Streptococcus suis Infections in Humans: What is the prognosis for Western countries? (Part I)

Infections caused by Streptococcus suis are an important economic problem in the swine industry. Moreover, S. suis (especially serotype 2) is an agent of zoonosis that has the potential to afflict those who are in close contact with infected pigs or pork-derived products. Although sporadic cases of S. suis infections in humans have been reported during the last 40 years, a large outbreak in China emerged in 2005. The severity of the infection in humans during the outbreak, such as clinical signs of streptococcal toxic shock syndrome, attracted much attention from the scientific community and the public press. This two-part review will focus on this organism and the infections it causes, highlighting the differences between Asian and Western countries, particularly with respect to its epidemiology. In part I, the general characteristics of the organism are reviewed, as well as the clinical characteristics associated with S. suis infection in humans, the pathogenesis of infection and associated virulence factors, and, finally, the interactions between S. suis and the host's immune system.