Antigenic and molecular characterization of wild type 1 poliovirus causing outbreaks of poliomyelitis in Albania and neighboring countries in 1996

Abstract

Mass vaccination has led poliomyelitis to become a rare disease in a large part of the world, including Western Europe. However, in the past 20 years wild polioviruses imported from countries where polio is endemic have been responsible for outbreaks in otherwise polio-free European countries. We report on the characterization of poliovirus isolates from a large outbreak of poliomyelitis that occurred in Albania in 1996 and that also spread to the neighboring countries of Yugoslavia and Greece. The epidemics involved 145 subjects, mostly young adults, and caused persisting paralysis in 87 individuals and 16 deaths. The agent responsible for the outbreak was isolated from 74 patients and was identified as wild type 1 poliovirus by both immunological and molecular methods. Sequence analysis of the genome demonstrated the involvement of a single virus strain throughout the epidemics, and genotyping analysis showed 95% homology of the strain with a wild type 1 poliovirus strain isolated in Pakistan in 1995. Neutralization assays with both human sera and monoclonal antibodies were performed to analyze the antigenic structure of the epidemic strain, suggesting its peculiar antigenic characteristics. The presented data underline the current risks of outbreaks due to imported wild poliovirus and emphasize the need to improve vaccination efforts and also the need to implement surveillance in countries free of indigenous wild poliovirus.

FIG. 1

(a) Distribution of confirmed cases of polio (□) and illness compatible with polio (, samples available; , samples not available) by month of onset of paralysis in Albania in 1996. The times of NIDs and mass vaccination campaigns are indicated. (b) Age distribution of patients confirmed to have polio and with illness compatible with polio in Albania in 1996.

FIG. 2

Comparison of the VP1 sequences (nucleotides [nt] 2531 to 2830) of representative wild type 1 poliovirus isolates from Albania and the Sabin and Mahoney reference strains. HaeIII restriction enzyme sites are indicated. □, HaeIII sites; ↑, new site; ↓, suppressed site.

FIG. 3

Sequence alignment of the VP1-2A junction of wild type 1 poliovirus strains from Albania isolated in different months during the epidemics, wild type 1 strains isolated in Yugoslavia and Greece, and Sabin and Mahoney reference strains. The strains 1yug96 (Kosovo, Yugoslavia), 50940gre96 (Attica, Greece), 50968gre96 (Attica, Greece), 51268gre96 (Crete, Greece), 7gre96 (Thessalonica, Greece), and 10gre96 (Thessalonica, Greece) were from the regions indicated in parentheses.

FIG. 4

Dendrogram summarizing sequence relatedness among wild type 1 polioviruses isolated in Albania, Yugoslavia, and Greece and recent wild type 1 polioviruses isolated worldwide across the interval from nucleotides 3216 to 3445 (VP1-2A region). The PHYLIP distance method (University of Washington) was used.