Detection of dengue virus RNA in patients after primary or secondary dengue infection by using the TaqMan automated amplification system

In consecutive serum samples from 25 tourists with acute dengue fever, viru s-specific RNA was detected by using fully automated TaqMan reverse transcr iptase PCR For this amplification technique new primers and special fluoroc hrome-labeled probes had to be synthesized. During amplification the increa sing amount of viral DNA could simultaneously be measured in the tightly se aled tubes. Dengue virus RNA was found in almost all patients (17 of 18), i f the samples had been taken soon after the onset of symptoms and before an ti-dengue virus antibody had been produced. RNA was detectable in only one of five persons who had anti-dengue virus immunoglobulin M (IgM) antibodies but not yet IgG antibodies. In 30 late samples with both IgG and IgM antib odies viral RNA was no longer demonstrable. In two early samples from two f requent travelers obtained 1 and 2 days after the onset of symptoms signifi cant Ige antibody titers were present but there were no anti-dengue virus I gM antibodies. In these samples a viral load of >5 x 10(6) dengue virus RNA copies (dengue types 1 and 2) was detectable. These findings of a high vir al load in the presence of anti-dengue virus Ige antibody are suggestive of a secondary dengue virus infection. In the 20 tourists (17 plus 1 plus 2) in whom viral RNA was found, the dengue virus serotype could be related to the area where the infection had taken place. Most of our patients came fro m southeast Asia and most frequently had dengue virus type 1 infections (8 of 20).