Spatiotemporal patterns of malaria incidence in northern Thailand.
We present a detailed analysis of long-term time series of malaria incidence in northern Thailand. Positive cases for Plasmodium falciparum and P. vivax have been recorded monthly from 1977-2002 at 13 provinces in the region. Time series statistical methods are used to examine the long-term trends and seasonal dynamics of malaria incidence at regional and provincial scales. Both malarial types are declining throughout the region, except in the two provinces that share a large border with Myanmar. The rate of decline in P. vivax has decreased across the region since the end of the 1980s, and this may be a signal of developing resistance or changing vector potential. Both species display a two-peak annual seasonality that may be attributed to patterns of vector occurrence, farming practice and migration of individuals across international borders. In a number of provinces, the importance of the first seasonal peak has grown in recent years, possibly owing to increases in vector densities. The medium-term fluctuations of both species exhibit a clear spatial organisation. There is some evidence of a subtle close to 4-year super annual cycle in P. falciparum, which we suggest is driven by extrinsic factors relating to the climate of the region.
Childs
D Z
DZ
Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK. d.childs@sheffield.ac.uk
Cattadori
I M
IM
Suwonkerd
W
W
Prajakwong
S
S
Boots
M
M
D006801:Humans; D015994:Incidence; D016778:Malaria, Falciparum / Q000453:epidemiology*; D016780:Malaria, Vivax / Q000453:epidemiology*; D012621:Seasons; D013029:Space-Time Clustering; D013785:Thailand / Q000453:epidemiology