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Asymptomatic epidemic acquisition of group A Streptococcus: antibody response to extracellular and type-specific
Insights
Asymptomatic pharyngeal Streptococcus (group A, M-11) epidemics in children were studied. Despite high antibody titers to streptolysin O and deoxyribonuclease B, no type-specific antibodies were detected, suggesting a lack of immune response during acquisition.
Area of Science:
- Microbiology
- Immunology
- Epidemiology
Background:
- Group A Streptococcus (GAS) pharyngeal infections are common.
- Asymptomatic GAS carriage can occur, but its epidemic potential is less understood.
- The role of specific antibody responses in asymptomatic GAS acquisition requires further investigation.
Purpose of the Study:
- To investigate the antibody response in institutionalized children during an epidemic of asymptomatic pharyngeal acquisition of a specific type of group A Streptococcus (M-11, T-11).
- To determine if pre-existing or developing type-specific antibodies correlate with asymptomatic GAS carriage.
- To explore the immunological basis for asymptomatic GAS epidemics.
Main Methods:
- Sera from 40 institutionalized children with asymptomatic pharyngeal GAS (M-11, T-11) acquisition were collected.
- Antibody titers to streptolysin O (ASO) and deoxyribonuclease B (anti-DNase B) were measured in acute-phase sera.
- Type-specific antibody to the M-11 strain was assayed in initial and follow-up sera.
- Comparison of antibody titers between cases and controls was performed.
Main Results:
- Children with asymptomatic GAS acquisition showed significantly higher initial titers of ASO and anti-DNase B compared to controls (P < 0.001).
- No significant rise in ASO or anti-DNase B titers was observed between acute-phase and 3-week follow-up sera.
- No detectable type-specific antibody to the M-11 GAS strain was found in any patient, either initially or eight months post-epidemic.
Conclusions:
- Asymptomatic pharyngeal acquisition of group A Streptococcus can occur in epidemic fashion.
- The absence of detectable type-specific antibodies suggests that asymptomatic GAS acquisition is not mediated by a pre-existing or rapidly developing specific immune response.
- The observed antibody response (ASO, anti-DNase B) may reflect prior exposure or non-specific immune activation rather than response to the current asymptomatic infection.
Abstract:
The antibody response of 40 institutionalized children involved in an epidemic associated with asymptomatic pharyngeal acquisition of a group A, M-11, T-11 typeable Streptococcus was studied. Titers of antibody to streptolysin O and to deoxyribonuclease B determined in sera collected from patients within two weeks of positive throat cultures were significantly higher than those in sera of controls (P smaller than 0.001). However, there was no rise in antibody titers in sera obtained from these patients after an interval of three weeks. Type-specific antibody to the group A Streptococcus (type M-11) was assayed in the sera of 24 patients. No detectable antibody activity was found either in the initial sera or in sera collected eight months after the epidemic. Thus, the asymptomatic nature of this epidemic could not be attributed to the presence of detectable type-specific antibody in this population at the time of the epidemic. These observations suggest that asymptomatic pharyngeal acquisition of group A Streptococcus may occur in epidemic fashion in certain populations and may not be associated with evidence of an antibody response to the streptococcal organism.