OBJECTIVESTo develop techniques which can be used to detect genetic material of measles virus from clinical samples to make diagnosis and differentiate atypical measles from other exanthematous infections early in clinical course.

METHODSA nested reverse transcriptase-polymerase chain reaction (RT-PCR) was developed to amplify gene fragment with the size of 301 bps from N gene of measles virus in throat swabs and urine samples collected from infants and children who were suspected measles cases. Before the test was used for clinical samples, preliminary tests were performed to determine the sensitivity and specificity of the test. The sensitivity of the test was determined by plaque assay using measles virus strain Edmonton and the specificity of the test was determined by cross-reaction with rubella virus, respiratory syncytial virus, influenza A and B viruses, enterovirus, adenovirus, human cytomegalovirus (hCMV), EB virus, and herpes simplex virus I. Serum specific IgM antibody against measles virus was also tested by ELISA.

RESULTSMeasles virus with the titer of 0.53 pfu could be detected by using the nested RT-PCR developed in this study. No amplification was found with the nested RT-PCR when rubella virus, respiratory syncytial virus, influenza A and B virus, enterovirus, adenovirus, hCMV, EB virus, and herpes simplex virus I were used as templates. Out of 116 throat swabs collected from suspected measles cases, 70 (60.3%) were measles RNA positive. For urine samples, 48 out of 74 (64.9%) were positive. Both throat swab and urine samples were collected simultaneously from 73 patients. Among those, 71 (97.3%) showed consistent results. Serum specimens were collected from 110 suspected patients. Among those, 65 (59.1%) and 61 (55.5%) were measles virus specific IgM antibody positive detected with ELISA kits from two different sources, respectively. Out of 110 sera samples, 106 (96.4%) showed consistent results. The consistency of the gene amplification and specific IgM antibody detection was 80.8% as shown by 84 out of 104 patients from whom throat swab and sera were collected at the same time.

CONCLUSIONThe data indicate that the nested RT-PCR developed in this study is sensitive and specific for detection of gene fragment of measles virus from clinical samples. The test is superior to the commonly used specific IgM antibody detection because of identifying gene material in early clinical stage, and even single clinical sample can be tested.