Role of enterovirus 71 in acute flaccid paralysis after the eradication of poliovirus in Brazil.

As a result of the successful initiative to eradicate poliomyelitis in the Americas, Brazil is now free of circulating wild poliovirus. The last cases of acute flaccid paralysis (AFP) with confirmed wild poliovi-rus isolation occurred in March 1989 (1). Since the elimination of wild poliovirus-associated poliomy-elitis in Brazil and the American region by intensive mass vaccination campaigns, acute paralytic illnesses from other causes constitute a greater proportion of suspected cases. Enterovirus 71 (EV71) can cause paralytic disease with persistent flaccid paralysis (which may be confused with paralysis caused by wild polioviruses); therefore, the presence of this enterovirus in a community may complicate the evaluation of poliomyelitis control progress. Se-rologic evidence of EV71 infections (demonstrated by neutralization assays) has been observed in AFP patients in Brazil (9). In addition, EV71 isolates have been obtained from patients with suspected cases of poliomyelitis and their healthy contacts from different areas in Brazil and from AFP patients in Peru and Bolivia (3, Ferreira et al., in preparation). EV71, the most recently recognized human en-terovirus in the family Picornaviridae, has been associated with outbreaks of hand-foot-and-mouth disease and central nervous system diseases (e.g., aseptic meningitis, encephalitis, and poliomyelitis-like paralytic diseases) with persistent or transient paralysis (2,4,5). Despite some understanding of the variability in clinical manifestations and epidemio-logic pattern, little is known about the contribution of EV71 to overall AFP in different countries. Immunoglobulin M (IgM) antibody to EV71 was measured by using an µ-capture enzyme immunoas-say (EIA) (6). The antigen was prepared from the BrCr strain of EV71, and biotinylated anti-EV71 monoclonal antibody as detector was also prepared (6). The results were expressed as the difference in mean optical density values measured in triplicate wells of positive antigen (P) and negative controls (N). A specimen was considered positive if the observed P-N was > 2 standard deviations (SD) above the mean of the optical densities for the negative control serum (P-N > 0.25). Serum samples were obtained from 92 infants from different regions of Brazil who had suspected poliomyelitis and symptoms of AFP during 1989 and 1990. The 138 samples included paired serum samples (S1 and S2) from 46 patients (92 sera) and 46 serum samples (S1 only) from 46 patients. Acute-phase serum samples (S1) were obtained 1 to 15 days after the onset of symptoms, and a second group of samples were obtained (S2) 15 to 45 days later; all were from children whose …