Methods to test for low-density Plasmodium parasites infection
Objective To compare the results of three detection methods for Plasmodium falciparum and Plasmodium vivax.Methods The Plasmodium falciparum blood sample from Wuhan of imported malaria in March 2023 and Plasmodium vivax blood sample from Yichang of imorpted malaria in April 2023 were prepared to make two thick blood smears and counted.Serial dilutions(1∶4,1∶16,1∶64,1∶256,1∶1024,1∶4 096,1∶16 384,1∶65 536)were prepared using a blood sample drawn from a healthy person as diluent solution.Two blood smears for each concentration were made for microscopic examination and the rapid diagnostic test(RDTs)and real time fluorescence quantitative PCR were conducted at the same time.Results When the dilution concentration of the original blood sample of falciparum malaria sample was lower than 1∶16 384,that is,the density of protozoa was as low as 13/µL blood,the two microscopy results were negative.When the original blood sample of vivax malaria sample was diluted to a concentration of 1∶1 024,that is,the density of protozoa is as low as 55/μL blood,the microscopic examination result was one negative and one positive.When the falciparum malaria sample was diluted to a protozoal density of 13/µL blood,the RDTs test result was negative.The original blood samples of vivax malaria samples were tested negative using two different brands of RDTs reagents.The real-time fluorescence quantitative PCR test results of all dilutions of the two samples were positive.Among them,the protozoa density of the highest dilution concentration of the falciparum malaria sample was 3.2/μL blood,and the CT value was 32.788.The protozoa density at the highest dilution concentration of the vivax malaria sample was 0.86/μL blood,and the CT value was 35.057.Conclusions The real-time fluorescence quantitative PCR had better detection than the other two methods,but the cost was higher.The three methods could be used in different detection institutions to improve the accuracy and effectiveness in malaria detection.
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