Genetic analysis of wild polioviruses and its ecology

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Po1iovirus is a typical enterovirus and transmits from humans to humans by fecal oral routes Human being is the only sensitive animal. If good sanitary condition is once archived and maintained big outbreak of poliomyelitis wl11 be protected. However, in order to eradicate the disease poliomyelitis, community level-extensive immunity by oral vaccination and real time clinical-and viorological surveillance are essential. World Health 0rganization launched the global eradication program in 1988.In this study, we performed the genetic analysis of the wild polioviruses which has been replaced by oral vaccine viruses in Indochina area. In l997, wild type polioviruses were isolated from one patient with acute flaccid paralysis (AFP) from Vietnam and 8 from Cambodia. They were all type I poliovirus. They were all diagnosed locally as AFP cases and their stool samples were sent to Japan. We isolated viruses, identified add performed intratypic differentation. The nucleotide sequences of their VP1 region were determined and compared with those of wild viruses previously isolated in this area.In previous years, there were several different strains of wi1d polioviruses were isolated in this region. However, the 9 strains isolated in 1997 belonged to the same group of strain. From the North Vietnam, isolated polioviruses were all vaccine derived viruses, and their number has been decreased in these three years. Those results were confirmed in Japan. In contrast, there were some discrepancy in the results obtained in South Vietnam and Japan. By the use of mouse La cells expressing polio receptor gene, polioviruses were efficiently and selectively isolated.The last case of poliomyelitis by wild poliovirus in the region is so far considered to be the one found on March l9,1997. Since then, no wild polioviruses were isolated. More extensive surveillance is necessary to certify as polio-free.