GENOMIC CHARACTERIZATION OF TYPE-2 POLIOVIRUSES ISOLATED FROM VACCINE-ASSOCIATED CASES IN BRAZIL

Twenty strains of P2/Sabin-related polioviruses isolated in Brazil wer e analyzed; ten from persistent paralytic poliomyelitis cases, three f rom suspected polio cases with transient paralysis, and seven from hea lthy contacts. The serotypes of the viral isolates were identified by the neutralization test with hyperimmune equine sera. The relationship of the isolates to the P2/Sabin strain was demonstrated by molecular hybridization and polymerase chain reaction (PCR). Partial sequencing demonstrated mutations at nucleotide 481 in the 5' noncoding region an d at amino acid 143 of the capsid protein VP1 in most of these isolate s from vaccine-associated cases in Brazil. These data support previous studies on the importance of mutations at these attenuated determinan ts in the establishment of the disease. However, the existence of isol ates without mutations at these positions suggests that they are not e ssential. The results also strengthen the possibility of the participa tion of a mutation at nucleotide 398 in the establishment of the disea se, and suggest that a mutation at nucleotide 491 or 500 may also be i nvolved in this process. The isolates from healthy contacts presented the same mutations as the isolates from vaccine-associated cases with which they were in contact. This strengthens the observation that, alt hough mutations in the genome of the P2/Sabin strain are important for the establishment of the disease, host factors are also involved.