Detection of dengue-4 virus in pune, western india after an absence of 30 years--its association with two severe cases.

Background: Difference in severity of dengue outbreaks has been related to virus serotype, genotype and clades within genotypes. Till the 1980 s, India and Sri Lanka reported low number of dengue hemorrhagic fever (DHF) cases despite circulation of all four serotypes of dengue virus (DENV). Since the 1990 s the occurrence of DHF has increased.