Screening Radius Of Active Case Detection And The Malaria Parasite Rate Of Carriers In China-Myanmar Border

Objective:To explore the effective screening radius of active case detection of the 1-3-7 surveillance and response strategy, and investigate the malaria parasite rate of asymptomatic malaria carries in China-Myanmar border for providing scientific evidence of malaria elimination in China.Methods:1. Three villages with indigenous malaria cases in Yingjiang County of Yunnan Province and one refugee camp of Myanmar were selected as study sites, but active case detection only conducted at the three villages in Yingjiang County.2. Inhabitants lived around the indigenous cases (index case) with the radii of 100 m,300 m,500 m of 1km were screened, and a blood filter paper and a thick and thin blood smear were collected from their earlobe. GPS located data about every house of participants contained index cases were obtained to calculate the screening radius.3. Every sample was detected by microscopy, nested PCR and real-time PCR. Comparison of results about three methods indentified the most sensitive method to detect asymptomatic malaria carriers.4. Based on the results of real-time PCR, the number of asymptomatic carriers at different radii were analyzed to obtain the effective screening radius of active case detection and the parasite rate of study sites were calculated.Results:1. Among 388 blood samples,6 asymptomatic malaria carriers were detected by microscopy with the parasite rate of 1.55%,11 by nested PCR with 2.83%,13 by real-time PCR with 3.35%. According the results of real-time PCR, the parasite rate of Nabang town and refugee camp of Myanmar were higher than that of Zhina town with statistic difference (P<0.05). However the parasite rate was similar at Nabang town and the refugee camp of Myanmar with no statistic difference(P>0.05). Importantly, among all positive asymptomatic cases, there was only one Plasmodium falciparum (7.69%,1/13) and the remain was Plasmodium vivax(92.31%,12/13).2. As the gold standard of microscopy, the sensitivity and specificity were 100.00% and 98.69% for nested PCR,100.00% and 98.69% for real-time PCR. Meanwhile the parasite rate of asymptomatic carriers by nested PCR and real-time PCR were higher than that by microscopy with statistic difference(P<0.05), the parasite rate by nested PCR was similar to that by real-time PCR with no statistic difference(P>0.05).3. Based on the results of real-time PCR at three villages of active case detection (except for refugee camp of Myanmar),2,5 and 0 asymptomatic cases had found at 0-100m,101-300m and 301-1000m respectively; the proportion of asymptomatic carriers was 28.57% within a 100m screening radius and 100.00% within a 300 screening radius after analyzing results at different screening radii.Conclusion:1. The parasite rate of asymptomatic malaria carriers in China-Myanmar border area was about 3.35% by PCR technologies, and Plasmodium vivax was the main infections.2. Microscopy was not effective way to detect the asymptomatic malaria carriers, however PCR technologies have a good sensitivity and specificity to detect these infections.3. The asymptomatic malaria carriers can be effectively detected within a 300 m screening radius of index case by PCR technologies.