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

Geographic distribution of human SS2 infections As a swine pathogen, S. suis was first reported by a vegetarian in 1954, 2 while its zoonotic role could be traced to a human SS2 meningitis case in Denmark, in 1968. 1 In light of the available literature with human S. suis infection recorded thus far, we expect that S. suis infections have been involved in no less than 30 countries and/or regions (Fig. 1) , and resulted in around 1600 cases of severe human infections. 2, 8, 48 In North America (United States 49, 50 and Canada 51, 52 ) and the South American countries (Argentina, 53, 54 Chile, 55 58 Belgium, 3 Poland, 61 Sweden, 3 Denmark, 1 Germany, 62 Hungary, 3 Austria, 63 Croatia, 64 Italy 65-67 , Greece, 68 and Portugal 1 ), some Asian countries (Laos, 1 Singapore, 33, 69 India, 2,3,70 Korea, [71] [72] [73] Japan, 74 Hong Kong, [75] [76] [77] [78] [79] [80] Taiwan, 33, 81, 82 and Philippine 2,3 ), Australia, 83, 84 and New Zealand. 85, 86 So far, endemics of human SS2 infections was only observed in two Asian counties Vietnam 2,7,16,37,38 and Thailand. 6, 11, 14, 87 Of particular note, coexistence of sporadic cases and epidemics of human SS2 infections were present in China. 4, 8, 9, [17] [18] [19] 33, 48 It seemed true that the majority of human SS2 infection cases occurred in southeast Asia (especially Vietnam, Thailand, and China), indicating an obvious geographic tropism (Fig. 1) . Although we are not quite sure what mechanism can explain such kind of tropism, we anticipate that the following factors are probably correlated with frequent occurrence of human SS2 infections in above countries, which include (1) similar local climates and/or environments; (2) backyard cultivation of pigs; and (3) popular consumption of raw pork sold in the wet market.