Myanmar dengue outbreak associated with displacement of serotypes 2, 3, and 4 by dengue 1

Abstract

In 2001, Myanmar (Burma) had its largest outbreak of dengue-15,361 reported cases of dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), including 192 deaths. That year, 95% of dengue viruses isolated from patients were serotype 1 viruses belonging to two lineages that had diverged from an earlier, now extinct, lineage sometime before 1998. The ratio of DHF to DSS cases in 2001 was not significantly different from that in 2000, when 1,816 cases of DHF/DSS were reported and dengue 1 also was the most frequently isolated serotype. However, the 2001 ratio was significantly higher than that in 1998 (also an outbreak year) and in 1999, when all four serotypes were detected and serotypes 1, 2, and 3 were recovered in similar numbers. The large number of clinical cases in 2001 may have been due, in part, to a preponderance of infections with dengue 1 viruses.

Figure 1

Phylogenetic analysis of the nucleotide sequences of the E protein genes of dengue 1 viruses from Myanmar and of dengue 1 viruses from other localities. Bootstrap values of 100% are shown.

Figure 2

Relationship between weather conditions and the number of cases of dengue in Yangon, 1998–2001. (a) Comparison of the monthly admissions of dengue (dengue fever, dengue hemorrhagic fever, and dengue shock syndrome) patients to the Yangon Children’s Hospital with the total monthly rainfall. (b) The average monthly maximum and minimum temperatures in Yangon from 1997 to 2001 and the difference between these values.