Molecular epidemiology of polioviruses

A worldwide effort is underway to eradicate poliomyelitis by the year 2000. Surveillance for wild poliovirus circulation is crucial to this effort. The use of molecular epidemiologic methods has enhanced the precision and reliability of poliovirus surveillance. Because poliovirus genomes evolve rapidly (similar to 10(-2) nt substitutions/site/yr) during replication in humans, the potential resolving power of the molecular epidemiologic studies based upon nucleotide sequence comparisons is very high. Evolution among wild polioviruses occurs by both nucleotide substitution (primarily to synonymous codons) and recombination. Sequence comparisons of poliovirus isolates have revealed the existence of numerous genotypes endemic to different regions of the world. Sequence diversity within a genotype is reduced by epidemics (as one lineage predominates), as well as by intensive immunization (as lineages are eliminated). Molecular epidemiologic approaches have been widely used within the Poliomyelitis Eradication Initiative to: (1) determine the sources of imported viruses, (2) follow the pathways of virus transmission, (3) monitor the progress of control activities, (4) identify reservoirs sustaining virus transmission (5) develop molecular reagents for the rapid detection of wild polioviruses in clinical and environmental samples, and (6) provide critical evidence that poliovirus eradication has been achieved.