title: Epidemiology of malaria in a village in the Rufiji River Delta, Tanzania: declining transmission over 25 years revealed by different parasitological metrics.
abstract: BACKGROUND
  Assessments of the epidemiology of malaria over time are needed to understand changes in transmission and guide control and elimination strategies.
  
  
  METHODS
  A longitudinal population study was established in 1985 in Nyamisati village in the Rufiji River Delta, Tanzania. A physician and research team lived in the village 1984-2000. Parasite prevalence by microscopy and two PCR methods, spleen rates and haemoglobin levels were measured in repeated cross-sectional surveys between 1985 and 2010. Passive surveillance of malaria cases was maintained until end 1999. Bed nets were distributed after the surveys 1993, 1999 and 2010.
  
  
  RESULTS
  In 1985, overall parasite prevalence by microscopy was 70% (90% in children ages two to nine years). The prevalence decreased gradually by microscopy (38.9% 1994, 26.7% 1999) and msp2-PCR (58.7% 1994, 44.8% 1999), whereas real-time PCR prevalence remained higher throughout the 1990s (69.4% 1994, 64.8% 1999). In 2010, parasite prevalence was 17.8% by real-time PCR and 16.3% by msp2-PCR, and estimated to 4.8% by microscopy. Spleen rates in children ages two to nine years decreased earlier than parasite prevalence, from >75 to 42% in the 1980s, to nil during the 1990s. The prevalence of severe and moderate anaemia decreased from 41.1 to 13.1%. No deaths at the time of acute malaria were recorded when the research team lived in the village.
  
  
  CONCLUSIONS
  A marked decline in malaria transmission was observed over 25 years. The decrease was detected after the arrival of the research team and continued gradually both before and after distribution of bed nets. Spleen rates and microscopy identified early changes when transmission was still intense, whereas real-time PCR was a more sensitive metric when transmission was reduced. The study provides historical data on malaria within a closely monitored rural village and contributes to the understanding of changing epidemiology in sub-Saharan Africa.
authors.affiliation: Infectious Diseases Unit, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden. anna.farnert@ki.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Färnert
authors.forename: Victor
authors.initials: V
authors.lastname: Yman
authors.forename: Manijeh Vafa
authors.initials: MV
authors.lastname: Homann
authors.forename: Grace
authors.initials: G
authors.lastname: Wandell
authors.forename: Leah
authors.initials: L
authors.lastname: Mhoja
authors.forename: Marita
authors.initials: M
authors.lastname: Johansson
authors.forename: Salome
authors.initials: S
authors.lastname: Jesaja
authors.forename: Johanna
authors.initials: J
authors.lastname: Sandlund
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Tanabe
authors.forename: Ulf
authors.initials: U
authors.lastname: Hammar
authors.forename: Matteo
authors.initials: M
authors.lastname: Bottai
authors.forename: Zulfiqarali G
authors.initials: ZG
authors.lastname: Premji
authors.forename: Anders
authors.initials: A
authors.lastname: Björkman
authors.forename: Ingegerd
authors.initials: I
authors.lastname: Rooth
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008288:Malaria / Q000453:epidemiology* / Q000635:transmission*; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D010961:Plasmodium / Q000302:isolation & purification; D015995:Prevalence; D060888:Real-Time Polymerase Chain Reaction; D013154:Spleen / Q000473:pathology; D013636:Tanzania / Q000453:epidemiology; D055815:Young Adult
chemical_list: D006454:Hemoglobins