RESEARCH Open Access Impact of climate variability on Plasmodium vivax

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