Abstract
BackgroundTen uncommon natural type 3/type 2 intertypic poliovirus recombinants were isolated from stool specimens from nine acute flaccid paralysis case patients and one healthy vaccinee in China from 2001 to 2008.Principal FindingsComplete genomic sequences revealed their vaccine-related genomic features and showed that their first crossover sites were randomly distributed in the 3′ end of the VP1 coding region. The length of donor Sabin 2 sequences ranged from 55 to 136 nucleotides, which is the longest donor sequence reported in the literature for this type of poliovirus recombination. The recombination resulted in the introduction of Sabin 2 neutralizing antigenic site 3a (NAg3a) into a Sabin 3 genomic background in the VP1 coding region, which may have been altered by some of the type 3-specific antigenic properties, but had not acquired any type 2-specific characterizations. NAg3a of the Sabin 3 strain seems atypical; other wild-type poliovirus isolates that have circulated in recent years have sequences of NAg3a more like the Sabin 2 strain.Conclusions10 natural type 3/type 2 intertypic VP1 capsid-recombinant polioviruses, in which the first crossover sites were found to be in the VP1 coding region, were isolated and characterized. In spite of the complete replacement of NAg3a by type 2-specific amino acids, the serotypes of the recombinants were not altered, and they were totally neutralized by polyclonal type 3 antisera but not at all by type 2 antisera. It is possible that recent type 3 wild poliovirus isolates may be a recombinant having NAg3a sequences derived from another strain during between 1967 and 1980, and the type 3/type 2 recombination events in the 3′ end of the VP1 coding region may result in a higher fitness.
Highlights
Polioviruses, the causative agents of acute paralytic poliomyelitis, have three serotypes and are members of the human enterovirus C species of Enterovirus genus in the Picornaviridae family [1]
10 natural type 3/type 2 intertypic VP1 capsid-recombinant polioviruses, in which the first crossover sites were found to be in the VP1 coding region, were isolated and characterized
In spite of the complete replacement of neutralizing antigenic site 3a (NAg3a) by type 2-specific amino acids, the serotypes of the recombinants were not altered, and they were totally neutralized by polyclonal type 3 antisera but not at all by type 2 antisera
Summary
Polioviruses, the causative agents of acute paralytic poliomyelitis, have three serotypes and are members of the human enterovirus C species of Enterovirus genus in the Picornaviridae family [1]. Polioviruses are small, nonenveloped human enteroviruses in which the virion consists of 60 copies of each of four capsid proteins (VP4 to VP1) surrounding a 7,500 nucleotide (nt) positivesense, single-stranded polyadenylated RNA genome. A single polyprotein translated from the RNA strand is first cleaved into three polyprotein precursors: P1, P2, and P3. P1 is processed to yield four capsid proteins: VP4, VP2, VP3, and VP1. P2 and P3 are the precursors of nonstructural proteins: 2A to 2C and 3A to 3D [2]. Ten uncommon natural type 3/type 2 intertypic poliovirus recombinants were isolated from stool specimens from nine acute flaccid paralysis case patients and one healthy vaccinee in China from 2001 to 2008
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