Nationwide Molecular Epidemiology of Measles Virus in Japan Between 2008 and 2017

Descriptive Analysis of Measles Outbreak in Liberia, 2022

Background

Liberia reported a large outbreak of measles involving all the counties in 2022. We conducted a descriptive analysis of the measles surveillance data to understand the trend of the outbreak and guide further policy action to prevent future outbreaks.

Methods

We analyzed the measles surveillance data from Epi week 1 to 51, 2022. All the laboratory-confirmed cases, clinically compatible and epidemiologically linked cases were included in the analysis, the variables of interest included the patient's age, sex, place of residence, measles classification, measles vaccination status, and outcome. We cleaned and analyzed the data using R version 4.2.0 and Arc GIS Pro. The demographic characteristics of the cases were presented, the progression of the cases was presented in Epicurve and the spatial distribution and the case fatality rate (CFR) of the case were presented at the district level using the Arc GIS Pro.

Results

The median age of the cases was 4 years (interquartile range: 2-8 years). Children under five years of age constituted 60% of the cases (4836/8127), and females accounted for 52% (4204/8127) of the cases. Only 1% (84/8127) of the cases had documentary evidence of receiving at least one dose of measles-containing vaccine (MCV). Only 3 out of 92 health districts in the country did not report a case of measles during the period under review. The overall cases fatality rate was 1% however CFR of up to 10% were reported in some districts.

Conclusion

The outbreak of measles involved almost all the districts of the country, exposing a possible nationwide suboptimal immunization coverage for MCV. The high CFR reported in some districts needs further investigation.

Achieving measles elimination and emerging modified measles: Longitudinal measles epidemiology from 1982 to 2021 in Osaka Prefecture, Japan

BACKGROUND

Measles is a contagious viral disease causing infant mortality in developing countries without vaccination programs. In Japan, measles vaccination was launched in 1978, surveillance commenced in 1981, and elimination was achieved in 2015. This was due to improved, legally required surveillance methods and vaccine programs.

METHODS

The data sets of sentinel (1982-2007) and notifiable (2008-2021) disease surveillance, as well as the vaccination coverage, detected genotypes, and seroepidemiology during the study period in Osaka Prefecture, were analyzed. Additionally, the trend under the current notifiable surveillance was compared before (2008-2014) and after (2015-2021) measles elimination.

RESULTS

Under sentinel surveillance, 51,107 cases were reported, predominantly infants aged 1-4 years (63.6 %). Under notifiable disease surveillance, the 781 patients were predominantly in their 20s-30s (43.7 %). From 2000, the age of the major susceptible group increased due to the rise in vaccination coverage, which exceeded 95% for the first dose in 1998 and 90% for the second dose in 2009. Consistent with these data, seroprevalence exceeded 95% in 2011. However, the geometric mean of the antibody titer showed a decreasing trend with a falling number of patients. Compared with before and after measles elimination, the number of modified measles cases increased from 10.1% to 48.2%. During the study period, 398 strains comprising eight genotypes were identified, and the dominant type changed over time. After measles elimination, genotypes B3 and D8, derived from imported cases, became predominant.

CONCLUSIONS

Improved vaccination coverage and surveillance reduced measles cases and increased herd immunity. However, the lack of a booster effect due to the low incidence of measles caused waning antibody titers despite high seroprevalence, which may contribute to the rising rate of vaccine failures causing modified measles. Careful monitoring of measles incidence and herd immunity are necessary for measles eradication.

Genetic Characteristics of Measles Viruses Isolated in Taiwan between 2015 and 2020

A genetic analysis of circulating measles virus (MeV) provides strong evidence of an interruption in endemic measles and supports the elimination status of this disease. This study investigated 219 MeVs isolated between 2015 and 2020. Based on the 450 nucleotide sequences of the nucleoprotein gene (N-450), three genotypes of the H1, D8 and B3 with 8, 18 and 6 different N-450 sequences, respectively, were identified. The H1 genotype virus has not circulated in Taiwan since 2017, and the D8 and B3 genotype MeVs became dominant between 2018 and 2019. Different D8 genotype variants were imported from neighboring countries, and the majority of MeV variants were detected only for a short period. However, MVs/Gir Somnath.IND/42.16[D8], a named strain designated by the World Health Organization (WHO), was detected over 2 years. To explore whether the endemic transmission of measles has been underestimated, another sequence window of the hypervariable, noncoding regions between the matrix (M) and fusion (F) genes (MF-NCR) was introduced to clarify the transmission chain. From the chronological sequence analysis of MeVs with N-450 and MF-NCR sequence windows, no endemic MeV variants lasted over 4 weeks, providing strong evidence to support the contention that Taiwan has reached the status for measles elimination.

Measles Outbreak Response Activity in Japan, and a Discussion for a Possible Strategy of Outbreak Response Using Cycle Threshold Values of Real-Time Reverse Transcription PCR for Measles Virus in Measles Elimination Settings

Measles is a highly contagious, but vaccine-preventable disease caused by the measles virus (MeV). Although the administration of two doses of measles vaccines is the most effective strategy to prevent and eliminate measles, MeV continues to spread worldwide, even in 2022. In measles-eliminated countries, preparedness and response to measles outbreaks originating from imported cases are required to maintain elimination status. Under these circumstances, real-time reverse transcription (RT) PCR for MeV could provide a diagnostic method capable of strengthening the subnational capacity for outbreak responses. Real-time RT-PCR can detect MeV RNA from patients with measles at the initial symptomatic stage, which can enable rapid public health responses aimed at detecting their contacts and common sources of infection. Furthermore, low cycle threshold (Ct) values (i.e., high viral load) of throat swabs indicate high infectiousness in patients with measles. The high basic reproduction number of measles suggests that patients with high infectiousness can easily become super-spreaders. This opinion proposes a possible strategy of rapid and intensive responses to counter measles outbreaks caused by super-spreader candidates showing low Ct values in throat swabs. Our strategy would make it possible to effectively prevent further measles transmission, thereby leading to the early termination of measles outbreaks.

A seroepidemiologic study of a measles outbreak, Yamagata Prefecture, Japan, 2017: The estimation of spreaders using serological assays in a measles elimination setting

INTRODUCTION

In regions where the endemic measles virus has been eliminated, early detection of contagious patients is important for preventing the spread of measles and sustaining elimination. To investigate whether serological assays can be used for the estimation of highly infectious patients with measles, we performed a seroepidemiologic study of a measles outbreak in Yamagata Prefecture, Japan, in 2017.

METHODS

We tested plaque reduction neutralization (PRN), IgG avidity, and gelatin particle agglutination (PA) assays in 31 patients with measles, subdivided into two super-spreaders, three spreaders, and 26 non-spreaders. Simultaneously, these results were compared with the cycle threshold (Ct) of a semi-quantitative real-time reverse transcription PCR for the measles virus from throat swab specimens.

RESULTS

In the PRN assay, one super-spreader and two spreaders lacked protective antibodies. The IgG avidity assay showed that two super-spreaders and one spreader had low avidity. The PA assay indicated that two super-spreaders and two spreaders lacked protective antibodies. Comparison of the results of the three serological assays and Ct revealed that patients whose antibody titers were judged as low in the IgG avidity and PA assays showed low Ct (i.e., high viral load), whereas non-spreaders tended to show low viral load.

CONCLUSIONS

Our preliminary seroepidemiologic analysis of a population of 31 patients with measles suggests that PA and IgG avidity assays may be used for the identification of super-spreader/spreader candidates. However, further investigations are necessary to validate the robustness of these serological assays in detecting contagious measles cases.

Optimisation of methodology for whole genome sequencing of Measles Virus directly from patient specimens

In an era of decreasing genetic diversity of Measles Virus (MeV), effective surveillance requires a higher-resolution genotyping method or whole genome sequencing (WGS) to document elimination. Through optimization of MeV WGS protocol, we developed a MeV-specific probe enrichment method that allows next generation sequencing from clinical specimens. With the probe enrichment method, 70% of specimens can be sequenced at a read depth of greater than 10 reads with minimal off-target sequences.

Genetic Characterizations and Molecular Evolution of the Measles Virus Genotype B3's Hemagglutinin (H) Gene in the Elimination Era

Measles virus (MeV) genotype B3 is one globally significant circulating genotype. Here, we present a systematic description of long-term evolutionary characterizations of the MeV genotype B3's hemagglutinin (H) gene in the elimination era. Our results show that the B3 H gene can be divided into two main sub-genotypes, and the highest intra-genotypic diversity was observed in 2004. MeV genotype B3's H gene diverged in 1976; its overall nucleotide substitution rate is estimated to be 5.697 × 10^-4 substitutions/site/year, and is slowing down. The amino acid substitution rate of genotype B3's H gene is also decreasing, and the mean effective population size has been in a downward trend since 2000. Selection pressure analysis only recognized a few sites under positive selection, and the number of positive selection sites is getting smaller. All of these observations may reveal that genotype B3's H gene is not under strong selection pressure, and is becoming increasingly conservative. MeV H-gene or whole-genome sequencing should be routine, so as to better elucidate the molecular epidemiology of MeV in the future.

Epidemiological and molecular characteristics of a measles outbreak in northern Vietnam, 2013-2014

BACKGROUND

A nationwide measles outbreak occurred in Vietnam between 2013 and 2014.

OBJECTIVES

To provide an overview on the 2013-2014 measles outbreak in northern Vietnam using epidemiological and molecular analysis of the measles virus (MeV).

STUDY DESIGN

Epidemiological information was collected from all suspected cases of measles/rubella. Serum and/or throat swabs were collected for laboratory confirmation of measles. MeV genomes were detected and sequenced for phylogenetic analysis.

RESULTS

A total of 9577 confirmed measles cases were reported in northern Vietnam with an incidence rate of 116.4/1,000,000 population. Of these, approximately 76.3% had unvaccinated or unknown vaccination history and 55.7% were under five years old. The outbreak started in a minority population from the mountainous area bordering Lao PDR and China and exploded in high-density population areas. Molecular analysis of MeV revealed co-circulation of genotypes H1 and D8, with H1 as the predominant strain, and divided into two clusters: cluster 1, sharing high similarity with those detected in China and Lao PDR, and cluster 2, circulating locally with unidentified origin. The minor D8 strains belonged to the D8-Frankfurt cluster.

CONCLUSION

The outbreak originated in and spread from a population with limited access to vaccines. Molecular analysis revealed co-circulation of MeVs with three different origins during the outbreak. This is the first report to provide an overview of the 2013-2014 measles outbreak in northern Vietnam, demonstrating the need for vaccination strategies against measles that are tailored to local conditions with enhanced molecular surveillance to achieve measles elimination.

Epidemiological Investigation and Virus Tracing of a Measles Outbreak in Zhoushan Islands, China, 2019

Background: Measles transmissions due to case importations challenge public health systems globally and herd immunities in all countries. In 2019, an imported measles case and its subsequently outbreak was found in the Zhoushan Islands. Here, the process of epidemiological investigation and virus tracing were summarized to provide references for the prevention and control of measles in the future. Materials and methods: The data on the demographic, epidemiological, and clinical manifestation of measles cases in this outbreak were collected. The 450 bp fragments of the measles virus (MeV) N gene were amplified and sequenced. The genome of the first imported case was further isolated. Then, the maximum-likelihood and time-scaled phylogenetic analysis was conducted. Results: A total of 28 measles cases were confirmed. Their onsets were between March 13 and May 18, 2019. The first patient was from the Ukraine. He was confirmed at the Fever Clinic in Zhoushan hospital on March 15, 2019 and at the same time, another patient had visited the hospital due to another illness and 10 days later, this second case had onset (March 25, 2019). The epidemic curve shows sustained community transmission. The majority of the following cases (19/26) were clustered on the Donggang street which was close to where the second case worked. The 22 measles virus strains successfully isolated from this outbreak all belonged to the D8.2a sub-cluster and clustered with the KY120864/MVs/GirSomnath.IND/42.16/[D8] which was the predominant genotype in the Ukraine during 2018-2019. The analysis of the complete D8 genotype genome pointed to the fact that this prevailing strain originated from India in 2015 and its substitution rate was estimated as 6.91 × 10^-4 (5.64-7.98 × 10^-4) nucleotide substitutions/site/year. Conclusion: This outbreak was caused by an imported case from the Ukraine. There was a possible nosocomial infection between the first case and the second case. Then, the second case played an important role in the spread of virus due to her occupation. The molecular phylogenetic analysis could help to track the origin of the virus. Increasing and maintaining the high level of vaccination coverage (≥95%) and an efficient response to imported cases are essential to prevent and control the recurrence and outbreak of measles virus.

Structural characteristics of measles virus entry

Measles virus, a member of the genus Morbillivirus, is highly contagious and still shows considerable mortality with over 100000 deaths annually, although efficient attenuated vaccines exist. Recent studies of measles virus haemagglutinin (MeV-H) and its receptor, including crystallographic and electron microscopic structural analyses combined with functional assays, have revealed how the MeV-H protein recognizes its cognate receptors, SLAM and Nectin-4, and how the glycan shield ensures effective vaccination. In addition, the crystal structure of the MeV-F protein indicated its similarity to those of other paramyxoviruses. Taking into account these data, several models of viral entry/membrane fusion of measles viruses and related paramyxoviruses have been proposed. Furthermore, anti-MeV-F inhibitors targeted to specific regions to inhibit MeV-F protein activation were reported, with potency for preventing MeV infection. The inhibitors targeted for entry events may potentially be applied to treatment of MeV-derived diseases, although escape mutations and drug profiles should be considered.