Genetic characterization of poliovirus isolates in Canada, 1962-1981

From 1962 to 1981, 629 poliovirus strains of human and sewage origin were assayed for genetic markers in the kinetic serum neutralization ( KSN ) and temperature marker (rct) tests. The KSN test proved to be most dependable: 97% of strains tested could be classified as either vaccine-like (VL) or non-vaccine-like ( NVL ). All but two of the 18 virus strains whose classification was inconclusive in the KSN test were further characterized by micro serum neutralization assay. The correlation between the results of the rct and KSN marker tests was not satisfactory for the characterization of poliovirus types 1 and 3. Numerous type 1 virus strains were analyzed with strain-specific monoclonal antibodies for antigenic markers and were examined in polyacrylamide gel electrophoreses for viral proteins. Whereas greater than 90% of poliovirus types 2 and 3 were found to be VL in the KSN test, 40% of type 1 isolates were classified as NVL . The latter were detected not only in the epidemics of 1962 and 1978-1979 caused by type 1 poliovirus but also were present in endemic form in the late 1960s and 1970s in various provinces. In contrast, no NVL type 2 strains were detected in any specimen, and the last type 3 NVL strains were demonstrated in 1963-1964. Thus only type 1 poliovirus appears to be endemic in Canada.