Genetic analysis of wild polioviruses towards the eradication of poliomyelitis from the Western Pacific Region.

Since a laboratory network to eradicate poliomyelitis in the Western Pacific Region started in 1991, the Department of Virology II, National Institute of Infectious Diseases, has been functioning as a Regional Reference Laboratory. From 1992 to 1998, we examined 5453 stool samples collected from 3501 patients with acute flaccid paralysis in Cambodia, Vietnam, and Laos, and we isolated 392-type 1 and 10-type 3 wild polioviruses. As a result of the extensive immunization during this time in this area, the numbers of poliomyelitis cases by wild polioviruses have drastically decreased. In 1997, only nine type 1 wild polioviruses were isolated. Eight out of the nine cases were found in Cambodia, and one was in mid-Vietnam. Since then no wild polioviruses have been isolated in the Western Pacific Region for more than two years. A nucleotide sequence analysis of these 1997 isolates indicated that they all belonged to the same strain that has been prevailing in the Indochina area, suggesting the complete interruption of wild poliovirus transmission in the region.