Sequence analysis of measles virus strains collected during
the pre- and early-vaccination era in Denmark reveals a considerable diversity
of ancient strains.
Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark. siig@biobase.dk
A total of 199 serum samples from patients with measles collected in Denmark,
Greenland and the Faroe Islands from 1964 to 1983 were analysed by PCR. Measles
virus (MV) RNA could be detected in 38 (19%) of the samples and a total of 18
strains were subjected to partial sequence analysis of the hemagglutinin gene.
The strains exhibited a considerable genomic diversity, which is at odds with
the assumption that one genome type prevailed among globally circulating MV
strains prior to the advent of live-attenuated vaccines. Our data indicate that
the similarity of the various vaccine strains is attributed to their having
originated from the same primary isolate. Consequently, it is implied that a
small number of clinical manifestations of MV worldwide from which strains
similar to the vaccine strain were identified were vaccine related rather than
being caused by members of a persistently circulating ancient genome type. The
Danish pre- and early-vaccination era MV strains seem to change the evolutionary
spectrum of genome types A, C2 and E into one coherent group, suggesting that
the genome types of MV strains circulating in the world at present do not
represent far ranging evolutionary lineages but merely members of an
evolutionary continuum of pre-vaccination era MV strains which by chance or due
to an improved capability survived the worldwide partial herd immunity
accomplished through vaccination.
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