Age-Specific Prevalence of Serum Antibodies to the Invasion Plasmid and Lipopolysaccharide Antigens of Shigella Species in Chilean and North American Populations

Shigella species have virulence plasmids that encode outer membrane proteins (invasion plasmid antigens, Ipa) associated with pathogenicity. Western blots were used to detect antibodies to Ipa in sera from 390 Chilean children, and these responses were compared with those of a US population of infants and adults. Antibodies to lipopolysaccharide (LPS) of Plesiomonas shigelloides and Shigella fiexneri 2a were measured by ELISA. Among the Chileans, there was an age-related acquisition of Ipa antibodies, with 28% of 1-year-olds and 100% of children ⩾ 10 years showing positive responses. In contrast, none of the US infants and only 38% of the adults had antibodies to Ipa. Levels of LPS antibodies were also found to increase in an age-related manner among the Chileans. These results corroborate findings of previous epidemiologic studies which show that Shigella infections are endemic in Chile, as in other developing countries. The measurement of Ipa and LPS antibodies is a useful seroepidemiologic tool for investigating previous exposure to Shigella species in populations.