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During an outbreak of dengue hemorrhagic fever (DHF) in Jakarta, Indonesia in 1988, we attempted to isolate dengue virus using mosquito cells and a medium containing heparin. Whole blood, immediately after being drawn from patients, was inoculated into Aedes albopictus cell cultures temporarily maintained in the heparin-containing medium. The overall virus isolation rate was 25% (17 of 69) samples collected within three days after admission of the patients to hospital. No virus was obtained thereafter. The successful virus isolation was apparently not related to titers of anti-dengue virus hemagglutination-inhibiting antibodies present in patients' sera. The viruses were recovered from cases of each of the four World Health Organization grades of DHF without significant differences. The technique is simple and easily performed at bedside.

Dengue-1 (D1) Mochizuki strain was examined for its nucleotide and amino acid sequences of genomic RNA and the data obtained were compared with those of other selected virus strains reported previously. Genomic regions corresponding to C, preM and M proteins were the major subjects of study. Parts of E protein were additionally examined. Among the D1 viruses investigated, the Mochizuki virus which was isolated in 1943 in Japan was shown to be close to Philippine 836-1 strain isolated in 1984 and Nauru Island strain isolated in 1974 at the respective places, in contrast with Thai AHF 82-80 strain isolated in 1980 and Caribbean CV1636/77 strain isolated in 1977. At the same time, a difference was noted between the Mochizuki and Philippine/Nauru strains at the cleavage site of preM/M junction: Mochizuki possessed RRGKR/S sequence whereas the Philippine/Nauru had RRDKR/S. The glycosylation site in preM and hydrophobic regions at the carboxyl termini of M and E were well conserved. Significances of the data are discussed in connection with viral epidemiology and variation.

When athymic nude (nu/nu) and heterozygous littermate (nu/+) mice were injected intraperitoneally (i.p.) with a mouse-adapted strain of dengue virus (DV), the following differences were noted in the course of infection. (i) The average survival time of nu/nu mice was longer than that of nu/+ mice, although the mortality ratios were not significantly different. (ii) DV persisted in some of the nu/nu mice for long periods of time without exhibiting any symptoms but they died after prolonged incubation periods. These aspects were not observed in the nu/+ mice. (iii) Infected nu/nu mice produced IgM antibody only transiently in the early stage of infection but they did not subsequently show regular IgG antibody production which normally occurred in nu/+ mice. (iv) Piamatral and perivascular mononuclear cell infiltration in the infected brain was more intense in nu/+ than in nu/nu mice. It is suggested from these data that the course of DV infection in mice is affected by the availability of thymus-derived lymphocytes (T-cells). Infectious virus was detected in various organs and tissues of infected mice. The hearts of nu/nu mice tended to show higher virus titres than those of nu/+ mice, whereas the virus concentrations in the brain, skeletal muscle and lymph node were the same in both groups of mice. Specific DV antigen was revealed by the fluorescent antibody (FA) technique in cells located in the infected tissues.