Streptococcus suis infection: An emerging/reemerging challenge of bacterial infectious diseases?

Feng, Youjun; Zhang, Huimin; Wu, Zuowei; Wang, Shihua; Cao, Min; Hu, Dan; Wang, Changjun

Meningitis Meningitis is medically defined as an inflammation of the lining that covers the brain and spinal cord (the meninges). 10, 16, 60 This kind of inflammation usually initiates with a brief influenza-like prodroma and results in hearing impairment or loss. 77, 175 Generally, meningitis can be grouped into two types, bacterial and non-bacterial (e.g., viral or fungal meningitis). 77 For the former, no less than 10 kinds of bacterial pathogens (such as Mycobacteria tuberculosis, Streptococcus pneumonia, and Staphylococcus aureus) have been determined as the causatives of development of human meningitis. 33, 77 Although SS2 is a swine pathogen, we have come to know that SS2 can also be a severe agent for human bacterial meningitis. 60, 88 The first case of human SS2 infection worldwide was recorded in Denmark in 1968. 1 Hui et al. declared that SS2 would be another leading cause of the so-called communityacquired meningitis, which is only inferior to M. tuberculosis and S. pneumonia. 77 A systematic survey of bacterial meningitis in Vietnamese adults recently suggested that (1) SS2 with multiple virulence factors (e.g., EPF, SLY, MRP) is the most common pathogen and (2) its mortality is relatively low (2.6%), but hearing loss occurs at high percentage (66.4%). 16 Moreover, Hoa et al. 176 addressed the antimicrobial susceptibility profile of S. suis strains from meningitis patients, an important question, using comprehensive approaches to analyze bacterial isolates in Vietnam from 1997 to 2008. As result, they found that (1) multidrug resistance in S. suis 2 causing meningitis in southern Vietnam has increased over the 11-y period studied; (2) the tet(L) carried in these bacteria is functionally expressed, and multiple other genes are probably co-expressed. 176 These findings alerted us again that it is important to minimize abuse of antibiotics in treatment of bacterial infectious diseases, and that the development of new therapeutics against SS2 infections are in great demand. Fortunately, Ho et al. 177 reported the largest prospective epidemiological survey of human SS2 meningitis in Vietnam, and pointed out that three important risk factors associated with human SS2 meningitis included (1) eating "high risk" dishes popular in southeast Asia, (2) occupational exposure to pigs and/or pork-related products, and (3) preparation of pork in the presence of skin lesions. Further investigations from the same research group demonstrated that slaughterhouse pigs are a major reservoir of SS2 that led to human infections of SS2 meningitis in southern Vietnam. 178 It highlighted (1) the importance of an improved hygiene at pork processing facilities, and (2) the necessity for education programs concerning food safety and proper handling of pork. 178 Similar findings were also noted in the Netherlands 59 and New Zealand. 86, 179 In the Netherlands, researchers have clearly indicated that the risk of developing SS2 meningitis among abattoir workers, butchers, and pig breeders are above 1000 times higher than that among persons without close contact with pigs or their unprocessed pork products. 59 To our surprise, a study performed in New Zealand revealed that a high ratio of farmers and meat inspectors in markets were sero-positive to SS2, suggesting the presence of human sub-clinical SS2 infections to a small extent. 86, 179 Septicemia Septicemia is a serious and life-threatening infection, in which a large amount of bacteria are present in t