A 150 nucleotide long region corresponding to adjoining segments of the genes encoding polypeptides VP1 and 2A of 84 poliovirus strains recently isolated from patients with paralytic poliomyelitis over the territory of the former Soviet Union (FSU) were characterized by sequencing and/or PCR amplification using specially designed primers. Eighteen isolates were found to be very closely related to one or another of the three Sabin vaccine strains. Three distinct classes of geographical genotypes (geotypes) were discerned among 42 wild-type (non-Sabin) strains of serotype 1. One such geotype (called A) was widely circulating in 1990–91 in the Caucasian (Azerbaijan and Georgia) as well as Asian (Kyrgyzstan and Turkmenistan) Republics; this geotype exhibited only weak relatedness to known strains isolated outside the FSU. On the other hand, a subset of strains belonging to another geotype (T) of serotype 1, which circulated in 1991 in Tajikistan, demonstrated very close relatedness to contemporaneous strains isolated in Pakistan, India and Jordan. Strains that were somewhat different, but belonging to the same T-geotype, were found also in Moldova and Georgia. Strikingly, the primary structure of the VP1/2A junction of certain T-geotype isolates differed from the corresponding region of Sabin 1 only in 13–15% of positions, thereby not reaching the upper limit accepted for a geotype. This observation raises, though does not prove, the possibility that at least the relevant segment of the T-geotype RNA originated from the vaccine strain. The third geotype of serotype 1 was represented by a single, perhaps imported, isolate. Four distinct subsets of a common geotype (C) were discerned among 24 wild-type isolates belonging to serotype 3. These strains exhibited a broad geographical distribution being found, in particular, in Armenia, Azerbaijan, Georgia, Turkmenistan and Tajikistan; on the other hand, the C-geotype strains exhibited only a relatively distant relatedness to a strain isolated outside of the FSU (in Oman).


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