Epidemiologic Analysis of Efforts to Achieve and Sustain Malaria Elimination along the China–Myanmar Border

Malaria cases have dramatically declined in China along the Myanmar border, attributed mainly to adoption of the 1-3-7 surveillance and response approach. No indigenous cases have been reported in China since 2017. Counties in the middle and southern part of the border area have a higher risk for malaria importation and reestablishment after elimination.

I n 2010, China issued the National Malaria Elimination Action Plan (2010-2020), with the goal of eliminating malaria nationwide by 2020 (1). Malaria cases in China subsequently decreased dramatically, and no indigenous cases have been reported since 2017 (2). In 2020, on the basis of successful subnational verifi cation, China submitted an offi cial request to the World Health Organization for certifi cation of national malaria elimination, which requires a country to provide evidence that local malaria transmission has been fully interrupted, that zero indigenous human malaria cases have been reported for >3 consecutive years, and that an adequate program for preventing reestablishment of indigenous transmission is fully functional throughout the country (3). However, the China-Myanmar border of Yunnan Province has attracted considerable attention because of a substantial risk of reintroduction of malaria from bordering areas of Myanmar (4). This border region is extremely remote, has high rates of poverty, and is inhabited by local minority nationalities (5,6). A total of 18 counties in Yunnan Province share the 1,997-km border with the townships of Myanmar in which malaria is endemic; the border provides no natural barriers and poses a high risk for malaria reintroduction into China.

The Study
We extracted data on reported malaria cases and foci during 2013-2019 from the web-based China Information System for Disease Control and Prevention and comprised data from passive case detection, reactive case detection among foci residents and case cotravelers, and proactive case detection among at-risk populations. Indigenous cases were defi ned as cases in patients who contracted malaria by bites from Anopheles mosquitoes within China without direct link to transmission from an imported case, whereas imported cases were defi ned as cases in patients who had exposure history in any malaria-endemic areas abroad before the onset of illness (7,8). Plasmodium spp. were determined by microscopy or rapid diagnosis test and PCR (8). This study was an epidemiologic analysis of malaria along the China-Myanmar border to identify the risk for malaria reestablishment in the stage after elimination.
During 2013-2019, a total of 2,222 malaria cases were reported from the 18 border counties; 1 death occurred. Total cases fell from 465 in 2013 to 148 in 2019; indigenous cases dropped to zero by 2017, and the number of imported cases also declined ( Table 1). This decrease was mainly attributed to the extensive adoption of the 1-3-7 approach to surveillance and response: case reporting within 1 day, investigation within 3 days, and focus investigation and response within 7 days. Case-patients ranged in age from 19 to 59 years, and men and outdoor workers were at considerably higher risk of contracting malaria (p<0.0001) ( Table 1).
P. vivax was the predominant species. P. vivax cases accounted for 95.7% of total reported cases during 2017-2019, whereas the proportion of P. falciparum declined to 1.4% (Figure 2, panel A). Four cases of P. malariae and 10 cases of mixed infections were reported; no P. ovale cases were reported. A total of 43 relapsing cases (P. vivax cases that recurred 1 month later with neither evidence of an epidemiologic link to additional cases nor as a result of incomplete clearance of original asexual parasites) were reported during 2013-2019, which indicates the need for adherence to the full primaquine regimen and possible resistance to the drug for eliminating the hypnozoites.
The malaria transmission peak was from April to August; another slight peak occurred from December to the following January (Figure 2, panel B). This transmission coincided with the local natural environment and was strongly correlated with the abundance of Anopheles spp. mosquitoes. Of note, double peaks were identified in July and November 2019. The first peak was postponed, whereas the second peak shifted 1 month earlier. This change was primarily caused by migration in the local population. The temporal distribution pattern of P. vivax and P. falciparum was different ( Figure 2, panel B) because P. falciparum cases were few and most were imported, mainly because of population movement and migration.
The median interval between onset of illness and diagnosis of malaria varied widely (range 2-10 days; Table 2), because the capability for diagnosis in some healthcare facilities was relatively low; training is needed to strengthen case detection and diagnosis capabilities. In addition, this range reflects the knowledge, attitudes, and practice gaps regarding malaria treatment-seeking of residents. The median interval between diagnosis and treatment was 0 days, except for in Ximeng County, which had a median interval of 0.5 days (Table 2). These rates indicate the capacity of hospital response was strong. The 1-3-7 approach was adopted nationally in China in early 2012 (10). During 2013-2019, all malaria cases were reported within 1 day, 95.6% of cases were investigated within 3 days, and in 8 of 18 counties 100% of cases were investigated within 3 days in all years studied. Longchuan, Gengma, and Yingjiang Centers for Disease Control and Prevention took >3 days to complete investigation of cases from remote areas. Malaria focus in China is defined as the circumscribed village or community with a reported case (11). During 2013-2019, a total of 97.9% (381/389) of foci were investigated and responded to within 7 days in 10 counties (Table  2). Depending on the nature of the focus and its state of transmission, the corresponding response actions were selected; these actions consisted of indoor residual spraying, reactive case detection, case treatment, and health education (7). No secondary cases have been reported because of the prompt and targeted interventions in all the foci.

Conclusions
China has set a goal to eliminate malaria by 2020, and Myanmar has set a goal to eliminate malaria by 2030 (1,12). This study demonstrated that local malaria transmission has been interrupted in Yunnan Province at the China-Myanmar border, although the risk for malaria reintroduction still exists. The complex geographic conditions and large migrant population along the border, in addition to reservoirs of symptomatic and asymptomatic infection in neighboring Myanmar (13), are obstacles to consolidating achievements in malaria elimination (5,14). Another noteworthy factor is the coronavirus disease pandemic. Maintaining full engagement with malaria control is challenging given the simultaneous demands of the pandemic (15).
In summary, malaria elimination has been achieved in the counties in China along the border with Myanmar. However, continued strong surveillance,   The datasets used and analyzed during this study are available from the corresponding author on request.