contribution of immigration or local increase for persistence of urban schistosomiasis in Salvador, Bahia, Brazil

Urbanization is increasing across the globe, and diseases once considered rural can now be found in urban areas due to the migration of populations from rural endemic areas, local transmission within the city, or a combination of factors. We investigated the epidemiologic characteristics of urban immigrants and natives living in a neighborhood of Salvador, Brazil where there is a focus of transmission of Schistosoma mansoni. In a cross-sectional study, all inhabitants from 3 sections of the community were interviewed and examined. In order to determine the degree of parasite differentiation between immigrants and the native born, S. mansoni eggs from stools were genotyped for 15 microsatellite markers. The area received migrants from all over the state, but most infected children had never been outside of the city, and infected snails were present at water contact sites. Other epidemiologic features suggested immigration contributed little to the presence of infection. The intensity and prevalence of infection were the same for immigrants and natives when adjusted for age, and length of immigrant residence in the community was positively associated with prevalence of infection. The population structure of the parasites also supported that the contribution from immigration was small, since the host-to-host differentiation was no greater in the urban parasite population than a rural population with little distant immigration, and there had been little differentiation in the urban population over the past 7 years. Public health efforts should focus on eliminating local transmission, and once eliminated, reintroduction from distant migration is unlikely.

Urban transmission of schistosomiasis is becoming more recognized as rural disease is becoming less common and urbanization increases. Characteristics of infection of the immigrant population to cities and genetic characteristics of the parasite population itself indicate local transmission is the most important factor for the presence of the parasite rather than arrival of infected immigrants. While there is 70% coverage of adequate sanitation, this was insufficient to interrupt transmission. If eliminated, this focus is unlikely to readily reappear due to immigration.

Genetic population structure of cercariae from an urban foci of Schistosoma mansoni, Brazil

Rapid urbanization in Brazil has meant that many persons from rural areas where Schistosoma mansoni is endemic have migrated to cities. Discovery of a focus of active transmission in the city of Salvador prompted a citywide survey for active and potential transmission sites. Cercariae shed from infected snails collected from four locations were used to determine how these samples were related and if they were representative of the parasite population infecting humans. Each cercarial collection was greatly differentiated from the others, and diversity was significantly lower when compared with eggs from natural human infections in one site. Egg samples collected 7 years apart in one neighborhood showed little differentiation (Jost's D = 0.01-0.03). Given the clonal nature of parasite reproduction in the snail host and the short-term acquisition of parasites, cercariae from collections at one time point are unlikely to be representative of the diversity in the human population.

[Schistosoma mansoni in the context of the Brazilian health policy]

There are many factors involved in the determination of the emergence and reemergence of infectious diseases. In the case of Schistosomiasis biological factors are highlighted as related to the habitat, to the microorganisms and hosts adaptations and mutations, to the immunologic reply of the host and to the bio-ecology adaptations of intermediate hosts. These are added to the not less important factors related to the management politics, occupation of the environment and allocation of financial resources. Brazil congregates, today, an important echo-epidemiologic conditions for the reemergence of Schistosomiasis. The expansion of its borders reaches the urban and agricultural environments, destined to work or leisure, also damaging income sectors as the ecotourism. The advances in the researches concerning the intermediate and definitive hosts of the Schistosoma mansoni, to change them into public benefits, need the public sustainability, compromised, interdisciplinary, and strengthened in the government's different spheres. The organized civil society has fundamental paper in the control of the government actions.

[Urban transmission of schistosomiasis in children from a neighborhood of Salvador, Bahia]

In the Subúrbio Ferroviário region of Salvador (Bahia, Brasil) occurrences of schistosomiasis were found. This fact motivated the investigation of the prevalence of the eggs in a group of 268 resident students in one of its neighborhoods (São Bartolomeu). The parasitological test analyzed by the Kato-Katz methodology, showed positive results in 30.2% of the children, ranging from 24 to 2,160 eggsSchistosoma mansoni/gram of feces. Infection was predominant in boys and in those 10 years old and over. Observation revealed that infection predominated in children that live close to natural water bodies. This region was where the three registered cases of hepatosplenicos occurred. Moreover, all the 81 children infected with Schistosoma mansoni eggs were born and live in the study area. Since this neighborhood presents all the elements of the epidemiological chain of Schistosoma mansoni, the evidences strongly suggests the urban transmission of this infection.

Discursive media strategies in the journalistic construction of schistosomiasis in Jaboticatubas, Minas Gerais

Using media discourse analysis for material published by the press on schistosomiasis in the city of Jaboticatubas, the possible determining factors of narrative and discursive constructions in the diffusion of information are discussed. It was observed that media discourse treats schistosomiasis in 1962 as something from the natural order. By 1997 and 1998, the media discourse strategies reveal ideological treatment in favor of certain social segments. Situations are identified in which social agents in specific contexts construct the meanings of this endemic disease. It was concluded that the economic organization of space was a determining factor in the production and circulation of the media discourses.

Acute schistosomiasis outbreak in the metropolitan area of Belo Horizonte, Minas Gerais: alert about the risk of unnoticed transmission increased by growing rural tourism

The present article describes the occurrence of 17 cases of acute schistosomiasis in the metropolitan area of Belo Horizonte, state of Minas Gerais, Brazil. All individuals affected took a bath in a swimming pool of a holiday resort that was provided with water from a nearby brook. The apparently clean water and the absence of snails in the pool gave the wrong impression that there was no risk for infection. During a malacological survey at the site snails of the species Biomphalaria glabrata were found and tested positive for Schistosoma mansoni. All the patients live in the middle-class area of Barreiro, metropolitan area of Belo Horizonte and have medium grade school education. The difficulties in establishing the right diagnosis is expressed by the search for medical attention in 17 different medical facilities, the wide range of laboratory test and the inadequate treatment administration. A lack of knowledge about the disease was found in all groups studied. The booming rural tourism in endemic areas is identified as a probable risk factor for infection, especially for individuals of the non-immune middle and upper class parts of the society in urban centers. Special attention is given to a multidisciplinary approach to the complex issue of disease control and prevention.

Schistosomiasis mansoni in Bananal (State of São Paulo, Brazil): I. Efficiency of diagnostic and treatment procedures

Bananal is an important focus of Schistosoma mansoni in the State of São Paulo. Accordingly, programmed active search for human cases, annual coproscopic surveys and treatment of infected cases were started in 1998, aiming at producing a sharp prevalence rate drop by the year 2000. S. mansoni eggs were searched for in two Kato-Katz slides per patient. Cases were followed up according to the routine of the local Family Health Program. In 1998, 130 samples out of 3,860 showed S. mansoni eggs; in 1999, 105 out of 3,550, and in 2000, 64 out of 3,528. Prevalence rates were 3.4%, 2.9%, and 1.8%, and average egg-counts 59, 64, and 79 eggs per gram of feces respectively. Prevalence rates decreased steadily after treatment, but persistently positive cases showed no significant decrease in parasite burdens. Egg count variation depended on sex and age bracket. Persistent residual cases admittedly preclude the eradication of this infection by only searching for and treating carriers. In addition, resistance to therapy and low sensitivity of fecal examinations, can not be ignored. Moderate to heavy worm burdens, frequently associated with hepatomegaly elsewhere, produced no serious cases in Bananal.

Participação popular no controle da esquistossomose através do Sistema Único de Saúde (SUS), em Taquaraçu de Minas, (Minas Gerais, Brasil), entre 1985-1995: construção de um modelo alternativo

Foi avaliado o programa de controle da esquistossomose realizado em Taquaraçu de Minas, MG, entre 1985 e 1995. A medida de controle adotada foi a participação popular nas ações de controle: tratamento seletivo, saneamento e educação popular. A equipe de saúde local foi capacitada para gerenciar o programa, conforme proposta do SUS. O fornecimento de água potável foi oferecido a 97% das residências no núcleo do Município. Em 1995, foi realizada análise para identificação dos fatores de risco responsáveis pela manutenção da transmissão da esquistossomose. A prevalência da infecção entre 1985-1995 apresentou-se sete vezes menor, passando de 30,9% para 4,3%, respectivamente. A intensidade de infecção também sofreu significativa redução, passando de 91,2 ± 6,1 para 30,7 ± 2,5 (p = 0,00) no mesmo período. A municipalização desse programa de controle da esquistossomose através do SUS, usando-se um tratamento seletivo, fornecimento de água potável intradomiciliar com participação popular nas medidas de controle, seguido de atendimento da demanda espontânea, apresentou resultados duradouros, apontando a possibilidade de uso deste modelo para outras áreas endêmicas com características semelhantes.