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Epidemiology and Control of Human Schistosomiasis In Mazigo et al. Parasites & Vectors 2012, 5:274 http://www.parasitesandvectors.com/content/5/1/274 REVIEW Open Access Epidemiology and control of human schistosomiasis in Tanzania Humphrey D Mazigo1,2,3,4*, Fred Nuwaha2, Safari M Kinung’hi3, Domenica Morona1, Angela Pinot de Moira4, Shona Wilson4, Jorg Heukelbach5 and David W Dunne4 Abstract In Tanzania, the first cases of schistosomiasis were reported in the early 19th century. Since then, various studies have reported prevalences of up to 100% in some areas. However, for many years, there have been no sustainable control programmes and systematic data from observational and control studies are very limited in the public domain. To cover that gap, the present article reviews the epidemiology, malacology, morbidity, and the milestones the country has made in efforts to control schistosomiasis and discusses future control approaches. The available evidence indicates that, both urinary and intestinal schistosomiasis are still highly endemic in Tanzania and cause significant morbidity.Mass drug administration using praziquantel, currently used as a key intervention measure, has not been successful in decreasing prevalence of infection. There is therefore an urgent need to revise the current approach for the successful control of the disease. Clearly, these need to be integrated control measures. Keywords: Schistosomiasis, S. mansoni, S. Mansoni, epidemiology, morbidity, control, Tanzania Review accessed by public health intervention managers and Background policy makers. Availability of this information will not Human schistosomiasis is second only to malaria in sub- only help in implementation of control programs but Saharan Africa (SSA) for causing severe morbidities. also will serve to guide control activities in areas with Of the world's 207 million estimated cases of schisto- the greatest needs and allocation of resources such as somiasis, 93% occur in SSA and the United Republic of drugs. In attempts to cover that gap, the present article, Tanzania is the second country that has the highest bur- reviews the epidemiology, transmission dynamics, past den of schistosomiasis in the region, Nigeria being the and current control approaches and the progress Tanzania first [1,2]. Two major schistosome species are prevalent has made to control the disease. Clinical features and in the region, Schistosoma mansoni and Schistosoma treatments are discussed. Our review supports the need to haematobium causing intestinal and urogenital schisto- reverse the current control approach based on preventive somiasis, respectively [1,2]. In Tanzania, numerous sur- chemotherapy, to an integrated multidisciplinary control veys have been conducted in the past and more recently approach. to describe the epidemiology, transmission (malacology), clinical trials of anti-schistosomes and control efforts against schistosomiasis (both intestinal and urogenital Methods schistosomiasis), however, this information is very lim- Data for this review were identified and collected using ited in the public domain where they can be easily manual and electronic search strategies of published and unpublished sources. Electronic databases included PubMed, EMBASE and Global health. References of * Correspondence: [email protected] 1Department of Medical Parasitology and Entomology, School of Medicine, relevant articles were also screened. Manual identifica- Catholic University of Health and Allied Sciences, P.O. Box 1464, Mwanza, tion of unpublished literature sources, including unpub- Tanzania lished project surveys, university theses, conference 2Department of Environmental Health and Communicable Disease Control, School of Public Health|, College of Health Sciences, Makerere University, P.O. papers and public health organization reports was con- Box 7072, Kampala, Uganda ducted at The National Institute for Medical Research, Full list of author information is available at the end of the article © 2012 Mazigo et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Mazigo et al. Parasites & Vectors 2012, 5:274 Page 2 of 20 http://www.parasitesandvectors.com/content/5/1/274 Mwanza, Tanzania. The centre has a library established focal but the main extensive zones were found in the in the 1940’s with archives of information since 1850. south eastern and south western sides of Lake Victoria To identify relevant studies on schistosomiasis in and its island [19]. Schistosoma haematobium was widely Tanzania, the search initially began with the text string distributed and two extensive zones where noted to have “schistosom*” and a combination of the following words high transmission, namely the inland on the eastern and in permutations were used: “epidemiology”, “epidemi- south-eastern hinterland of Lake Victoria and lowland ology + Tanzania/Tanganyika”, “Schistosoma mansoni + zones on the eastern coast of the country [19]. Tanzania/Tanganyika”, and “Schistosoma haematobium The islands of Unguja and Pemba (Zanzibar islands) + Unguja + Pemba”, “schistosomiasis + Zanzibar”, were only endemic to Schistosoma haematobium and “Biomphalaria/Bulinus + Tanzania/Tanganyika”. Avail- the geographical distribution of the disease was largely able literature was categorized into population-based restricted to north-western and central areas of Unguja studies, clinical trials and basic malacology. Inclusion Island [3,6,7,19-22]. However, Pemba Island, was en- criteria were used with less stringency for the articles or demic for S. haematobium on the western, southern, papers that reported co-infections of schistosomiasis and central and northwest of the island [23-27]. Two trans- other tropical diseases in Tanzania. mission seasons of the disease were noted in the islands part of the country: the high season, accompanying The past and current epidemiology of schistosome the long rains which end in between June/July, and infections in Tanzania low transmission during the dry seasons [28]. It was Historical studies have revealed that both Schistosoma observed that S. mansoni was of little public health im- haematobium and Schistosoma mansoni have been en- portance in the two islands due to absence of its inter- demic for a long time in Tanzania. The first scientific re- mediate hosts: snails, the Biomphalaria species [3,7,19]. port of schistosomiasis in Tanzania can be traced back The construction of the hydroelectric dams and devel- to 1895 when Manson-Bahr published the first recorded opment of irrigations schemes in the late 1970s and case of intestinal bilharziasis [3,4]. The early studies in early 1980s to meet the needs of the growing population the Lake Victoria province (Tanzania mainland) by Cook for food production and water supply altered the trans- in 1905 at Kwimba identified and described the distribu- mission pattern of schistosomiasis in the country. These tion of S. mansoni and S. haematobium in the region water development projects were identified as the risk [3,5]. Over 50% of individuals examined had urogenital areas for transmission of schistosomiasis for communi- schistosomiasis [5] and S. mansoni was noted to be ties that lived and worked in areas surrounding the widespread on the southern and eastern shores of Lake hydroelectrical dams and irrigation schemes. The areas Victoria [5]. In 1903, urogenital schistosomiasis was created favourable environmental conditions for the noted to be prevalent among men by Petrie in Zanzibar snail intermediate hosts and the major impact was that [6,7]. However, it was not until 1925 that urogenital the disease was seen to spread to the areas that were not schistosomiasis epidemiology was described [3,7]. Other previously known to be endemic [12,29-35]. schistosomes species found in the country include Schis- Of the national population of 17.5 million people tosoma bovis, Schistosoma matheei and Schistosoma lei- (Tanzania mainland) in 1977, a total of 3.3 million (19%) peri which infect bovine species [8,9]. people were conservatively estimated to have constant Since the 1920s to date, large and small scale epi- exposure risk to schistosomiasis [36]. According to the demiological surveys have been conducted in the coun- estimates in national surveys of 1979–1980, 28.3% of the try to determine the distribution [10-12], intermediate population of mainland Tanzania (an approximate of 4.3 hosts [11-13], prevalences and intensity of both urogeni- million people) and 23.2% (approximate 3.9 million tal and intestinal schistosomiasis [14-18]. The results people) had urogenital and intestinal schistosomaisis, revealed that schistosomiasis was highly endemic respectively [36,37]. The nationwide survey conducted in throughout the country and the level of endemicity var- 1980 among schoolchildren (aged between 9 and 14 ied from region to region. The north-western regions, years old) showed that more than 50% had S. haemato- surrounding Lake Victoria, the northern, central, south- bium infection, the majority living in the endemic zones ern and south east of the country were identified to be of western and eastern parts of the country [3,36,37]. In highly endemic for S. mansoni [11,13,17],while the hin- 1990, for the projected population of 23.8 million terland areas of the country were highly endemic for S. people, the estimated national
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