title: Impact of climate variability on Plasmodium vivax and Plasmodium falciparum malaria in Yunnan Province, China.
abstract: BACKGROUND
  Malaria remains a public health problem in the remote and poor area of Yunnan Province, China. Yunnan faces an increasing risk of imported malaria infections from Mekong river neighboring countries. This study aimed to identify the high risk area of malaria transmission in Yunnan Province, and to estimate the effects of climatic variability on the transmission of Plasmodium vivax and Plasmodium falciparum in the identified area.
  
  
  METHODS
  We identified spatial clusters of malaria cases using spatial cluster analysis at a county level in Yunnan Province, 2005-2010, and estimated the weekly effects of climatic factors on P. vivax and P. falciparum based on a dataset of daily malaria cases and climatic variables. A distributed lag nonlinear model was used to estimate the impact of temperature, relative humidity and rainfall up to 10-week lags on both types of malaria parasite after adjusting for seasonal and long-term effects.
  
  
  RESULTS
  The primary cluster area was identified along the China-Myanmar border in western Yunnan. A 1°C increase in minimum temperature was associated with a lag 4 to 9 weeks relative risk (RR), with the highest effect at lag 7 weeks for P. vivax (RR = 1.03; 95% CI, 1.01, 1.05) and 6 weeks for P. falciparum (RR = 1.07; 95% CI, 1.04, 1.11); a 10-mm increment in rainfall was associated with RRs of lags 2-4 weeks and 9-10 weeks, with the highest effect at 3 weeks for both P. vivax (RR = 1.03; 95% CI, 1.01, 1.04) and P. falciparum (RR = 1.04; 95% CI, 1.01, 1.06); and the RRs with a 10% rise in relative humidity were significant from lag 3 to 8 weeks with the highest RR of 1.24 (95% CI, 1.10, 1.41) for P. vivax at 5-week lag.
  
  
  CONCLUSIONS
  Our findings suggest that the China-Myanmar border is a high risk area for malaria transmission. Climatic factors appeared to be among major determinants of malaria transmission in this area. The estimated lag effects for the association between temperature and malaria are consistent with the life cycles of both mosquito vector and malaria parasite. These findings will be useful for malaria surveillance-response systems in the Mekong river region.
authors.affiliation: School of Public Health and Social Work, Institute of Health and Biomedical Innovation, Queensland University of Technology, Victoria Park Rd, Kelvin Grove, Brisbane, QLD 4059, Australia. 7yanbi@gmail.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Bi
authors.forename: Weiwei
authors.initials: W
authors.lastname: Yu
authors.forename: Wenbiao
authors.initials: W
authors.lastname: Hu
authors.forename: Hualiang
authors.initials: H
authors.lastname: Lin
authors.forename: Yuming
authors.initials: Y
authors.lastname: Guo
authors.forename: Xiao-Nong
authors.initials: XN
authors.lastname: Zhou
authors.forename: Shilu
authors.initials: S
authors.lastname: Tong
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D057231:Climate Change; D006801:Humans; D006813:Humidity; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000469:parasitology; D016780:Malaria, Vivax / Q000453:epidemiology* / Q000469:parasitology; D010963:Plasmodium falciparum / Q000502:physiology*; D010966:Plasmodium vivax / Q000502:physiology*; D012307:Risk Factors; D013696:Temperature; D013997:Time Factors