The last decade has shown the greatest reductions in malaria incidence in the GMS with the reported number of malaria cases falling by 76% between 2010 and 2018, and malaria deaths falling by 95% over the same period [1]. In China, malaria control has achieved great progress in the past decades, be caused of effective control of the malaria epidemic and ensuring the health of the population along with the promotion of social and economic development [34]. More intensive work on surveillance and response in malaria endemic areas was seen after the NMEP was launched in 2010 [9, 35, 36]. With a strengthening surveillance and response system, particularly for identifying the local and imported malaria cases, the implementation of surveillance and response was standardized as a “1-3-7” surveillance approach, which means case reporting within one day, case investigation within three days and focus investigation and action within seven days [37]. In our study, the total number of reported malaria cases in China fell 94.07% from 2005 to 2018 (Fig. 2).The majority of the counties with indigenous malaria cases reported were located along the China-Myanmar border [38]. There have been no malaria indigenous malaria cases reported in China since 2017 [11] and China is approaching malaria elimination nationwide in 2020.
Myanmar is reported to account for the vast majority of malaria cases and deaths in the GMS [13]. The proportion of confirmed cases in Myanmar was much lower prior to 2012 (Fig. 3b), which may have been caused by limited access to early malaria diagnosis and appropriate treatment in the community. In recent years, Myanmar has made significant progress in reducing malaria morbidity and mortality, with the reduction of malaria cases by 72% from 2012 to 2018, with a similar trend found in another study [39]. These achievements reflected a substantial improvement in case diagnosis and treatment and vector control, particularly at the periphery and among populations at risk of malaria, and increasing financial support from the Global Fund and other donors as well [40, 41]. In response to the threaten by the emergence and spread of P. falciparum resistant to artemisinin, the world’s first line antimalarial [42] in Cambodia, Thailand, Vietnam, Laos and Myanmar [4, 43, 44], WHO set its sights on malaria elimination in the GMS in order to contain this threat [6]. The National Plan for Malaria Elimination in Myanmar 2016–2030 has been developed with the goal of decreasing the API to < 1 in all states/regions by 2020, interrupting transmission of falciparum malaria in all states/regions by 2025 and eliminating malaria nationwide by 2030 [45, 46].
Although great gains have been made in reducing the overall cases of malaria, achieving an impact from elimination and control efforts proves more difficult in areas near international borders [47, 48]. The specific environmental (including physical, social and geopolitical), anthropological, administrative and geographic characteristics of border areas have a unique impact on the epidemiology of malaria. Cross-border malaria is difficult to manage because of political, economic and geographic constraints [49]. Border malaria is a major obstacle to achieving malaria elimination in the GMS [50]. China and Myanmar share a border of around 2000 km, which includes 18 counties in Yunnan Province of China and 13 townships from Kachin State, eight from Northern Shan State and two from Eastern Shan State in Myanmar [51]. The border counties on Yunnan side had the highest number of reported malaria cases in China [38] and the border townships in Myanmar had a relatively high transmission of malaria as well [52], resulting from lower access to health services, difficulties in deploying the prevention program to hard-to-reach communities, often in difficult terrain, and constant movement of people across porous national boundaries. The border counties in Yunnan Province are the key focus for malaria elimination in China and the 23 townships in Myanmar are one of the most difficult regions to be reached and covered by the NPME. This study showed that both reported malaria cases and API declined in the border counties or townships on both sides, but a few townships in Kachin State still had higher API, such as Injangyang, Momauk and Sumprabum. These townships should be the key focus for malaria elimination along this border.
When compared with P. falciparum, P. vivax is geographically the most widespread cause of human malaria with over 2.5 billion people living at risk of infection [53, 54]. Vivax malaria has a high prevalence in Southeast Asia, and in Central and South America. As reported by WHO, 53% of the P. vivax infection was in the WHO South-East Asia Region [1]. This study found that P. vivax was the predominant malaria parasite along the China-Myanmar border and the proportion of P. vivax infection increased from 61.64% in 2014 to 81.17% in 2018. In addition, P. vivax was more common on Chinese side than on the Myanmar side. The epidemiology of vivax malaria in this region is highly complex and P.vivax has become a major challenge for malaria elimination in the GMS [13, 55].
The number of reported malaria cases and the proportion of vivax infection in the 18 Chinese counties was strongly correlated with those in the 23 townships of Myanmar (P < 0.05). Interestingly, however, we did not find a correlation of API between the two sides. API is defined as the number of confirmed new cases expressed per 1,000 individuals under surveillance in a specific year, and it usually refers to areas of high and moderate malaria transmission risk [56, 57]. The study data was obtained from the China-Myanmar border, which showed low to moderate transmission of malaria with a large mobile population and local population. This may lead to the bias when API is used as an indicator for regression analysis.
Since 2014, a cross-border malaria prevention and control cooperation mechanism has been established between China and Myanmar to accelerate the control and elimination of malaria in this border region, and the strategic plan was drafted with "one zone one strategy" to promote the joint actions [7]. Efforts are underway to strengthen surveillance and to enhance reporting from the private sector and nongovernmental organizations (where relevant), with case-based surveillance and a response accelerating towards elimination. Based on the latest malaria epidemiology on the border, it is necessary to further promote the updating and implementation of this cooperation strategy and its action plan, highlighting the areas with high API in Myanmar side and high risk of malaria re-establishment in China side for achieving and maintaining the elimination in both the countries.
One limitation of this study is that reported malaria data was analyzed in a large scale, which was based on the county or township level. However, malaria cases were more scattered in the villages or communities in the pre-elimination or elimination stage. The further spatial-temporal analysis of malaria in small scale at village or community level will be more accurate.