Genetic characteristics of wild-type measles viruses

Although measles virus (MV) is considered to be serologically monotypic, measles infections due to the wild-type virus can be distinguished from vaccine-associated cases, and the wild-type viruses can be classified into several genotypes.  The development of RT-PCR and sequencing methods has provided the possibility of molecular characterization of MV directly from clinical specimens by sequencing PCR amplicons.

By applying these molecular epidemiological methods significant contributions to measles control efforts have been made, by enabling investigators to identify the source and transmission pathways of the virus and to monitor circulating virus strains. This is particularly the case in countries where measles elimination efforts are underway.

The development of a sequence databases for wild-type measles viruses has made global molecular epidemiological studies of measles possible. Until 1998, there was no universally accepted scheme to describe the various genetic groups of measles virus.  Neither was there a uniform analysis protocol, so that data generated by one laboratory was not  comparable to data generated elsewhere. Two members of VRD staff contributed to the WHO meeting convened to agree methods for describing the major genetic groups of measles. This standardization will allow for more efficient communication between the various laboratories conducting molecular characterization of wild-type strains and will provide epidemiologists and public health officials from international, national and local agencies with a uniform nomenclature to describe cases, outbreaks and epidemics. 

The WHO has established two measles strain banks, one at the measles virus section of the Centers for Disease Control and Prevention (CDC) and the other at our Immunisation and Diagnosis Unit.  They will acquire, analyse, store and dispense representative strains.  Measles virus strains will be made available to all researchers without requirements for material transfer agreements.  The WHO strain banks will supply only wild-type viral isolates and samples of some vaccine strains.  In addition, sequence data for all reference strains and deposited wild-type strains will be available through the WHO strain banks or through GenBank.  Laboratories may submit viral isolates to the bank with or without sequence data.  In the latter case, the bank will perform sequence analysis.  Clinical specimens may also be submitted to the bank for testing.  If virus isolation is successful, representative strains will be sequenced and entered into the banks.

Last reviewed: 23 January 2008