Recurrence of Japanese encephalitis epidemic in Wuhan, China, 2009-2010

Abstract

Background: Japanese encephalitis (JE) was once epidemic in most areas of China, including Wuhan, a city located in the central part of China. The incidence of JE dramatically decreased due to nationwide immunization with the live attenuated JE virus (JEV) vaccine, and no JE cases were reported during 2005-2008 in Wuhan. In 2009 and 2010, 31 JE cases reoccurred in this area. In this study, we investigated the causes of JE recurrence.

Methods and findings: All JE cases were laboratory-confirmed by detecting the JEV-specific IgM antibody with an IgM-capture enzyme-linked immunosorbent assay (ELISA). All patients were children between 2 months and 9 years of age with a median age of 2 years. Of the 31 cases, 9 had received one or two doses of the JEV vaccine, 11 had not been immunized previously with the JEV vaccine, and 11 had an unclear immunization history. Through reverse transcription polymerase chain reaction (RT-PCR), sequencing, and phylogenetic analysis, two new strains of JEV were isolated from Culex tritaeniorhynchus and identified as genotype 1 JEV, rather than genotype 3, which circulated in this area previously.

Conclusions: Vaccine failure or missed vaccination may have caused JE recurrence. Local centers for disease control and prevention need to improve immunization coverage, and the efficacy of the JE vaccine needs to be reevaluated in a population at risk for disease.

Figure 1. Incidence rate of Japanese encephalitis (JE) in Wuhan, China (1992–2004).

From 1992 to 2004, the incidence rate of JE decreased in Wuhan, China.

Figure 2. Phylogenetic tree based on the full E gene of the representative JEV strains.

The tree was constructed using the neighbor-joining method in Mega software version 4.0. The scale at the bottom of the tree indicates the number of nucleotide substitutions per site. Horizontal branch lengths are proportional to the genetic distance, while vertical branch lengths have no significance. The numbers above each branch represent the percentage of 1000 bootstrap replicate support. The tree was rooted using an outgroup sequence of Murray Valley encephalitis virus (MVEV). Newly isolated JEV strains in Wuhan are labeled with black diamonds on the left and belong to genotype 1. The older strain belonging to genotype 3 is labeled with a black square.