Molecular epidemiology of measles viruses in China, 1995-2003

Abstract

This report describes the genetic characterization of 297 wild-type measles viruses that were isolated in 24 provinces of China between 1995 and 2003. Phylogenetic analysis of the N gene sequences showed that all of the isolates belonged to genotype H1 except 3 isolates, which were genotype A. The nucleotide sequence and predicted amino acid homologies of the 294-genotype H1 strains were 94.7%-100% and 93.3%-100%, respectively. The genotype H1 isolates were divided into 2 clusters, which differed by approximately 2.9% at the nucleotide level. Viruses from both clusters were distributed throughout China with no apparent geographic restriction and multiple co-circulating lineages were present in many provinces. Even though other measles genotypes have been detected in countries that border China, this report shows that genotype H1 is widely distributed throughout the country and that China has a single, endemic genotype. This important baseline data will help to monitor the progress of measles control in China.

Figure 1

The geographic distribution of Chinese measles isolates from 1995 to 2003. No isolates were received from provinces in white.

Figure 2

Average number of measles cases (blue bars) and reported death (black bars) and average measles incidence (red line) between 1991 and 2003 in China. Number of reported deaths for each year is indicated above each black bar.

Figure 3

Schematic phylogenetic tree of the N gene sequences of 191 wild-type measles isolates from China compared to the WHO reference sequences for each genotype. For simplicity, strain names are not shown. Sequences from viruses isolated in China from 1995–2003 are indicated by red branches and dots, and WHO reference strains and Shanghai-191 vaccine strain are indicated by blue branches and dots. Positions of the reference strains for genotypes H1 and H2 are indicated by arrows.

Figure 4

Phylogenetic tree of the N gene sequences of 188 wild-type measles isolates from China in genotype H1. The WHO reference strains and another strain on the intermediate cluster are shown in red. Cluster 1 is shown in black, while cluster 2 is shown in blue. WHO strain name is indicated for each sequence.

Figure 5

Phylogenetic tree of wild-type measles viruses isolated in Henan (panel A) and Shandong (panel B) provinces between 1995 and 2003. Recent viruses from Henan are shown in red and recent viruses from Shandong are shown in blue. The intermediate cluster containing the reference sequence for genotype H1 and older strains is shown in black. Reference strains for genotypes H2 and A are also shown.