The fall and rise of Group A Streptococcus diseases

Abstract

Streptococcus pyogenes (or Group A Streptococcus, GAS) is a Gram-positive human pathogen responsible for a diverse array of superficial, invasive and immune-related diseases. GAS infections have historically been diseases of poverty and overcrowding, and remain a significant problem in the developing world and in disadvantaged populations within developed countries. With improved living conditions and access to antibiotics, the rates of GAS diseases in developed societies have gradually declined during the 20th century. However, genetic changes in circulating GAS strains and/or changes in host susceptibility to infection can lead to dramatic increases in the rates of specific diseases. No situations exemplify this more than the global upsurge of invasive GAS disease that originated in the 1980s and the regional increases in scarlet fever in north-east Asia and the UK. In each case, increased disease rates have been associated with the emergence of new GAS strains with increased disease-causing capability. Global surveillance for new GAS strains with increased virulence is important and determining why certain populations suddenly become susceptible to circulating strains remains a research priority. Here, we overview the changing epidemiology of GAS infections and the genetic alterations that accompany the emergence of GAS strains with increased capacity to cause disease.

Keywords: Necrotising facsciitis Group A Streptococcus; Streptococcus pyogenes; scarlet fever; streptococcal infections; toxic shock syndrome.

Fig. 1.

Evolutionary pathway of M1T1, emm3 and emm89 GAS strains with increased capacity to cause iGAS infections. For each example, multiple genetic events involving prophage acquisition, recombination and/or point mutations have resulted in contemporary strains with increased disease-causing capacity. Estimated dates for these events are provided for the M1T1 iGAS clone (data from [21]).

Fig. 2.

Evolutionary pathway of GAS strains with increased capacity to cause Scarlet Fever. Prophage acquisition of the superantigen SSA has resulted in contemporary strains with increased disease-causing capacity. Estimated dates for these events, which predate the scarlet fever outbreak by decades, are provided for the emm12 scarlet fever strains from Hong Kong (data from [50]).