Risk Assessment For Malaria Transmission In The Border Area Of Yunnan Province

Since 2010, China has initiated the National Malaria Elimination Action Plan, which aims to eliminate indigenous malaria except for border areas by 2015, and completely eliminate it nationwide by 2020. By the end of December 2014, obvious achievements in controlling the locally-transmitted malaria were made except for the counties along the border of China-Myanmar, and Motuo County of Tibetan Autonomous Region. The malaria prevalence of Yunnan Province is particularly high and was one of the hardest and most important areas for malaria control and elimination due to its heterogeneity and complexity. After integrated control interventions, the indigenous cases were sharply reduced and the scale narrowed, but in five identified Myanmar communities along the China-Myanmar border, which harbored a heavy burden of malaria and the healthcare system is fragile. This infection source combined with frequent population movement and suitable conditions for malaria transmission, which will bring out high risk for the outbreak of secondary cases induced by imported cases. In addition, the confirmed emergence of artemisinin resistance in Great Mekong Subregion has spread out within this region, which also poses a great concern to the control and elimination of malaria in Yunnan Province. Currently, rare reported the malaria transmission risk in the border areas of Yunnan Province, herein, the study collected the data of malaria epidemiological and prevention and control interventions in 20 border countries of Yunnan Province from 2012 to 2014. The data contained the individual case information, vectors and capability of medical facility. Descriptive analysis, expert consultation, calculated risk index were applied to analysis of the malaria epidemiological characteristics in the border areas of Yunnan Province, and establish malaria risk assessment index system, to quantitative evaluate the level of risk and stratification of risk regions. The aim of this study was to stratification the risk areas in the border of Yunnan Province based on the townships, and provide the evidence-based proof for risk surveillance and emergence response.The main results were listed as follows:1. The malaria epidemiological characteristics in the border area of Yunnan ProvinceFrom 2012 to 2014, totally 1558 malaria cases were reported in 20 border counties, and among which the imported cases was 1336, account for 85.75% of the whole cases. The imported cases were mainly returned from Myanmar (n= 1,277,95.87%). Plasmodium vivax was the predominant species (n= 1,241,79.65%). Malaria cases occurred 51.47% in male and the highest malaria cases were observed in the age group of 21 to 40. The cases were peak during April to June (n=782,50.19%) and two death contributed to malaria were reported. Regarding to the spatial distribution, the imported cases mainly occurred in the counties of Tengchong (n= 459), Ruili (n= 366),Yingjiang (n= 191) and Mangshi(n=78). Indigenous cases mainly distributed in the counties of Yingjiang (n= 73), Gengma (n= 30), Mangshi (n= 26) and Cangyuan (n= 24).2. Establish the risk assessment index system for malaria transmission in border areas of Yunnan ProvinceThe risk assessment index system of malaria transmission in the border area were consisted of two levels, including 2 indexes in first level, and 8 indexes in second level. The malaria vector (0.2766) had the highest weight in first level, and the mainly various with high weigh in second level including malaria vector species (0.0234), number of reported imported cases for the last three years (0.0232), number of reported indigenous cases for the last three years (0.0224) and malaria control and prevention staffs per thousand population (0.0142) weighs the least.3. Risk stratification of border areasThe totally 197 townships in the border areas of Yunnan Province was stratification into three risk level regions:2 townships (Nabang in Yingjiang, Banlao in Cangyuan) were defined as high risk level,; 12townships were defined as moderate level risk township (Mangka and Banhong in Canyuan, Dulongjiang in Gongshang, Pianma in Lushui, Diantan in Tengchong,Zhina in Yingjiang, Mengyue in Longchuan, Xishang in Mangshi, Huyu in Ruili, Mengding in Gengma,Yuesong in Ximeng,Qushui in Jiangcheng,); 183 townships were defined as low risk level, which were distributed in each counties.Conclusion1. Despite the remarkable decrease of local malaria in China, the imported malaria has become the greatest challenge for border areas in Yunnan Province. Therefore, surveillance system needs to be well planned and managed to ensure timely recognition and prompt response to each imported cases.2. Select the key indicators in the elimination stage to establish the two level index system of the risk assessment of malaria transmission in the border area of Yunnan Province and provide the data support for the following risk assessment.3 The risk stratification of border areas in Yunnan Province showed that the first and second high risk township were less than 5%, which suggest that most of the countries in border areas exhibit low risk, and the high and moderate townships were clustered in few counties.