Department of Medial Microbiology and Immunology, School of Medicine, University of California Davis, Davis, CA 95616, USA.
FEMS Microbiol Rev. 2018 Jul 1;42(4):527-541. doi: 10.1093/femsre/fuy024.
Typhoid and paratyphoid fever are severe systemic infections caused by human-adapted typhoidal Salmonella serovars that are indistinguishable in their clinical presentation, but differ from human gastroenteritis caused by zoonotic non-typhoidal Salmonella serovars. Typhoidal Salmonella serovars evolved from ancestral gastrointestinal pathogens through genetic changes that supported a change in pathogen ecology. Typhoidal Salmonella serovars share virulence properties that were acquired through convergent evolution and therefore this group is not defined by the presence of shared virulence genes that are absent from non-typhoidal Salmonella serovars. One feature distinguishing typhoidal Salmonella serovars from gastrointestinal pathogens is their ability to avert the respiratory burst of neutrophils. Furthermore, typhoidal Salmonella serovars possess several mechanisms to moderate intestinal inflammation, which are absent from non-typhoidal Salmonella serovars. Collectively, these shared virulence mechanisms enable typhoidal Salmonella serovars to breach an intact mucosal barrier and reach the gall bladder, a new ecological niche that is important because chronic gall bladder carriage promotes disease transmission. Thus, the morbidity and mortality resulting from the severe systemic infection that enables typhoidal Salmonella serovars to reach the gall bladder is coupled to their capacity for infectious transmission, which is the principal driving force of natural selection directing the emergence of this pathovar.
伤寒和副伤寒是由适应人体的伤寒沙门氏菌血清型引起的严重全身感染，在临床表现上无法区分，但与由动物源非伤寒沙门氏菌血清型引起的人类肠胃炎不同。伤寒沙门氏菌血清型通过支持病原体生态系统变化的遗传变化，从祖先的胃肠道病原体进化而来。伤寒沙门氏菌血清型具有通过趋同进化获得的毒力特性，因此，该组不是通过存在非伤寒沙门氏菌血清型中不存在的共同毒力基因来定义的。将伤寒沙门氏菌血清型与胃肠道病原体区分开来的一个特征是它们能够避免中性粒细胞的呼吸爆发。此外，伤寒沙门氏菌血清型还具有几种调节肠道炎症的机制，而这些机制在非伤寒沙门氏菌血清型中不存在。这些共同的毒力机制使伤寒沙门氏菌血清型能够突破完整的黏膜屏障并到达胆囊，这是一个新的生态位，这很重要，因为慢性胆囊携带促进了疾病的传播。因此，导致伤寒沙门氏菌血清型到达胆囊的严重全身感染的发病率和死亡率与它们的传染性传播能力有关，这是自然选择的主要驱动力，促使这种变体的出现。
