Measles, a highly contagious respiratory disease, has been a global health priority for elimination. However, recent outbreaks in various countries, including China's neighbors, have posed challenges. This study focuses on the 2024 measles situation in Gansu Province, China, aiming to analyze the characteristics of the measles virus (MeV) genotype D8 and provide insights for elimination efforts.
The Challenge of Measles Elimination
Measles, once a common childhood disease, has seen a significant reduction globally due to widespread immunization since the 1960s. Despite this progress, no WHO region has sustained elimination, and countries like the Czech Republic, Albania, and Mongolia have experienced resurgences. China, with a historically low incidence in 2022, has seen a rise in cases since 2023, influenced by outbreaks in nearby countries.
Understanding MeV Genotypes
MeV has one serotype but is classified into 8 groups and 24 genotypes based on genetic differences in hemagglutinin and nucleoprotein. The distribution of genotypes varies by region and period. Since 2018, only B3, D4, D8, and H1 have been circulating globally. In China, H1a has been the dominant indigenous genotype for three decades, along with vaccine-associated genotype A and imported genotypes like B3, D4, D8, D9, D11, G3, and H2.
Gansu Province's Measles Landscape
Gansu Province's measles surveillance from 2005 to 2019 detected only the H1a genotype, while from 2020 to 2023, only genotype A was found. The D8 genotype was first detected in 2024. This study aims to analyze the molecular characteristics of the D8 genotype in Gansu, offering a scientific basis for measles control and elimination.
Methods and Findings
Nucleic acid-positive throat swab specimens from confirmed measles cases in Gansu's 14 municipal measles/rubella network laboratories in 2024 were collected. MeV RNA was extracted, and 634 nucleotides at the 3'-terminal of the nucleoprotein gene were amplified. A total of 120 sequences of a 450-nucleotide region within the nucleoprotein gene (N-450) were obtained, with 117 sequences of the D8 genotype and 3 of the A genotype. The D8 sequences formed two distinct clusters, with Cluster 1 showing mutations at a critical diagnostic primer-binding site, potentially affecting detection sensitivity.
Implications for Public Health
The findings suggest imported virus transmission. Sustaining vaccination programs with measles-containing vaccines in key areas and enhancing sensitive virus surveillance are crucial for measles elimination efforts. The cases detected in Gansu in 2024 are likely imported or linked to importation, highlighting the need for continued vaccination and highly sensitive monitoring.
Global Context and Future Steps
The D8 genotype has shown a global proliferation trend, with an increasing proportion of reports. In China, it has been a major imported genotype since 2009, associated with sporadic importation, non-endemic, and endemic transmission. The D8 sequences detected in Gansu in 2024 are similar to those found in China between 2012 and 2020, but they are distantly related in the phylogenetic tree, suggesting different transmission chains. Further monitoring and research are needed to understand the transmission dynamics and public health significance of the D8 genotype in Gansu.
Conclusion
This study provides a comprehensive analysis of the measles virus genotype D8 in Gansu Province, China, in 2024. The findings offer valuable insights for measles control and elimination efforts, highlighting the importance of sustained vaccination programs and sensitive virus surveillance. Further research and collaboration are essential to fully understand the global dynamics of measles and achieve the goal of elimination.
