Ulrika Morris1, Weiping Xu2, Mwinyi I Msellem3, Alanna Schwartz4, Ali Abass3, Delér Shakely5, Jackie Cook6, Achuyt Bhattarai7, Max Petzold8, Bryan Greenhouse4, Abdullah S Ali3, Anders Björkman2, Gabrielle Fröberg9, Andreas Mårtensson10. 1. Malaria Research, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden. Electronic address: ulrika.morris@ki.se. 2. Malaria Research, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden. 3. Zanzibar Malaria Elimination Programme (ZAMEP), Ministry of Health, Zanzibar, Tanzania. 4. Department of Medicine, University of California San Francisco, CA, USA. 5. Malaria Research, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden; Department of Medicine, Kungälv Hospital, Kungälv, Sweden. 6. Malaria Research, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden; Zanzibar Malaria Elimination Programme (ZAMEP), Ministry of Health, Zanzibar, Tanzania. 7. Malaria Branch, Centers for Disease Control and Prevention, Atlanta, GA, USA. 8. Health Metrics at Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. 9. Department of Medicine, Solna, Karolinska Institutet, Stockholm, Sweden. 10. Malaria Research, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden; Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden; Centre for Clinical Research Sörmland, Uppsala University, Sweden.
Abstract
BACKGROUND: Improved understanding of the asymptomatic malaria parasite reservoir is a prerequisite to pursue malaria elimination efforts. We therefore characterised temporal trends and transporter polymorphisms in asymptomatic Plasmodium infections during the transition from high to low transmission in Zanzibar. METHODS: Healthy individuals participating in cross-sectional surveys conducted 2005-2013 were screened for asymptomatic malaria by PCR. Complexity/diversity of infection and transporter polymorphisms were assessed in Plasmodium falciparum positive samples. Symptomatic samples were included for comparison of polymorphisms in 2013. RESULTS: PCR-determined parasite prevalence declined from 21.1% (CI95% 17.4-24.9) to 2.3% (CI95% 1.7-2.9) from 2005 to 2013. P. falciparum remained the predominant species; prevalence was highest in children and young adults aged 5-25 years. Parasite densities and complexity of infection, but not population genetic diversity of P. falciparum, decreased from 2005-2009. pfcrt 76T (99.2-64.7%, p < 0.001) and pfmdr1 86Y frequencies (89.4-66.7%, p = 0.03) decreased over time. Pfmdr1 (a.a.86,184,1246) YYY and YYD haplotypes were more frequent in asymptomatic than symptomatic infections in 2013 (p < 0.001). CONCLUSIONS: There is a declining, albeit persistent, reservoir of parasites present at low-densities in asymptomatic individuals in Zanzibar. This study revealed important characteristics of the remaining parasite population, including intriguing temporal trends in molecular markers associated with antimalarial resistance, which need to be further investigated.
BACKGROUND: Improved understanding of the asymptomatic malaria parasite reservoir is a prerequisite to pursue malaria elimination efforts. We therefore characterised temporal trends and transporter polymorphisms in asymptomatic Plasmodium infections during the transition from high to low transmission in Zanzibar. METHODS: Healthy individuals participating in cross-sectional surveys conducted 2005-2013 were screened for asymptomatic malaria by PCR. Complexity/diversity of infection and transporter polymorphisms were assessed in Plasmodium falciparum positive samples. Symptomatic samples were included for comparison of polymorphisms in 2013. RESULTS: PCR-determined parasite prevalence declined from 21.1% (CI95% 17.4-24.9) to 2.3% (CI95% 1.7-2.9) from 2005 to 2013. P. falciparum remained the predominant species; prevalence was highest in children and young adults aged 5-25 years. Parasite densities and complexity of infection, but not population genetic diversity of P. falciparum, decreased from 2005-2009. pfcrt 76T (99.2-64.7%, p < 0.001) and pfmdr1 86Y frequencies (89.4-66.7%, p = 0.03) decreased over time. Pfmdr1 (a.a.86,184,1246) YYY and YYD haplotypes were more frequent in asymptomatic than symptomatic infections in 2013 (p < 0.001). CONCLUSIONS: There is a declining, albeit persistent, reservoir of parasites present at low-densities in asymptomatic individuals in Zanzibar. This study revealed important characteristics of the remaining parasite population, including intriguing temporal trends in molecular markers associated with antimalarial resistance, which need to be further investigated.
Authors: Ulrika Morris; Mwinyi Khamis; Berit Aydin-Schmidt; Ali K Abass; Mwinyi I Msellem; Majda H Nassor; Iveth J González; Andreas Mårtensson; Abdullah S Ali; Anders Björkman; Jackie Cook Journal: Malar J Date: 2015-05-17 Impact factor: 2.979
Authors: Berit Aydin-Schmidt; Ulrika Morris; Xavier C Ding; Irina Jovel; Mwinyi I Msellem; Daniel Bergman; Atiqul Islam; Abdullah S Ali; Spencer Polley; Iveth J Gonzalez; Andreas Mårtensson; Anders Björkman Journal: PLoS One Date: 2017-01-17 Impact factor: 3.240
Authors: Lucy C Okell; Lisa Malene Reiter; Lene Sandø Ebbe; Vito Baraka; Donal Bisanzio; Oliver J Watson; Adam Bennett; Robert Verity; Peter Gething; Cally Roper; Michael Alifrangis Journal: BMJ Glob Health Date: 2018-10-19
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Authors: Deus S Ishengoma; Celine I Mandara; Filbert Francis; Eldin Talundzic; Naomi W Lucchi; Billy Ngasala; Abdunoor M Kabanywanyi; Muhidin K Mahende; Erasmus Kamugisha; Reginald A Kavishe; Florida Muro; Ally Mohamed; Renata Mandike; Sigsbert Mkude; Frank Chacky; Lynn Paxton; George Greer; Chonge A Kitojo; Ritha Njau; Troy Martin; Meera Venkatesan; Marian Warsame; Eric S Halsey; Venkatachalam Udhayakumar Journal: Malar J Date: 2019-03-21 Impact factor: 2.979