Studies on dengue virus infection in Thailand

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(1) Studies on hospitalized dengue patients and outpatients of fevers of unknown origin were carried out at Nakorn Phanom Provincial Hospital. Inoculation of patients'serum specimens into C6/36 cells isolated 31 dengue virus strains (19 type 2, 8 type 4, 4 type 1). Prevalence of type 4 dengue virus, next to type 2, was characteristic to the dengue epidemic in this study. The result genrally agreed with viral genome detection and typing by reverse transcriptase-polymerase chain reaction (RT-PCR), which was performed directly on serum specimens. RNA extraction prior to RT-PCR did not improve the efficiency to detect viral genome significantly. Cytokine levels (I 1-1beta, I 1-6, TNF-beta)in patient's sera did not correlate with clinical severity of the disease, with normal level of TNF-1. ELISA on anti-dengue IgG and IgM levels differentiated primary and secondary dengue cases. Sequential ELISA on blood or serum specimens dried on filter paper strips showed stability of anti-dengue IgG antibodies upto 4 months storage at room temperature, with instability of IgM-antibodies , particularly in sera from primary dengue cases.(2) Entomological studies were carried out in the Faculty of Tropical Medicine, Mahidol University. Oral infection to 3 Aedes aegypti strains did not reveal significant difference between the infection rates of dengue type 2 virus strains, which had been isolated from different clinical severity of the disease. Larvicidal effect on Aedes aegypti sgiwed that LC_<50> of an insect growth regulator, pryproxifen, was 0.01 ^- 0.05ppb. The female adults, exposed to the compound, carried it to the larval habitat, resulted in larvicidal effect.