Attempts were made to recover viruses from patients and mosquitoes during an epidemic of dengue hemorrhagic fever on an island in the Gulf of Thailand in 1967. LLC-MK2 cell cultures were used for isolation, and identification was done by plaque-reduction neutralization tests. Aedes mosquitoes were collected resting indoors and biting outdoors. Ten strains of dengue-4 were recovered from patients' serum. Nineteen strains of dengue-4 were recovered from pools of Aedes aegypti and 10 strains from pools of Aedes albopictus. The results suggest that both species were acting as vectors of dengue-4.
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