Sequence analysis of hemagglutinin and nucleoprotein genes of measles viruses isolated in Korea during the 2000 epidemic

Molecular epidemiology of measles virus infection in Shanghai in 2000-2012: the first appearance of genotype D8

Purpose

The purpose of this study was to identify measles virus in Shanghai in 2012 and study the genotype trend of measles virus epidemic strains during 2000–2012.

Methods

Nose and throat swab specimens were collected from 34 suspected measles cases in Shanghai. Measles virus was isolated using Vero-SLAM cells (African green monkey kidney cells/lymphoid signal activating factor-transfected African green monkey kidney cells). The 450 bp of C terminus of the N gene and the entire hemagglutinin gene sequence was amplified using RT-PCR. Phylogenetic analysis was performed by comparing the seven measles strains in Shanghai with the reference strains for H1a, H1b and D8 genotypes, as well as the Chinese measles virus vaccine strain.

Results

Seven measles viruses strains were isolated from the 34 throat swap specimens. Six strains were genotype H1a, which is the predominant strain in China and one strain was genotype D8, which is the first imported strain since 2000. All these seven strains maintained most of the glycosylation sites except subtype H1a, which lost one glycosylation site.

Conclusion

Since 2000, measles virus strains in Shanghai are consistent with measles virus from other provinces in China with H1a being the predominant genotype. This study is also the first report of genotype D8 strain in Shanghai. All strains maintained their glycosylation sites except H1a that lost one glycosylation site. These strains could still be neutralized by the Chinese measles vaccine. We suggest that Shanghai Center for Disease Control laboratories should strengthen their approaches to monitor measles cases to prevent further spread of imported strains.

Molecular epidemiology of measles virus

Genetic characterization of wild-type measles viruses provides a means to study the transmission pathways of the virus and is an essential component of laboratory-based surveillance. Laboratory-based surveillance for measles and rubella, including genetic characterization of wild-type viruses, is performed throughout the world by the WHO Measles and Rubella Laboratory Network, which serves 166 countries in all WHO regions. In particular, the genetic data can help confirm the sources of virus or suggest a source for unknown-source cases as well as to establish links, or lack thereof, between various cases and outbreaks. Virologic surveillance has helped to document the interruption of transmission of endemic measles in some regions. Thus, molecular characterization of measles viruses has provided a valuable tool for measuring the effectiveness of measles control programs, and virologic surveillance needs to be expanded in all areas of the world and conducted during all phases of measles control.

Genetic characterization of measles viruses in China, 2004

Genetic characterization of wild-type measles virus was studied using nucleotide sequencing of the C-terminal region of the N protein gene and phylogenetic analysis on 59 isolates from 16 provinces of China in 2004. The results showed that all of the isolates belonged to genotype H1. 51 isolates were belonged to cluster 1 and 8 isolates were cluster 2 and Viruses from both clusters were distributed throughout China without distinct geographic pattern. The nucleotide sequence and predicted amino acid homologies of the 59 H1 strains were 96.5%-100% and 95.7%-100%, respectively. The report showed that the transmission pattern of genotype H1 viruses in China in 2004 was consistent with ongoing endemic transmission of multiple lineages of a single, endemic genotype. Multiple transmission pathways leaded to multiple lineages within endemic genotype.

Review of the temporal and geographical distribution of measles virus genotypes in the prevaccine and postvaccine eras

Molecular epidemiological investigation of measles outbreaks can document the interruption of endemic measles transmission and is useful for establishing and clarifying epidemiological links between cases in geographically distinct clusters. To determine the distribution of measles virus genotypes in the prevaccine and postvaccine eras, a literature search of biomedical databases, measles surveillance websites and other electronic sources was conducted for English language reports of measles outbreaks or genetic characterization of measles virus isolates. Genotype assignments based on classification systems other than the currently accepted WHO nomenclature were reassigned using the current criteria. This review gives a comprehensive overview of the distribution of MV genotypes in the prevaccine and postvaccine eras and describes the geographically diverse distribution of some measles virus genotypes and the localized distributions of other genotypes.

Genetic Analysis of Measles Viruses Isolated in the United States between 1989 and 2001: Absence of an Endemic Genotype since 1994

This report describes measles virus surveillance in the United States for 1989-2001. During the resurgence of measles in the United States between 1989 and 1992, only viruses of genotype D3 were isolated. In contrast, virological surveillance conducted after the resurgence period showed that at least 12 different genotypes were associated with the greatly reduced number of measles cases. Eight different genotypes were identified for 27 chains of transmission in which the source of infection was unknown. The diversity of measles virus genotypes observed in the United States between 1994 and 2001 reflected multiple imported sources of virus and indicated that no genotype of measles is endemic in the United States. Therefore, the data obtained from virological surveillance are consistent with the conclusions made by disease surveillance and epidemiological investigations that measles is no longer an endemic disease in the United States.

Molecular epidemiology of measles virus in Japan

BACKGROUND

Measles virus has been classified into 22 genotypes. The present report examines the molecular epidemiology of measles virus in Japan from 1984 to 2002, and the epidemiological link between imported cases in several foreign countries and Japanese strains was elucidated from the literature.

METHODS

B95a or Vero cells was used to isolate the measles virus. The measles virus genome was amplified in the N and H genes by reverse transcriptase-polymerase chain reaction and were partially sequenced. Phylogenetic analysis of a partial sequence of the N gene, from position 1230 to 1685, of the recent measles strains was performed in comparison with the World Health Organization reference strains.

RESULTS

There were large outbreaks of measles in Japan in 1984, 1987-1988, 1991-1993, and 2001-2002 and each outbreak was caused by a different genotype. Genotype C1 was an indigenous strain for a long period before 1985, while D3 was isolated in 1987-1988 and D5 in 1991-1993 outbreaks. In addition, the Chicago-type D3 caused sporadic regional outbreaks from 1998 to 1999. After 2000, H1 became the dominant circulating strain. It should be noted that the Japanese strains were detected as imported cases by epidemiological linkage in several countries.

CONCLUSIONS

Among the recent circulating strain of measles virus in Japan the genotype H1 was dominant after 2000 and the Japanese strains D3, D5, and H1 were exported to several countries. It is recommended that Japan should adopt a more extensive and active vaccination strategy for measles elimination in line with other countries in the world.

Genetic and antigenic characterization of measles viruses that circulated in Korea during the 2000-2001 epidemic

Despite the marked reduction in the incidence of measles in Korea by the introduction of measles vaccine, a large measles epidemic occurred during 2000-2001. During the epidemic, more than 55,000 measles cases were reported and at least 7 children were dead. In this study, we analyzed the genetic and antigenic properties of 15 measles viruses that isolated during the epidemic. Sequence analyses of entire hemagglutinin (H) and nucleoprotein (N) genes of the viruses indicated that all Korean isolates had a high degree of homology (>99.8%) when compared with each other. They differed from other wild-type viruses by as much as 6.8% in the H gene and 6.5% in the N gene at the nucleotide level. The deduced amino acid variability was up to 6.4% for the H protein and up to 6.5% for the N protein. Phylogenetic analysis of nucleotide sequences and deduced amino acid sequences of the H and N genes revealed that all Korean viruses were grouped into the genotype H1. This strongly demonstrated that single genotype of measles virus has been circulated in Korea during the 2000-2001 epidemic. Plaque reduction neutralizing antibody titers against vaccine strains, Edmonston and Schwarz, and recently isolated Korean strains were measured using sera from vaccinees and recently infected children. Although sera of recently infected children demonstrated higher neutralizing antibody titers against wild-type strains than against vaccine strains, both sera neutralized both strains and the reciprocal geometric mean titers (GMTs) were not significantly different against both strains.

H1 genotype of measles virus was detected in outbreaks in Japan after 2000

We investigated the molecular epidemiology and biological characteristics of wild measles viruses isolated since 1984 in Japan. The circulating measles virus was of genotype C1 before 1985, D3 from 1987 to 1990, and D5 from 1990 to 1997. It was replaced by the same cluster of Chicago-type D3 strain from 1997 to 1999. In 2000, D5 recirculated with sporadic cases caused by genotype H1. The H1 genotype became dominant in 2001 with a minor distribution of D5. No significant difference was observed in neutralizing titers against C1, D3, D5, and H1 when we used sera having high neutralizing titers. However, some D3 and H1 strains were not completely neutralized with low levels of neutralizing antibody, and maintaining high levels of measles antibodies would be required for the control measles outbreaks.

Update on the global distribution of genotypes of wild type measles viruses

Molecular characterization of measles viruses is an important component of measles surveillance because these studies enhance our ability to identify the source and transmission pathways of the virus. Molecular surveillance is most beneficial when it is possible to observe the change in virus genotypes over time in a particular region. Such information can help to document the interruption of transmission of measles virus and thus provide an important method for assessing the effectiveness of vaccination programs. It is recommended that virus surveillance be conducted during all phases of measles control and be expanded to give an accurate description of the global distribution of measles genotypes. This review provides updated information on the circulation patterns of measles genotypes and examples of the utility of virologic surveillance.

Current status of measles in Japan

Approximately 20,000 to 30,000 cases of measles are reported annually in Japan, although the actual number of measles infections is considered to be five to ten times higher than the number of reported cases. Despite the availability of effective and safe live attenuated vaccines, regional outbreaks in Okinawa, transmission in adults, and secondary vaccine failures continue. Recent advances in molecular technology have contributed to molecular epidemiological studies, new concepts of asymptomatic infection, and the identification of different characteristics among measles virus genotypes. Measles virus strains isolated in Japan since 1984 were classified into the genotypes C1 (-1985), D3 (1985-1990), D5 (1990-1997), and Chicago-type D3 (1997-1999) from the results of sequencing the hemagglutinin gene. After 2000, the D5 genotype emerged, and, recently, the H1 genotype, which is now dominant, was introduced from Korea. Some of the currently circulating wild-types have different characteristics (high growth rate at 39 degrees C-40 degrees C). The cumulative vaccine coverage has reached 81%, but most measles cases involved unvaccinated individuals. Measles is a preventable disease and can be eradicated by increasing the vaccine coverage, and promoting the motivation for vaccination, in accordance with the worldwide measles strategy.

Studies of measles viruses circulating in Australia between 1999 and 2001 reveals a new genotype

Nineteen distinct measles virus (MV) strains associated with nine different genotypes were identified in five Australian states (Victoria, New South Wales, Queensland, Northern Territory and Western Australia) between 1999 and 2001. One of the strains identified is likely to represent a new genotype within the clade D viruses (proposed to be d9). No evidence for an indigenous MV strain was found. When epidemiologic information associated with the index case was available for the outbreaks, it usually supported introduction of the virus from overseas, with the main source being South East Asia. Changes in the circulation of MV in Australia since the early 1970s were also observed. Prior to the introduction of measles vaccine, the majority of the population acquired immunity through infection with wild-type virus in early childhood. Nowadays in Australia, young adults are at most risk of infection. The age range of cases in the study period was from 1 month to 48 years, with the majority (59%) of cases from individuals aged 18-30 years.

Molecular epidemiology of measles viruses in the United States, 1997-2001

From 1997 to 2001, sequence data from 55 clinical specimens were obtained from confirmed measles cases in the United States, representing 21 outbreaks and 34 sporadic cases. Sequence analysis indicated the presence of 11 of the recognized genotypes. The most common genotypes detected were genotype D6, usually identified from imported cases from Europe, and genotype D5, associated with importations from Japan. A number of viruses belonging to genotype D4 were imported from India and Pakistan. Overall, viral genotypes were determined for 13 chains of transmission with an unknown source of virus, and seven different genotypes were identified. Therefore, the diversity of Measles virus genotypes observed in the United States from 1997 to 2001 reflected multiple imported sources of virus and indicated that no strain of measles is endemic in the United States.