What are the repercussions of the oral polio vaccine on the world of enteroviruses?

To eradicate poliomyelitis and poliovirus, intensive vaccination campaigns with oral polio-vaccine (OPV) have been organised. Eradication campaigns ma y well be successful because the antiviral immunity and the local intestina l immunity due to OPV in particular avoids and/or limits poliovirus circula tion. These campaigns give interesting opportunities for studying the impac t of viral vaccines on the viral world in terms of ecological and genetic v irology. The pre-eradication phase we are now entering brings with it two k inds of problems, First, the major disadvantage of OPV is the genetic and phenotypic variabil ity of the vaccine strains. This variability leads to the spread of potenti ally pathogenic strains, which can be implicated in vaccine-associated para lytic poliomyelitis (VAPP). Genetic changes are characterised by point muta tions and by genetic exchanges among OPV strains, between OPV and wild stra ins and perhaps between poliovirus and non-polio enteroviruses (ENPV). The fact that a few OPV mutant strains have been shown to multiply and/or to ci rculate for long periods suggests that OPV could sustain a reservoir of pat hogenic poliovirus strains. Second, there are ecological considerations. The disappearance of wild poli ovirus through OPV vaccination could be due not only to antiviral local imm unity but also to competition between OPV strains and wild strains for infe cting the digest tract. Moreover a competition between OPV and other entero viruses may take place in a common ecological niche. To our knowledge the p ossible impact of intensive OPV vaccination campaigns on the ENPV populatio ns has never been considered. Because the goal of poliovirus eradication ma y be reached in the near future, there is worry as to the possible evolutio n of ENPV towards highly epidemic and pathogenic strains. This is leading t hose laboratories involved in poliomyelitis surveillance not only to search for remaining wild poliovirus strains but also to study the possible long- term circulation of OPV strains and to develop efficient ENPV surveillance.