title: Associations between Season and Gametocyte Dynamics in Chronic Plasmodium falciparum Infections.
abstract: BACKGROUND
  In a markedly seasonal malaria setting, the transition from the transmission-free dry season to the transmission season depends on the resurgence of the mosquito population following the start of annual rains. The sudden onset of malaria outbreaks at the start of the transmission season suggests that parasites persist during the dry season and respond to either the reappearance of vectors, or correlated events, by increasing the production of transmission stages. Here, we investigate whether Plasmodium falciparum gametocyte density and the correlation between gametocyte density and parasite density show seasonal variation in chronic (largely asymptomatic) carriers in eastern Sudan.
  
  
  METHODS
  We recruited and treated 123 malaria patients in the transmission season 2001. We then followed them monthly during four distinct consecutive epidemiological seasons: transmission season 1, transmission-free season, pre-clinical period, and transmission season 2. In samples collected from 25 participants who fulfilled the selection criteria of the current analysis, we used quantitative PCR (qPCR) and RT-qPCR to quantify parasite and gametocyte densities, respectively.
  
  
  CONCLUSIONS
  We observed a significant increase in gametocyte density and a significantly steeper positive correlation between gametocyte density and total parasite density during the pre-clinical period compared to the preceding transmission-free season. However, there was no corresponding increase in the density or prevalence of total parasites or gametocyte prevalence. The increase in gametocyte production during the pre-clinical period supports the hypothesis that P. falciparum may respond to environmental cues, such as mosquito biting, to modulate its transmission strategy. Thus, seasonal changes may be important to ignite transmission in unstable-malaria settings.
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Oman.|Department of Molecular Epidemiology, Tropical Medicine Research Institute, National Centre for Research, Khartoum, Sudan.
authors.forename: Amal A H
authors.initials: AA
authors.lastname: Gadalla
authors.affiliation: Institutes of Evolution, Immunology and Infection Research, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Petra
authors.initials: P
authors.lastname: Schneider
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Churcher
authors.affiliation: Medicinal and Aromatic Plants Research Institute and Traditional Medicine, National Centre for Research, Khartoum, Sudan.
authors.forename: Elkhansaa
authors.initials: E
authors.lastname: Nassir
authors.affiliation: Department of Biology, Faculty of Science, University of Hail, Baqaa, Kingdom of Saudi Arabia.
authors.forename: Abdel-Muhsin A
authors.initials: AA
authors.lastname: Abdel-Muhsin
authors.affiliation: Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Lisa C
authors.initials: LC
authors.lastname: Ranford-Cartwright
authors.affiliation: Institutes of Evolution, Immunology and Infection Research, University of Edinburgh, Edinburgh, United Kingdom.|Centre for Immunity, Infection & Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Reece
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Oman.|Institutes of Evolution, Immunology and Infection Research, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Hamza A
authors.initials: HA
authors.lastname: Babiker
mesh_terms: D016054:DNA, Protozoan / Q000032:analysis; D005854:Germ Cells / Q000254:growth & development*; D006801:Humans; D016778:Malaria, Falciparum / Q000469:parasitology / Q000635:transmission*; D008297:Male; D010963:Plasmodium falciparum / Q000235:genetics / Q000502:physiology*; D012621:Seasons; D013397:Sudan
chemical_list: D016054:DNA, Protozoan