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      A Search for Snail-Related Answers to Explain Differences in Response of Schistosoma mansoni to Praziquantel Treatment among Responding and Persistent Hotspot Villages along the Kenyan Shore of Lake Victoria

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          Abstract.

          Following a 4-year annual praziquantel (PZQ) treatment campaign, the resulting prevalence of Schistosoma mansoni was seen to differ among individual villages along the Kenyan shore of Lake Victoria. We have investigated possible inherent differences in snail-related aspects of transmission among such 10 villages, including six persistent hotspot (PHS) villages (≤ 30% reduction in prevalence following repeated treatments) located along the west-facing shore of the lake and four PZQ-responding (RESP) villages (> 30% prevalence reduction following repeated treatment) along the Winam Gulf. When taking into account all sampling sites, times, and water hyacinth presence/absence, shoreline-associated Biomphalaria sudanica from PHS and RESP villages did not differ in relative abundance or prevalence of S. mansoni infection. Water hyacinth intrusions were associated with increased B. sudanica abundance. The deeper water snail Biomphalaria choanomphala was significantly more abundant in the PHS villages, and prevalence of S. mansoni among villages both before and after control was positively correlated with B. choanomphala abundance. Worm recoveries from sentinel mice did not differ between PHS and RESP villages, and abundance of non-schistosome trematode species was not associated with S. mansoni abundance. Biomphalaria choanomphala provides an alternative, deepwater mode of transmission that may favor greater persistence of S. mansoni in PHS villages. As we found evidence for ongoing S. mansoni transmission in all 10 villages, we conclude that conditions conducive for transmission and reinfection occur ubiquitously. This argues for an integrated, basin-wide plan for schistosomiasis control to counteract rapid reinfections facilitated by large snail populations and movements of infected people around the lake.

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          Most cited references 49

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          Human schistosomiasis.

          Human schistosomiasis--or bilharzia--is a parasitic disease caused by trematode flukes of the genus Schistosoma. By conservative estimates, at least 230 million people worldwide are infected with Schistosoma spp. Adult schistosome worms colonise human blood vessels for years, successfully evading the immune system while excreting hundreds to thousands of eggs daily, which must either leave the body in excreta or become trapped in nearby tissues. Trapped eggs induce a distinct immune-mediated granulomatous response that causes local and systemic pathological effects ranging from anaemia, growth stunting, impaired cognition, and decreased physical fitness, to organ-specific effects such as severe hepatosplenism, periportal fibrosis with portal hypertension, and urogenital inflammation and scarring. At present, preventive public health measures in endemic regions consist of treatment once every 1 or 2 years with the isoquinolinone drug, praziquantel, to suppress morbidity. In some locations, elimination of transmission is now the goal; however, more sensitive diagnostics are needed in both the field and clinics, and integrated environmental and health-care management will be needed to ensure elimination. Copyright © 2014 Elsevier Ltd. All rights reserved.
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            Scaling regression inputs by dividing by two standard deviations.

             Andrew Gelman (2008)
            Interpretation of regression coefficients is sensitive to the scale of the inputs. One method often used to place input variables on a common scale is to divide each numeric variable by its standard deviation. Here we propose dividing each numeric variable by two times its standard deviation, so that the generic comparison is with inputs equal to the mean +/-1 standard deviation. The resulting coefficients are then directly comparable for untransformed binary predictors. We have implemented the procedure as a function in R. We illustrate the method with two simple analyses that are typical of applied modeling: a linear regression of data from the National Election Study and a multilevel logistic regression of data on the prevalence of rodents in New York City apartments. We recommend our rescaling as a default option--an improvement upon the usual approach of including variables in whatever way they are coded in the data file--so that the magnitudes of coefficients can be directly compared as a matter of routine statistical practice. (c) 2007 John Wiley & Sons, Ltd.
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              Neglected Tropical Diseases in Sub-Saharan Africa: Review of Their Prevalence, Distribution, and Disease Burden

              The neglected tropical diseases (NTDs) are the most common conditions affecting the poorest 500 million people living in sub-Saharan Africa (SSA), and together produce a burden of disease that may be equivalent to up to one-half of SSA's malaria disease burden and more than double that caused by tuberculosis. Approximately 85% of the NTD disease burden results from helminth infections. Hookworm infection occurs in almost half of SSA's poorest people, including 40–50 million school-aged children and 7 million pregnant women in whom it is a leading cause of anemia. Schistosomiasis is the second most prevalent NTD after hookworm (192 million cases), accounting for 93% of the world's number of cases and possibly associated with increased horizontal transmission of HIV/AIDS. Lymphatic filariasis (46–51 million cases) and onchocerciasis (37 million cases) are also widespread in SSA, each disease representing a significant cause of disability and reduction in the region's agricultural productivity. There is a dearth of information on Africa's non-helminth NTDs. The protozoan infections, human African trypanosomiasis and visceral leishmaniasis, affect almost 100,000 people, primarily in areas of conflict in SSA where they cause high mortality, and where trachoma is the most prevalent bacterial NTD (30 million cases). However, there are little or no data on some very important protozoan infections, e.g., amebiasis and toxoplasmosis; bacterial infections, e.g., typhoid fever and non-typhoidal salmonellosis, the tick-borne bacterial zoonoses, and non-tuberculosis mycobaterial infections; and arboviral infections. Thus, the overall burden of Africa's NTDs may be severely underestimated. A full assessment is an important step for disease control priorities, particularly in Nigeria and the Democratic Republic of Congo, where the greatest number of NTDs may occur.
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                Author and article information

                Journal
                Am J Trop Med Hyg
                Am. J. Trop. Med. Hyg
                tpmd
                tropmed
                The American Journal of Tropical Medicine and Hygiene
                The American Society of Tropical Medicine and Hygiene
                0002-9637
                1476-1645
                July 2019
                03 June 2019
                03 June 2019
                : 101
                : 1
                : 65-77
                Affiliations
                [1 ]Centre for Biotechnology Research and Development, Kenya Medical Research Institute, Nairobi, Kenya;
                [2 ]School of Biological Sciences, College of Biological and Physical Sciences, University of Nairobi, Nairobi, Kenya;
                [3 ]Department of Biology, Center for Evolutionary and Theoretical Immunology, Museum of Southwestern Biology, Parasitology Division, University of New Mexico, Albuquerque, New Mexico;
                [4 ]Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, Oregon;
                [5 ]Influenza Surveillance Program, Centers for Disease Control and Prevention, Nairobi, Kenya;
                [6 ]Department of Basic Medical Sciences, Western University of Health Sciences, Lebanon, Oregon
                Author notes
                [* ]Address correspondence to Martin W. Mutuku, Centre for Biotechnology Research and Development, Kenya Medical Research Institute, P.O. Box 54840-00200, Nairobi, Kenya. E-mail: mmutuku@ 123456kemri.org

                Financial support: This study was supported by the University of Georgia Research Foundation Inc., which was funded by the Bill & Melinda Gates Foundation for the SCORE project and the National Institutes of Health grants numbered R37AI101438, 1R01AI141862, and P30GM110907, and The Fogarty International Center and National Institute of Mental Health, NIH award number D43 TW010543.

                Authors’ addresses: Martin W. Mutuku, Centre for Biotechnology Research and Development, Kenya Medical Research Institute, Nairobi, Kenya, and School of Biological Sciences, College of Biological and Physical Sciences, University of Nairobi, Nairobi, Kenya, E-mails: mmutuku@ 123456kemri.org or mwmutuku81@ 123456gmail.com . Martina R. Laidemitt, Bishoy Kamel, and Eric S. Loker, Department of Biology, Center for Evolutionary and Theoretical Immunology, Museum of Southwestern Biology, Parasitology Division, University of New Mexico, Albuquerque, NM, E-mails: mlaidemitt@ 123456unm.edu , bishoyh@ 123456unm.edu , and esloker@ 123456unm.edu . Brianna R. Beechler, Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR, E-mail: breebeechler@ 123456gmail.com . Ibrahim N. Mwangi, Eric L. Agola, and Gerald M. Mkoji, Centre for Biotechnology Research and Development, Kenya Medical Research Institute, Nairobi, Kenya, E-mails: indungu@ 123456kemri.org , elelo@ 123456kemri.org , and gmkoji5@ 123456gmail.com . Fredrick O. Otiato, Influenza Surveillance Program, Centers for Disease Control and Prevention, Nairobi, Kenya, E-mail: frede516@ 123456gmail.com . Horace Ochanda, School of Biological Sciences, College of Biological and Physical Sciences, University of Nairobi, Nairobi, Kenya, E-mail: hochanda@ 123456uonbi.ac.ke . Michelle L. Steinauer, Department of Basic Medical Sciences, Western University of Health Sciences, Lebanon, OR, E-mail: msteinauer@ 123456westernu.edu .

                Article
                tpmd190089
                10.4269/ajtmh.19-0089
                6609173
                31162012
                © The American Society of Tropical Medicine and Hygiene

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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                Pages: 13
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