title: Trichuris trichiura infection and its relation to environmental factors in Mbeya region, Tanzania: A cross-sectional, population-based study.
abstract: BACKGROUND
  The intestinal nematode Trichuris trichiura is among the most common causes of human infectious disease worldwide. As for other soil-transmitted nematodes, its reproductive success and thus prevalence and intensity of infection in a given area strongly depend on environmental conditions. Characterization of the influence of environmental factors can therefore aid to identify infection hot spots for targeted mass treatment.
  
  
  METHODS
  We analyzed data from a cross-sectional survey including 6234 participants from nine distinct study sites in Mbeya region, Tanzania. A geographic information system was used to combine remotely sensed and individual data, which were analyzed using uni- and multivariable Poisson regression. Household clustering was accounted for and when necessary, fractional polynomials were used to capture non-linear relationships between T. trichiura infection prevalence and environmental variables.
  
  
  RESULTS
  T. trichiura infection was restricted to the Kyela site, close to Lake Nyasa with only very few cases in the other eight sites. The prevalence of T. trichiura infection in Kyela was 26.6% (95% confidence interval (CI) 23.9 to 29.6%). Multivariable models revealed a positive association of infection with denser vegetation (prevalence ratio (PR) per 0.1 EVI units = 2.12, CI 1.28 to 3.50) and inverse associations with rainfall (PR per 100 mm = 0.54, CI 0.44 to 0.67) and elevation (PR per meter = 0.89, CI 0.86 to 0.93) while adjusting for age and previous worm treatment. Slope of the terrain was modelled non-linearly and also showed a positive association with T. trichiura infection (p-value p<0.001).
  
  
  CONCLUSIONS
  Higher prevalences of T. trichiura infection were only found in Kyela, a study site characterized by denser vegetation, high rainfall, low elevation and flat terrain. But even within this site, we found significant influences of vegetation density, rainfall, elevation and slope on T. trichiura infection. The inverse association of rainfall with infection in Kyela is likely due to the fact, that rainfall in this site is beyond the optimum conditions for egg development. Our findings demonstrate that use of remotely sensed environmental data can aid to predict high-risk areas for targeted helminth control.
authors.affiliation: Institute for Medical Informatics, Biometry and Epidemiology, Ludwig-Maximilians-University, Munich, Germany.|Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.
authors.forename: Kirsi M
authors.identifier: http://orcid.org/0000-0002-7740-4076
authors.initials: KM
authors.lastname: Manz
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.|NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Petra
authors.initials: P
authors.lastname: Clowes
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.|NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.|German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Inge
authors.initials: I
authors.lastname: Kroidl
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Dickens O
authors.initials: DO
authors.lastname: Kowuor
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.|German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Geldmacher
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Nyanda E
authors.initials: NE
authors.lastname: Ntinginya
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Leonard
authors.initials: L
authors.lastname: Maboko
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.|NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.|German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hoelscher
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.|German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Elmar
authors.initials: E
authors.lastname: Saathoff
mesh_terms: D000293:Adolescent; D000818:Animals; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D012307:Risk Factors; D013636:Tanzania / Q000453:epidemiology; D014257:Trichuriasis / Q000453:epidemiology*; D014258:Trichuris / Q000472:pathogenicity*