three villages ( manduo , luoping , and tuofeng ; figure ) in tengchong county , located in the westernmost part of yunnan province , were selected for study because of their 20112013 malaria incidence , ecologic features related to malaria transmission ( i.e. , altitude and proportion of land used for rice cultivation ) , and housing and economic status . the villages range in altitude from 1,276 to 1,893 meters and have 1,115 households and a population of 4,904 ( detailed methods in technical appendix ) . location of 3 villages in tengchong county , yunnan province , china , in which study of transmission risk from imported plasmodium vivax malaria was conducted . during 20112013 , a total of 24 p. vivax malaria cases were reported from the study villages to the chinese information system for disease control and prevention ; all were classified as imported ( technical appendix ) , as determined by patients travel history ( 3 ) . all patients were adult men 1849 years of age , and most worked in business or mining . patients were radically cured with a regimen of chloroquine and primaquine , as recommended by national treatment guidelines . malaria vulnerability or importation risk ( i.e. , incidence of imported malaria cases per 1,000 population per year ) averaged 1.6 cases in the study area during 20112013 ( technical appendix table 1 ) . the average interval between symptom development and diagnosis of malaria was 2.4 days ; average interval between diagnosis and treatment was 1.5 days ( table 1 ) . all cases were reported within 1 day and investigated within 3 days ( table 1 ) . health workers performing active fever surveillance during the 2013 transmission season ( may  september ) visited each house at 2-week intervals , conducted a total of 7,680 household interviews and 38,960 interviews with village residents , and collected 399 blood samples from persons with history of fever during the previous 2 weeks . a total of 268 ( 67.2% ) samples were from local residents who reported no travel outside tengchong county within the past 2 weeks ; 131 were from mobile populations reporting travel . vivax isolates were detected by microscopy and pcr in 10 ( 7.6% ) persons in the mobile population ; no malaria infection was found in local persons ( technical appendix table 2 ) . to estimate human biting rates , mosquitoes were collected in each study village every 2 weeks by using volunteer outdoor human - landing catches during may a total of 5,576 mosquitoes were caught ; most ( 95% ) were anopheles sinensis mosquitoes . the average number of mosquitoes landing on a single person per night ( human landing rate ) was 2.7 ( table 2 ; technical appendix table 3 ) . sinensis mosquitoes tested for the villages of manduo , luoping , and tuofeng was 0.52 , 0.54 , and 0.61 , respectively ( technical appendix table 4 ) . the average human blood index ( i.e. , proportion of tested mosquitoes with ingested human blood ) was 3.8% in the surveillance areas ( table 2 ; technical appendix table 5 ) . average vectorial capacity ( i.e. , expected number of new human infections from 1 infected person within 1 day , assuming all mosquitoes with sporozoites are potentially infective ) of an . sinensis mosquitoes was 0.02 ( table 2 ) , indicating that 50 cumulative days would be needed for transmission of malaria from an infected person to another person , assuming that all female mosquitoes biting malaria - infected persons become infected and transmit . sinensis mosquitoes found to have ingested human blood ( i.e. , blood feeding rate ) was 15.6% ( 31/199 ) . the proportion of infected mosquitoes was 16.1% ( 5/31 ) , the rate of susceptibility of local an . * vectorial capacity , expected number of new human infections from 1 infected person within 1 day , assuming all mosquitoes with sporozoites are potentially infective . hbi , human blood index ( proportion of tested mosquitoes having ingested human blood . average number of mosquitoes landing on a single person per night ( ma ) . human blood index divided by days needed to complete gonotrophic cycle ( cycle of taking a blood meal and laying eggs ) .  probability ( p ) of a mosquito surviving 1 whole day . # time ( n ) needed for parasites to complete development from ingested gametocytes during blood meal to sporozoites in salivary glands , when parasites are transmissible to humans .  * * fraction of infected mosquitoes after duration of sporogony . duration of vector 's  life , in days , after surviving the extrinsic incubation period , calculated as the negative logarithmic reciprocal of the daily survival rate : 1/ln(p ) . an . sinensis mosquitoes were the main local vector for p. vivax and were widely distributed throughout this study area . the vector s susceptibility to imported p. vivax infection indicates potential for p. vivax malaria to be sustained in this region . although a recent field survey showed secondary transmission from patients with imported p. vivax malaria in other villages in tengchong county ( 2 ) , we identified no secondary infections in the study villages . sinensis mosquitoes are the most widely distributed malaria vector in china but have relatively low susceptibility to parasites compared with other malaria vectors ( 4 ) . sinensis mosquitoes were susceptible to imported p. vivax infection ; however , vectorial capacity of an . sinensis mosquitoes was lower than it was during the 1990s ( 0.05 ) in the same region ( 5 ) and much lower than reported in central china ( 0.3 ) in the 1980s ( 6 ) . the reduced vectorial capacity in the study region since the 1990s is likely attributable to the change in the dominant malaria vector species . historically , an . kunmingensis mosquitoes were the main malaria vector in tengchong county and accounted for 77% of total malaria vector density ; its vectorial capacity ( 0.3 ) was 10 times higher than that of an . kunmingensis mosquitoes ( < 5% of total malaria vectors ) were captured in our study , likely because of extensive residual insecticide use and improved housing , which reduce contact with this mosquito and vectorial capacity . high coverage ( > 90% ) of long - lasting insecticidal nets and indoor residual spraying has been achieved in southern china along the myanmar border since implementation of the national malaria elimination program in july 2010 . in early 2012 , a real - time surveillance system and response strategy (  1 - 3 - 7  ) was rolled out nationally ( 8) and substantially improved timeliness of malaria surveillance and response activities . during 20112013 , all malaria cases in the study area were reported within 1 day and investigated within 3 days , and screening of persons with fever was conducted within 7 days . other countries reporting few days ( range 3.08.2 days ) before testing and treatment of imported malaria reported similar results and no subsequent secondary infections ( 911 ) . in our study , additional testing by pcr for those reporting fever found no subpatent infections ( i.e. , slight infections with low parasitemia ) , a finding consistent with a recent review that showed no difference between pcr and microscopy for detecting parasites in symptomatic persons . however , a large proportion of p. vivax infections were subpatent in a cross - sectional survey of the general population in china ( 12 ) . rigorous evaluation of malaria elimination programs is essential for continuously improving the programs , targeting limited resources , and maintaining financial and political support . we used robust entomologic and epidemiologic metrics to assess malaria elimination in a border region . many national malaria control programs lack capacity to conduct entomologic surveillance to assess vectorial capacity . although our study shows evidence of successful malaria elimination , additional validated metrics to ascertain success are needed . recent efforts to compare the basic reproductive rate ( total number of malaria cases derived from 1 infective case and distributed by mosquitoes in the absence of immunity ) for imported versus local malaria cases provide a more nuanced and stable metric for measuring malaria elimination ( 13 ) . because this region has a unique ecology and distinct mosquito species composition , our findings need further validation to determine whether they can be extrapolated to other areas of china s border region ( 14 ) . technical appendix . detailed study methods and additional tables summarizing data on imported malaria cases , active fever surveillance , and entomologic investigations for study of transmission risk from imported plasmodium vivax malaria along the china
malaria importation and local vector susceptibility to imported plasmodium vivax infection are a continuing risk along the china  myanmar border . 
 malaria transmission has been prevented in 3 border villages in tengchong county , yunnan province , china , by use of active fever surveillance , integrated vector control measures , and intensified surveillance and response .