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Intertypic genomic rearrangements of poliovirus strains in vaccinees
N Cammack1, A Phillips, G Dunn
1Division of Virology, National Institute for Biological Standards and Control, Herts, United Kingdom.
Abstract:
In vivo intertypic RNA recombination has previously been observed in excreted type 3 poliovirus isolates from a normal asymptomatic primary vaccinee. This study examines isolates from additional primary vaccinees to determine whether intertypic recombination is a general occurrence in excreted polioviruses. T1 RNase oligonucleotide finger-printing and limited dideoxy primer extension RNA sequencing demonstrated no evidence of intertypic recombination among type 1 or type 2 excreted strains. However, vaccinees excreting type 3 strains for long periods of time eventually produced recombinant strains involving either type 1 or type 2 poliovirus. Moreover, a characteristic time course of appearance of excreted type 3 intertypic recombinant polioviruses was established. Type 3/type 1 and type 3/type 2 recombinant strains appeared at Days 10-11 with a single crossover site in the gene for nonstructural protein 2C. Type 3/type 2/type 3 complex recombinant strains with an additional crossover site in the polymerase gene replaced type 3/type 2 strains at approximately Day 28. A significant portion of the genome of the type 3 Sabin vaccine strain is thus replaced during long-term excretion by vaccinees, and the appearance of some genomic arrangements coincided with a base deletion at the 3' terminus.
Insights
Intertypic RNA recombination is common in excreted type 3 polioviruses (poliovirus) during long-term shedding. Recombinant strains emerge with specific genetic changes and crossover sites over time.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- In vivo intertypic RNA recombination has been observed in type 3 poliovirus isolates.
- The frequency and characteristics of this recombination in excreted polioviruses require further investigation.
Purpose of the Study:
- To determine if intertypic recombination is a general occurrence in excreted polioviruses.
- To characterize the genetic makeup and timeline of appearance of recombinant poliovirus strains.
Main Methods:
- Analysis of poliovirus isolates from primary vaccinees using T1 RNase oligonucleotide fingerprinting.
- Limited dideoxy primer extension RNA sequencing to identify recombination events and crossover sites.
Main Results:
- No intertypic recombination was detected in type 1 or type 2 excreted poliovirus strains.
- Vaccinees excreting type 3 poliovirus for extended periods developed recombinant strains involving type 1 or type 2.
- Specific recombinant strains (Type 3/Type 1, Type 3/Type 2) appeared by Days 10-11 with crossovers in the 2C gene, followed by complex recombinants by Day 28.
Conclusions:
- Long-term excretion of type 3 poliovirus by vaccinees leads to significant genomic replacement via intertypic recombination.
- The emergence of recombinant polioviruses follows a characteristic timeline with specific crossover points.
- Genomic rearrangements in recombinant strains can coincide with 3' terminal base deletions.