Genetic Analysis of Measles Viruses
Molecular epidemiology of measles viruses is an important component in outbreak investigations and for global surveillance of circulating wild–type measles strains. During outbreaks, measles vaccine is administered to help control the outbreak, and in these situations, vaccine reactions may be mistakenly classified as measles cases. A small proportion of measles vaccine recipients experience rash and fever 10–14 days following vaccination. The vaccine strain of measles virus can be distinguished from wild-type viruses by determination of the genotype from clinical samples or virus isolates. (See Specimens for Measles Virus Isolation or RT-PCR Detection.)
Wild-type measles viruses have been divided into distinct genetic groups, referred to as genotypes, based on the nucleotide sequences of their hemagglutinin (H) and nucleoprotein (N) genes, which are the most variable genes on the viral genome.
The 450 nucleotides encoding the carboxy-terminal 150 amino acids (8 KB, 1 page) of the nucleoprotein has up to 12% nucleotide variation between genotypes. The 450 nucleotides that encode the carboxy-terminal region of the nucleoprotein (N–450) are required for determination of the genotype. The measles genotyping protocol is available from CDC.
For each genotype, a reference strain is designated for use in genetic analysis (phylogenetic analysis), usually the earliest known virus isolation of that group. The means of referring to the genotypes has been standardized using alphabetical designations for the main groupings (clades). Within the main clades, numerals are added to identify the individual genotypes.
The following 19 genotypes have been detected since 1990:
A*, B2, B3, C1, C2, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, G2, G3, H1, H2
*Vaccine strains Moraten, Edmonston, Zagreb are all genotype A.
There were 2 putative wild-type cases of measles identified as genotype A in 2008.
During 2011, 8 genotypes were identified by global surveillance:
B2, B3, D4, D8, D9, D11, G3, H1
Reporting Measles Sequences
A global measles sequence database, MeaNS, has been established at the Health Protection Agency in London, UK, and contains sequence information from more than 10,000 measles samples. Full access to MeaNS is given only to members of the WHO Measles and Rubella Laboratory Network (LabNet).
For more information, see CDC contact information. Sequences submitted to MeaNS are automatically submitted to the WHO Global Measles Genotype Database at WHO Headquarters in Geneva (https://workspace.who.int/sites/genotype/ for registered users). Sequences can also be submitted to GenBank. Measles sequences in GenBank are imported into MeaNS on a bi-weekly basis.
Guidelines for Naming Measles Strains or Sequences
The strain names will provide information that is essential for interpretation of the molecular data. Since sequence data may be derived from viruses isolated in cell culture or from RNA extracted directly from clinical material, strains or sequences will be designated as either:
- MVi: measles virus isolated in cell culture was source of RNA for sequencing or
- MVs: measles virus sequence derived from RNA extracted from clinical specimen
Other information to be included in the strain/sequence name:
- City/province where case of measles was diagnosed, write full name or abbreviation (required)
- Country, use WHO 3-letter ISO designation (required)
- Date of rash onset if know, otherwise date of specimen collection by epidemic week (1-52) and year (required)
- Isolate number if more than 1 per week in the same location (optional)
- Genotype [optional initially, required after sequencing of at least 450 nucleotides of the N gene (text-only) is completed]
- Special designation for sequences derived from measles inclusion-body encephalitis (MIBE), subacute sclerosing panencephalitis (SSPE) cases or vaccine reactions (VAC) (optional)
The following examples illustrate the WHO-approved nomenclature:
- MVi/NewYork.USA/03.98/2 [D2]
- MVs/London.UNK/17.97 [G3] SSPE
Download Measles Virus Nomenclature Update: 2012, published online in WHO's Weekly Epidemiological Record (WER), 2 March 2012. 87(9):73-80.
In order to maintain reference stocks of viruses and provide facilities capable of conducting viral sequencing, two global Measles Strain Banks have been established. The Measles, Mumps, Rubella and Herpesvirus Laboratory Branch of the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, USA, and Health Protection Agency (HPA) in London, UK, were selected to serve this purpose.
Upon request, viral sequencing and analysis can be provided for measles virus characterization as well as storage of viral strains. Laboratorians are requested to consult with the CDC Measles Laboratory before reporting a new measles genotype. To report a possible new genotype of measles, contact firstname.lastname@example.org
Dr. Paul Rota
Centers for Disease Control and Prevention
MMR and Herpesvirus Laboratory Branch
Atlanta, Georgia, 30333
Dr. Kevin Brown
Virus Reference Department
Health Protection Agency
61 Colindale Avenue
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