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Case-based surveillance enhanced with measles virus detection/genotyping is essential to maintain measles elimination
Hiroko Minagawa1, Yoshihiro Yasui1, Hirokazu Adachi1
1Aichi Prefectural Institute of Public Health, Tsuji-cho 7-6, Kita-ku, Nagoya 462-8576, Japan.
Background:
Japan was verified as having achieved measles elimination by the Measles Regional Verification Commission in the Western Pacific Region in March 2015. Verification of measles elimination implies the absence of continuous endemic transmission. After the last epidemic in 2007 with an estimated 18,000 cases, Japan introduced nationwide case-based measles surveillance in January 2008. Laboratory diagnosis for all suspected measles cases is essentially required by law, and virus detection tests are mostly performed by municipal public health institutes. Despite relatively high vaccination coverage and vigorous response to every case by the local health center staff, outbreak of measles is repeatedly observed in Aichi Prefecture, Japan.
Methods:
Measles virus N and H gene detection by nested double RT-PCR was performed with all specimens collected from suspected cases and transferred to our institute. Genotyping and further molecular epidemiological analyses were performed with the direct nucleotide sequence data of appropriate PCR products.
Results:
Between 2010 and 2014, specimens from 389 patients suspected for measles were tested in our institute. Genotypes D9, D8, H1 and B3 were detected. Further molecular epidemiological analyses were helpful to establish links between patients, and sometimes useful to discriminate one outbreak from another. All virus-positive cases, including 49 cases involved in three outbreaks without any obvious epidemiological link with importation, were considered as import-related based on the nucleotide sequence information. Chain of transmission in the latest outbreak in 2014 terminated after the third generations, much earlier than the 2010-11 outbreak (6th generations).
Conclusion:
Since 2010, almost all measles cases reported in Aichi Prefecture are either import or import-related, based primarily on genotypes and nucleotide sequences of measles virus detected. In addition, genotyping and molecular epidemiological analyses are indispensable to prove the interruption of endemic transmission when the importations of measles are repeatedly observed.
Insights
Molecular analysis confirms that most measles cases in Aichi Prefecture, Japan, are import-related, not endemic. Genotyping and sequencing are crucial for verifying measles elimination despite repeated importations.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- Japan achieved measles elimination status in 2015, following nationwide case-based surveillance initiated in 2008.
- Despite high vaccination rates and robust public health responses, measles outbreaks continue to occur in Aichi Prefecture.
Purpose of the Study:
- To investigate the origin and transmission patterns of measles virus in Aichi Prefecture, Japan.
- To assess the role of molecular epidemiology in verifying measles elimination.
Main Methods:
- Detection of measles virus N and H genes using nested double reverse transcription-polymerase chain reaction (RT-PCR).
- Genotyping and molecular epidemiological analysis of virus nucleotide sequences.
Main Results:
- Between 2010-2014, 389 suspected measles cases were tested, with genotypes D9, D8, H1, and B3 detected.
- Molecular analyses linked cases and identified three outbreaks, all considered import-related.
- Transmission chains were shorter in later outbreaks, indicating successful containment.
Conclusions:
- Most measles cases in Aichi Prefecture since 2010 are import-related, confirmed by virus genotyping and sequencing.
- Molecular epidemiological tools are essential for confirming the interruption of endemic measles transmission amidst recurrent importations.
