Study On The Ecologic Factors For Malaria Re-emergence In The Areas Along The Yellow River And Huai River

Objectives To study the major ecologic factors influenced the re-emergence of malaria in the areas along the Yellow River and Huai River by the analysis on the relationship between the re-emergence of malaria incidence and the changes in ecologic factors.Methods1. The analysis of the effects on malaria transmission made by meteorological factors:â‘ Delineated the curves of malaria annual incidence, average annual temperature, average annual rainfall and average annual relative humidity, to explain the annual trends of these factors changes and its relationship with the re-emergence of malaria.â‘¡Considering the cycle of growth and deve-lopment of plasmodium vivax and anophelines, we conducted the data processing and derived the new parameter as follow: T_mean01, T_mean012, R_mean01, R_mean012, M_mean01, M_mean012. Use Spearman rank correlation to analyze the relationship between these meteorological factors and malaria incidence.â‘¢Use multiple regression, to seek the more effective meteorological factors.â‘£Base on the results of the Spearman rank correlation and multiple regression analysis, usecurve fitting and trend analysis to explain these factors influencing malaria transmission.2. The analysis of relationship between LUCC and malaria transmission:â‘ The data of land useand land cover (LUCC) in Huaiyuan, Yongcheng and Tongbai change extract from images of remote sensing by Resources and Environment Science, Chinese Academy of Sciences Data Center.â‘¡Analysis of the environment changes in these periods(1980s-1995,1995-2000), were conducted by counting the areas and the proportion of each type of LUCC in 1980s, 1995 and 2000. The correlation coefficients of malaria incidences and these environmental changes were calculated with SPSS 11.5.3. Analysis of the risk range of malaria transimission according to the distribution of water-body:â‘ Collected the geographic information of the malaria cases with global position system locator.â‘¡Use the soft ware of Mapsource to conduct the data processing and establish the database in excel. Then we conducted spatial analysis with ArcGIS 9.2 to calculate the distance between the houses of malara cases and the water-body.â‘¢To analyze the characters of the distribution of malaria cases based on the results of statistcs analysis of the distance calculated above.â‘£Grouping all the residents in the village according to the characters of the distribution of malaria cases, useχ² test to analyze the risk of malaria transimission.Results1. The curves of malaria annual incidence, average annual temperature, average annual rainfall and average annual relative humidity show that the annual temperature, average annual rainfall may have close relationship with malaria annual incidence. Then the results of correlation show that the average monthly temperature and rainfall are top two factors which had positive correlation to monthly malaria incidence, the correlation coefficients are 0.501 and 0.304(P<0.01) separately. The multiple regression showed that 75.3% changes of monthly malaria incidence contributed to the average monthly temperature (T_mean) , the average temperature of last two months(T_mean01) and the average rainfall of current month (R_mean).In the recent 15 years, the annual average temperature was increased year by year in Yellow River and Huaihe River basins. Especially in April and November, the monthly average temperature rose significantly and the tendency rate separately is 0.17 and 0.15. Both the number of malaria cases and malaria incidence in May and November had been increased significantly since 2000. The proportion of malaria cases in the two months contribute to the annual cases once went up to 5.68% and 4.97%.These findings indicated that the temperature growing higher in April and November prolonged the malaria transmission season(from June-October to May-November) .The rainfall was increased in these years too. The monthly mean rainfall increased significantly in July and August, the tendency rate separately is 9.99 and 8.45.The number of malaria cases in July and August had been increased since 2000 and also in the proportion of malaria cases in the two months contribute to the annual case. These indicated that the increasing of rainfall in July and August enhanced the malaria transmission in the two months.2. The analysis of Land use and cover change (LUCC) showed: the LUCC is significant in Tongbai county in the period from 1980s to 1995 and from 1995 to 2000. The rate of land use changes was separately 3265.79% and -97.03% in the farmland, while -90.42% and 950.30% in paddy field. In the same time, the analysis of the annual malaria incidence showed: the annual malaria incidence increased rapidly in 1996(annual malaria incidence was 385.41/100 000 and the number of malaria cases was 1 620). However, the analysis of LUCC in Huaiyuan county and Yongcheng county showed that no significant changes could be found. So we need to enlarge the capacity of investigation to make sure whether the large scale changes in the environment, such as LUCC, played an important role in malaria re-emergence. That attribute to the resolution of the images procured by the remote sensing.3. The analysis on the geographic information of 357 malaria cases location and around water body in 113 villages showed that the most of malaria cases (74%) in the study are inhabited in the extent of 60 m near the water body, the risk rate of people live there attacked by malaria was higher than others(OR=1 .6, 95%CI (1.042,2.463), P<0.05).Conclusion:1. The temperature and rainfall are two major factors which influenced the malaria re-emerging in Yellow River and Huaihe River basins. The average monthly temperature increased in April and November result in the extension of malaria transmission season, while the enhancing of malaria transmission in July and August account for the raising of rainfall. The malaria transmission season had been prolonged from June-October to May-November.2. LUCC did play an important role in malaria transmission, but we could do limited analysis only in the county level because of the resolution of images and the capacity of sample. So we could not make conclusion that LUCC played an important effect on malaria re-emergence in these area confidently.3. There were no significant results of large scales analysis in environment changes, but in the smaller scale analysis we got one. The spatial characters of water-body influenced the distribution of malaria cases. The extent of 60 m around water-body is the risk area of malaria and the key area of malaria sources of infection.