Salmonellacidal antibody response to Salmonella enterica serovar Typhi in enteric fever and after vaccination with Vi capsular polysaccharide

Objectives: Serum salmonellacidal (bactericidal) antibody could be used to detect functional capacity of antibody in patients with enteric fever and after typhoid vaccination.

Methods: Salmonellacidal antibody response was measured by colorimetric serum salmonellacidal assay from 70 acute and 11 convalescence sera of patients infected with Salmonella Typhi and Paratyphi A and also from 15 control and 6 Vi capsular polysaccharide vaccinated volunteer's sera.

Results: Sera from patients with typhoid and paratyphoid A showed significant (p < 0.05) levels of salmonellacidal antibody titer (549.9 ± 108.5 and 528.7 ± 187.3) compared with control (0.133 ± 0.1). Moreover, this titer increased significantly (p <0.05) in sera collected between 7 and 10 days and between 11 and 25 days of fever (titer 535.7 ± 119.2 and 794.6 ± 235.6) compared with sera collected from patients with fever for less than 7 days (136.4 ± 52.7). The mean titer significantly (p < 0.05) decreased to 5.5 ± 2.1 after 6-8 weeks onset of illness. Although, very low salmonellacidal titers (2.5 ± 1.5 and 2.3 ± 1.5) were detected after Vi CPS vaccine among the human volunteers, but mean titer was raised 15-fold from pre- to postvaccinated sera (0.166-2.5).

Conclusion: The serum salmonellacidal antibody by colorimetric salmonellacidal assay could be used to detect acute typhoidal cases and also to monitor immune response of typhoid vaccine.