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

During the past 40 years, around 100 cases of human S. suis infections were estimated in European countries. Among them, the top three countries in the history of human SS2 infections recorded are Netherlands (41 cases), United Kingdom (15 cases), and Denmark (12 cases). 2 The rest of the European countries (such as France and Germany) had less than ten sporadic cases of human infection. 2 Moreover, the prevalent type of clinical disease caused by S. suis infections in these countries is bacterial meningitis. Although human S. suis infections are considered sporadic cases in most countries, 2, 5, 8 it is unbelievable that its zoonotic infectious events are rarely reported in North America (Canada and USA), two huge countries with numerous, large, and frequent swine operations. 3, 5 To the best of our knowledge, only three human SS2 meningitis cases were confirmed in USA, 49, 50, 89 and three cases were diagnosed in Canada (one case was due to SS14, and the other 2 cases were caused by SS2 51, 52 ). Gottschalk and coworkers 3 believe that this small number of reported cases from these two huge countries with a big industry for pig cultivation might be attributed to the following two major reasons: (1) Clinical under-diagnosis and/or misdiagnosis of S. suis infection, rather than true absence of this infectious disease, (2) S. suis isolates in North America are less virulent, relative to those from Europe and Asia. A pilot study conducted by Smith et al. 90 recently indicated that human infection with S. suis is more common in the United States than what it is generally thought. The reason might lie in underdiagnosis or misdiagnosis, rather than a real lacking of disease. 3, 91, 92 On this issue, we doubt the current situation of S. suis infections as well, though we agree that good hygiene conditions and prevention strategies during the whole process of pork operation (e.g., wearing gloves) might secure the major route of bacterial entry into blood by small cuts in the skins, and greatly decrease the incidents of S. suis infections in North America. Therefore, we believe that it is necessary to employ combined specific approaches (like multiplex PCR plus ELISA) for the re-evaluation of the epidemiological aspects of human S. suis infections in North America. Interestingly, Schmid et al. 93 recently demonstrated that American SS2 isolates do not carry 89K PAI, a DNA fragment present in Chinese epidemic strain, which might be helpful for development of an American SS2 strain-specific PCR detection assay.