MOLECULAR EPIDEMIOLOGY OF DENGUE-4 VIRUSES IN VIETNAM, 1997 – 2002

Vu Thi Que Huong

Pasteur Institute in Ho Chi Minh City

Dengue-4 (DEN-4) viruses, belonging to the family Flaviviridae, are one of four virus serotypes resulted in human Dengue fever/Dengue haemorrhagic fever (DF/DHF) and transmitted by Aedes aegypti mosquitoes. In Vietnam, after the absent period, DEN-4 viruses became predominant serotype of DHF outbreaks from 1999 to 2002. Thus, the molecular epidemiology of this serotype was studied.

One thousand nine hundred and eighty nucleotides from premembrane/ membrane/ envelope protein genes of 14 DEN-4 virus strains isolated from patients who had different manifestations (such as DF, DHF grade I, II, III and encephalitis) in Vietnam during 1997 – 2002 were sequenced and determined based on 4 pairs of designed primers and automatic sequencer.

Nucleic acid sequences of Vietnamese DEN-4 virus isolates were compared with each other and with 24 geographically and temporally distinct DEN-4 viruses in the world and 3 sylvatic DEN-4 virus strains. Phylogenetic analysis indicated that the DEN-4 viruses were separated into three genotypes. Genotype-I contains viruses from the Philippines (1956 – 1984), Thailand (1963) and Vietnam (1997). Genotype-II was divided into 2 subtypes. Subtype-IIA consists of viruses from Indonesia (1973) and Malaysia (2001). Subtype-IIB consists of viruses from Indonesia (1976 – 1977), Tahiti, Puerto Rico, Central and South America. Genotype-III consists of viruses from Vietnam (1998 – 2002), Sri Lanka and Thailand (1978 and 1984). Genotype-III seems to evaluate from genotype-I (Asian genotype). This is the new result in comparison with the other authors (Chungue, 1995; Lanciotti, 1997) and has also contributed to our understanding of the molecular epidemiology and worldwide distribution of DEN-4 viruses.