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 pr ecision and reliability of poliovirus surveillance. Because poliovirus genomes evolve rapidly (similar to 10(-2) nt substitutions/site/yr) d uring replication in humans, the potential resolving power of the mole cular epidemiologic studies based upon nucleotide sequence comparisons is very high. Evolution among wild polioviruses occurs by both nucleo tide substitution (primarily to synonymous codons) and recombination. Sequence comparisons of poliovirus isolates have revealed the existenc e of numerous genotypes endemic to different regions of the world. Seq uence diversity within a genotype is reduced by epidemics (as one line age predominates), as well as by intensive immunization (as lineages a re eliminated). Molecular epidemiologic approaches have been widely us ed within the Poliomyelitis Eradication Initiative to: (1) determine t he sources of imported viruses, (2) follow the pathways of virus trans mission, (3) monitor the progress of control activities, (4) identify reservoirs sustaining virus transmission (5) develop molecular reagent s for the rapid detection of wild polioviruses in clinical and environ mental samples, and (6) provide critical evidence that poliovirus erad ication has been achieved.