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Diversity of emm sequence types in group A beta-haemolytic streptococci in two remote Northern Territory Indigenous
Leisha J Richardson1, Rebecca J Towers, Allen C Cheng
1Menzies School of Health Research, Charles Darwin University, Darwin, Northern Territory, Australia.
Abstract:
There is a high burden of disease due to group A streptococcus (GAS) in remote Northern Territory (NT) Indigenous communities. A proposed 26-valent GAS M-type vaccine covers 80-90% of pharyngeal and invasive isolates in the US. We examined the diversity and distribution of emm types in two remote Indigenous communities in the NT Top End over a 17-year period and compared them to the proposed vaccine types. Eighty emm types were identified between 1991 and 2007. Diversity in both communities was high (overall Simpson's index 0.976), but varied between communities. Prior to 2004, 71 emm types were identified and an additional 9 emm types were identified during a period of active surveillance in 2004-2005. The proposed 26-valent vaccine would be expected to cover only 20% of emm types recovered in this study. Of the 80 emm types, 16 (20%) were new sequence types identified since the last assignment of M types in 2002. The diversity of streptococcal isolates was higher than that reported from most industrialized countries, and similar to that described in several developing countries. A vaccine based on such a variable antigen is unlikely to provide effective protection in the highest risk populations.
Insights
Group A Streptococcus (GAS) causes significant disease in remote Indigenous communities. A proposed vaccine
Area of Science:
- Microbiology
- Immunology
- Public Health
Background:
- Group A Streptococcus (GAS) presents a high disease burden in remote Northern Territory (NT) Indigenous communities.
- A 26-valent GAS M-type vaccine candidate shows promise, covering 80-90% of US isolates.
Purpose of the Study:
- To investigate the diversity and distribution of GAS emm types in two remote NT Indigenous communities over 17 years.
- To compare identified emm types with those covered by the proposed 26-valent vaccine.
Main Methods:
- Longitudinal surveillance of GAS emm types from 1991 to 2007 in two NT communities.
- emm typing of GAS isolates and comparison with existing databases and vaccine targets.
Main Results:
- Eighty distinct emm types were identified, indicating high diversity (Simpson's index 0.976).
- The proposed 26-valent vaccine would cover only 20% of the identified emm types.
- Sixteen (20%) emm types were novel sequence types identified post-2002.
Conclusions:
- GAS emm type diversity in remote NT Indigenous communities is exceptionally high, exceeding that of most industrialized nations.
- The high variability of GAS emm types suggests a vaccine targeting a limited number of M types is unlikely to be effective in this high-risk population.
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