Streptococcus suis is an encapsulated, Gram-positive, beta haemolytic bacterium and one of the most important bacterial pathogens in the porcine industry, contributing to significant economic losses and health problems in the processing of swine (Gottschalk et al., 2010). Furthermore, this pathogen is a public health risk due to its high zoonotic ability (Gottschalk et al., 2019). S. suis is considered an occupational disease in most western countries that affects individuals employed in the pig or pork industry (Takeuchi et al., 2017). In Southeast Asian nations, the general population is at risk, often due to close contact with livestock or the consumption of raw pork products (Okura et al., 2016).
Figure 1: Transmission pattern of Streptococcus suis
S. suis strains were once divided into 35 serotypes based on their distinct capsular polysaccharides(CPS), the outermost layer of the bacterial cell. A few of the old serotypes (20, 22, 26, 32, 33, and 34) are now reclassified by phylogenic and genomic sequences, either in other bacterial genera or in other Streptococcus organisms. This has decreased the number to 29. The distribution of these 29 serotypes may vary depending on the geographical region (Goyette-Desjardins et al., 2014; Gottschalk et al., 2019). S. suis serotypes 2, 9, and 3 are predominant in Europe and Asia (Prufer et al., 2019). Multiple serotypes of S. suis have been reported in diseased pigs in North America, such as serotypes 2, 3, 1/2, 8, 4 and 7 (Denich et al., 2020). S. suis serotype 2 is considered to be the most virulent, an important emerging zoonotic agent and most frequently isolated from clinical specimens and associated with disease in pigs in most countries (Gottschalk et al., 2010; Goyette-Desjardins et al., 2014). Cultural variations between Asian and Western countries are likely to influence the epidemiology of S. suis, including lifestyle; widespread use of backyard production systems; close interaction between humans and pigs; and common practice in the consumption of raw pork products in countries such as Vietnam, Laos, and Thailand (Suankratay et al., 2004; Navacharoen et al., 2009; Ho et al., 2011).