It caused a small outbreak in Jiangsu Province in 1998 and then, most recently, the largest outbreak in Sichuan Province in 2005 (9, 10). The ST7 S. suis strain has not been isolated outside of China. In the present study, our results indicate that four of the five MLVA types identified among the 1998 isolates of ST7 S. suis BVD-523 molecular weight were also detected in Sichuan in 2005. This suggests the pathogens responsible for the two outbreaks in China in 1998 and 2005 are closely associated. The one in Sichuan may have been
transmitted from Jiangsu province (9). In regard to the S. suis outbreak surveillance and investigations, because all of the ST7 isolates showed identical PFGE restriction patterns, we could not determine the transmission route from the PFGE data. The MLVA method described here has a higher discriminative typing power than PFGE (9). Therefore the MLVA scheme may better enable identification of transmission routes. During the outbreak in 2005, our epidemiology team found that one patient had become ill after slaughtering a diseased pig. The patient died RG7204 in vivo 18 hr after the onset of the illness (9, 26). No samples were left from the diseased pig that he had processed. However one strain (SC16) from a diseased pig in the same herd and strain SC22
isolated from the patient (9) were both typed as MLVA16. Our data supports the epidemiological observations and may confirm the transmission route. The MLVA analysis was consistent with the results of investigations suggesting that the S. suis in Jiangxi province was derived from the outbreak in Jiangsu province in 2005 (9, 10). One patient had become ill after processing pork in a cold storage house. A strain named JX1 was isolated from this patient. Three other strains, Jxs1, Jxs2 and Jxs3, were isolated from pork in the cold storage house (9). All of these Rapamycin four strains were typed as MLVA31 and a retrospective investigation found that the pork had been transported from Jiangsu province. Interestingly, three strains in
1998 and one strain in 2005 (both from Jiangsu province) were also typed as MLVA31. These data suggest the ST7 S. suis in Jiangxi province could have been derived from Jiangsu province via the pork trade (Fig. 2) (9, 10). To our knowledge, this is the first report of applying the MLVA method to S. suis. The MLVA developed here shows many advantages. First, it has a greater power to distinguish serotype 2 strains than PFGE and this makes it more useful for epidemiological purposes. Second, the MLVA method is a high-throughput screening method which is comparatively inexpensive, easy to perform, rapid, and reliable (19, 27, 28). The method is well suited for inter-laboratory comparisons of S. suis outbreak investigations. Third, reference strains are not required to ascertain consistency between inter-laboratory results (24).