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Assessing the Impact of Meteorological Factors on Malaria Patients in Demilitarized Zones in Republic of Korea

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Assessing the Impact of Meteorological Factors on Malaria Patients in Demilitarized Zones in Republic of Korea

Se-Min Hwang et al. Infect Dis Poverty.

Abstract

Background: The trend of military patients becoming infected with vivax malaria reemerged in the Republic of Korea (ROK) in 1993. The common explanation has been that infective Anopheles mosquitoes from the Democratic People's Republic of Korea have invaded Republic of Korea's demilitarized zone (DMZ). The aim of this study was to verify the relationship between meteorological factors and the number of malaria patients in the military in this region.

Methods: The authors estimated the effects of meteorological factors on vivax malaria patients from the military based on the monthly number of malaria cases between 2006 and 2011. Temperature, precipitation, snow depth, wind velocity, relative humidity, duration of sunshine, and cloud cover were selected as the meteorological factors to be studied. A systematic pattern in the spatial distribution of malaria cases was assessed using the Moran's Index. Granger causality tests and cross-correlation coefficients were used to evaluate the relationship between meteorological factors and malaria patients in the military.

Results: Spatial analysis revealed significant clusters of malaria patients in the military in Republic of Korea in 2011 (Moran's I = 0.136, p-value = 0.026). In the six years investigated, the number of malaria patients in the military in Paju decreased, but the number of malaria patients in the military in Hwacheon and Chuncheon increased. Monthly average, maximum and minimum temperatures; wind velocity; and relative humidity were found to be predicting factors of malaria in patients in the military in Paju. In contrast, wind velocity alone was not able to predict malaria in Hwacheon and Chuncheon, however, precipitation and cloud cover were able to predict malaria in Hwacheon and Chuncheon.

Conclusions: This study demonstrated that the number of malaria patients in the military is correlated with meteorological factors. The variation in occurrence of malaria cases was principally attributed to differences in meteorological factors by regions of Republic of Korea.

Figures

Fig. 1
Fig. 1
Geographical distribution of malaria patients in South Korea from 2006 to 2011 ((a): total cases, data from the KCDCs; (b): malaria patients in the military, data from the AFMC). B*: Total military malaria cases were 321 in 2006, and the distribution of military malaria cases (N ≧ 10) in 2006 is: 108 (33.6%) in Paju, Gyeonggi-do; 82 (25.6%) in Dongducheon, Gyeonggi-do; 56 (17.5%) in Cheorwon, Gangwon-do; 15 (4.7%) in Hwacheon and Chuncheon, Gangwon-do; 13 (4.1%) in Incheon; and 11 (3.4%) in Inje, Gangwon-do. The case number reduced to 148 cases in 2011 and the distribution of military malaria cases (N ≧ 10) in 2011 is: 39 (26.4%) in Hwacheon and Chuncheon, Gangwon-do; 39 (26.4%) in Cheorwon, Gangwon-do; 35 (23.7%) in Dongducheon, Gyeonggi-do; 29 (19.6%) in Paju, Gyeonggi –do; 4 (2.7%) in Inje, Gangwon-do; and 4 (2.7%) in Incheon
Fig. 2
Fig. 2
Spatial distribution of malaria patients in South Korea. a: civilian malaria patients, 2006; (b): civilian malaria patients, 2011; (c): malaria patients in the military, 2006; (d): malaria patients in the military, 2011. * Cluster pattern of malaria patients in the military was estimated using the Moran’s Index (c, d)
Fig. 3
Fig. 3
Times-series plots for monthly malaria patients in the military, using wind velocity as a variable (Jan 2006 – Dec 2011). *(a): Paju, (b): Hwacheon and Chuncheon. av_temp: average temperature, wind_v: wind velocity
Fig. 4
Fig. 4
Dynamics of malaria outbreaks in the military: comparison of Paju and the Chuncheon weather station area. a: malaria patients in the military, 2006. b: malaria patients in the military, 2011. (a) Kaesong Industrial Complex began operating at the beginning of 2007. As a result, there might have been an influx of mosquitos carrying P. vivax malaria from north DMZ to Paju. (b), (d) Paju had been heavily influenced by northeasterly wind from 2006 to 2007, but its effects weakened between 2008 and 2011. As a result, transmission of P. vivax malaria by mosquitos from north DMZ to Paju might be contained. (c), (e) As Bukhan River might be a mosquito larvae reservoir, this might contribute to an increase in the number of malaria patients in the military around this area: malaria patients decreased in Cheorwon (c), and Inje (e), but otherwise malaria patients in the military increased in the Chuncheon weather station area (Hwacheon and Chuncheon)

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