It is important to note that the National Malaria Control Programme in Myanmar was launched in 2016 and its goal is to eliminate malaria by 2030 [25, 26]. However, National Malaria Elimination Programme in China was initiated in 2010 and its final goal is by 2020 [1–3]. It is a 10-year difference and distinct stage in achieving the goal of elimination malaria between China and Myanmar. Despite national programme has included KSR II, but the support from national programme barely covered KSR II in Myanmar due to conflict with central government since 2012 . This situation resulted in an imbalance on border malaria control capacities between China and Myanmar, malaria including KSR II threatens the border areas of YNC.
In order to reduce malaria transmission and enhance the control capacities in KSR II, the pilot project on 3 + 1 strategy of joint cross-border malaria prevention and control was initiated in both sides and supported by both local funds. Due funding limitation and human recourses, + 1 area of Myanmar and 1st PL of YJC was set in a defined region, the width was limited to 2.5 Km from boundary that was based on the fact that An. Minimus is dominant malaria vector in this area [28–30], its maximum flight distance is 2.32 Km [31, 32], which purpose was to prevent mosquito transmission cross or along boundary by reducing vectorial capacity and building a flight buffer.
There was an outbreak in + 1 area of Myanmar in 2016 which API unusually increased 2.31 times higher than 2015 (OR 95%CI: 2.13–2.50, p value < 0.001) that matched the WHO description on malaria outbreak (Fig. 2 and Table 1) .Usually, malaria outbreaks in the Greater Mekong Sub-region are mostly ascribed to population movement and rarely to climatic factors . In spite of the difference of population between 2015 and 2016 was little (Table 1), the rate of bednet ownership and proportion (97.3% in 2013) of sleeping under bednet was high [27, 34], especially sleeping under LLINs/ITNs (76.1% in 2013) , malaria outbreak unexpectedly occurred during the implementation of local GF malaria program in 2016. Several reasons could explain included that most of male adult conscribed into the ethnic army and stationed in the forest where malaria high-transmission , they often returned home and carried malaria back communities or Usage of LLINs had expired . Why scaling up the proportion of LLINs distribution, coverage and use in the catchment areas of Myanmar during the tenth round China GF malaria program from 2011 to 2013, and those LLINs expired by 2015 . Also IDPs moving into local GF malaria program did not have enough LLINs to cover them again and rarely implemented indoor residual spraying (IRS) and treated bednets due to funding gaps to potential rebound of malaria transmission to pre-existing level .
Our findings showed that 96.27% of confirmed cases was P. vivax in the studied area, as WHO mentioned that it is more difficult to control or eliminate than P. falciparum due to its several distinct biological characteristics such as gametocytes in peripheral blood is matured to transmit to merozoites before symptoms appear; As malaria parasite density is often low to miss detection with microscopy or RDTs, hypnozoites in liver cell cause multiple relapse and need a 14-day course treatment of primaquine which patients may not fully adhere. Implemented pilot project had remarkable results in controlling malaria outbreak in + 1 area of Myanmar, effects of core WHO recommended malaria interventions and classical Chinese measures such as radical treatment at the resting stage [24, 35] (see Table 1).
In the first year (2017) of the pilot project, vector control in + 1 area of Myanmar was one net per bed to distribute new LLINs provided by Health Poverty Action (HPA) of nongovernmental organization. IRS and vector surveillance were not carried out due to preparation of materials and documents, other interventions were performed since April 2017. Our findings showed the API in + 1 area of Myanmar in 2017 had SSD than 2016 (p value = 0.026). This meant the results of malaria control in + 1 area of Myanmar in the first year was effective, but the API only reduced by 7% (95% CI: 1%-13%), malaria transmission was still high. In the middle of June in the second (2018) and third (2019) years, all houses in + 1area of Myanmar and 1st PL of YJC were simultaneously IRS used high-efficiency cypermethrin with WHO recommended dosage , and malaria vector was periodically monitored from the early of June to end of September, the other interventions were continue same as 2017. The results of malaria control in + 1 area of Myanmar had notably achievements in the past two years and both years’ API was sharply reduced by over 60% due the combinative effectiveness of IRS and LLINs. This is also trues as the proportion of An. minimus in the female anopheles was 63.7% high and had a positive correlation with number of malaria case (r = 0.74,p = 0.04), which unequivocally confirmed again it was predominant malaria vector in this area. Dong XS’s study had proven this mosquito rests indoor, prefers human blood and the biting peaks are in the sunset and midnight 
Consequently, IRS protects residents against this mosquito biting before they go to bed by killing mosquito that rest indoor, whereas LLINs protect residents after they go to bed by killing mosquito that rest on bednets, meanwhile, both interventions were high coverage and use in + 1 area of Myanmar. The combined effectiveness of both was maximally to reduce the human biting rate and vector survival, which significantly reduce vectorial capacity and transmission. Figure 3 showed the average monthly density of An. minimus sharply reduced in July after actualized IRS, the number of malaria case correspondingly sharply reduced in August. IRS and LLINs/ITNs are core interventions of vector malaria control recommended by WHO , both may be less effective in reducing P. vivax transmission. Conversely, our finding revealed that combined use of interventions in both settings have a significant positive effects and effectiveness in reducing An. Minimus vectorial capacity and competency.
Our findings revealed the average PCR PPR was1.58% in + 1 area of Myanmar, both result of the two surveys were low, but it was reliable and fitting the actual epidemic. This was because 3 RDTs positives were positive again detected with PCR and microscopy, if the 3 positives were as gold standards, the sensitivity and specificity of assay was both 100%, this result was same to findings by Zhou et al . CLIP-PCR is a high-throughput and highly sensitive PCR assay for detection Plasmodium spp. with a limits of detection of 0.01 parasites/µ l, which used dried blood spot and 96-well plate to directly detect parasite without purification of nucleic acid and tested at least 36 samples per well by pooling strategy [22, 23]. Additionally, 64 of 83 PCR positives were the submicroscopic infection, it accounted for 77% of all PCR positives, this result was similar to 67% of findings that overview of submicroscopic P. vivax infections by Moreira et al.  and Cheng et al. .Furthermore, Our finding indicated the average API in + 1 area of Myanmar was (59.11 ± 40.73) /1000 and ratio of P. falciparum/P. vivax was 0.04, consequently its transmission intensity was belonging to very low transmission according to the WHO category , especially, and the two surveys were conducted at the pre-epidemic and post-epidemic respectively. Due to limited sensitivity of microscopy and RDTs, measuring the accurate parasite prevalence in the low or very low transmission area are challenging . Findings showed the PPR of microscopy reduced by 100%, which proved the core interventions of case detection were very effective, local GF malaria program worked in a high ABER (Table 1).In spite of the submicroscopic PPR of the later survey was little higher than the previous, but there was no SSD between the two surveys, that related to low transmission and recently transmission reduction , this indirectly proved the effectiveness of the pilot project due to submicroscopic infection regarding as infectious parasite reservoir . These findings prompted contextual adoption of targeted interventions to control or eliminate this infection reservoir, such as to track the person who had same trip as case administer a same treatment, to administer a dose of chemprophylactics for case neighbors and families or to take radical treatment for P.vivax case at the resting stage. This finding also hinted that the source of infection still existed in + 1 area of Myanmar, once the vector control was weakened, malaria transmission would rebound again.
Interestingly, our findings showed that the number of cases reported by 1st PL accounted for 57% of the total cases in YJC and its AIR determined the trend of AIR in YJC. Meanwhile, Fig. 2 and Table 1 showed except that in 2018, the AIR in 1st PL reduced significantly with the decrease of API in + 1 area of Myanmar ( p value < 0.001), the others were little difference and did not change with API in + 1area of Myanmar. This finding revealed that most of the imported cases in 1st PL of YJC were from + 1 area of Myanmar, whereas 2nd PL and 3rd PL imported from Myanmar outside + 1 area. Because the explanation could be the annual cross-border population of YJC was relatively stable in recent years, and only small groups were population at risk (PAR) who stayed overnight or lived abroad. Usually, PAR were the certain residents of 1st PL and 2nd PL who long rent land of KSR II close to the border for cash crop cultivation, and a few of non-local and 3rd PL went to the interior of KSR II for planting and mining. However, among the border of 214.6 Km between YJC and KSR II, only LZC was the most serious malaria epidemic area and transmission was perennial with seasonal peak due to low altitude and dense population, the others were low epidemic areas and transmission was interrupted in the cold season due to high altitude. In particular, most of PAR in 1st PL lived in foothill and lowland plantations within + 1 area of Myanmar had high malaria transmission, which were relatively isolated and far away from Burmese villages .
Also the malaria consultation post in 1st PL of YJC which established by GF malaria program since 2007 was still working normally, most of PAR would take a dose of chemprophylactics before leaving the country and the new LLINs were freely available. That was why the AIR in 1st PL from 2015 to 2017 showed little difference and did not change with API of + 1area of Myanmar, but it sharply reduced in API after implementing all house IRS in 2018, then stable in 2019 due to a part of PAR lived outside + 1 area of Myanmar where no IRS. The research also found that all had SSD compared AIR in YJC and TPLs between 2019 and 2016 and proved the strategy of TPLs and its targeted local communities measures for each preventive line were effective.
Our study limitations include the average ABER was 40% of + 1 area and 66% of 1st PL, they were much higher than 2nd PL and 3rd PL due to the number of malaria tested in + 1 area including the number of tested in passive case detection and active case detection combined in report monthly. However, that number in TPLs was only passive case detection, not included active case detect. So, there was no comparability between + 1 area of Myanmar and TPLs of YJC. Furthermore, passive case detection in 1st PL detected all febrile patients, but 2nd PL and 3rd PL detected only 3 types of fever such as malaria fever, suspected malaria fever and fever of unknown cause. Bias due to the number of cases reported by 3rd PL was more than 2nd PL, this was because the rich people and non-local mobile population prefers to go to county-level hospitals where they could get better medical resources, as part of cases were transferred from 1st PL and 2nd PL to the county hospital for treatment.