Genomic characterization of type 3 polioviruses isolated from vaccine-associated poliomyelitis cases in Brazil.

Eight strains of P3/Sabin-related polioviruses were analyzed; four from persistent paralytic poliomyelitis cases classified as vaccine associated, one from a transient paralysis case classified as transverse myelitis, one from a transient paralysis case classified as Guillain-Barré syndrome, one from a transient facial paralysis case, and one from a healthy vaccine. The serotypes of the viral isolates were identified by the neutralization test with hyperimmune equine sera and the relationship of the isolates with the P3/Sabin strain was demonstrated by molecular hybridization of the viral RNA of the isolates with a P3/Sabin-specific probe. The P3/Sabin relationship was confirmed by PCR, using a pair of specific primers for P3/Sabin-related isolates. The available data indicate that a U-->C mutation at nucleotide 472 in the 5' noncoding region of the genome of the type 3 Sabin strain increases the neurovirulence of this strain and this mutation was observed in all type 3 isolates from vaccine-associated cases. These eight P3/Sabin-related isolates were partially sequenced in the 5' noncoding region and seven presented a U-->C mutation at nucleotide 472, except the isolate from a transient paralysis case classified as transverse myelitis, that maintained a U at nucleotide 472. Although this virus maintaining U at nucleotide 472 may not be the etiological agent of the disease, the possibility that the virus was the causative agent of the disease could not be ruled out.