We confirmed that S. suis does present and cause illness in pig in Bali, Indonesia. Human cases confirmed in Bali Referral Hospital must have been originated from pig. Streptococcus suis meningitis is a global zoonotic community-acquired bacterial meningitis [1, 2, 4]. The bacterium is of an extra-ordinary issue in Asia as human outbreaks are related to the traditional pork consumption practices [5, 6]. The practice of consuming raw pork with raw blood delicacy is also common in Bali.
In this study, we carefully selected suspected cases, especially that of acute cases with no history of antibiotic medication. We recorded that the cases impacted in pigs under one year old. S. suis can be isolated from sick and healthy pigs at various age [16]. Clinical manifestation seems more frequent in young animals [17]. A study in Canada [18] showed that Typable S. suis isolates were more frequently isolated from pigs between five and ten weeks of age. That the ages of our cases were under one year seem to be appropriate for S. suis illness in pig.
We recorded clinical signs in our cases involving many organs, central nervous system, respiratory system, gastro-intestinal tract, urogenital, and circulatory system. Recorded clinical signs of S. suis infection in literature can be indeed multi-organ. The signs can be pyrexia, inappetence, depression, nasal discharge, dyspnea, tremors, seizures, incoordination, unusual stances (eg, dog-sitting), inability to stand, paddling, opisthotonos, convulsions, nystagmus, skin disease , swollen limbs and death [19]. In some cases, the disease goes per-acute and ended with sudden death without obvious signs [19]. Although septicemia and meningitis are known as the most striking manifestations of the disease, but endocarditis, pneumonia and arthritis have been reported [20]. In per-acute cases, pigs are often found dead with no obvious sign [20]. Other review article is also recorded that the disease syndromes caused by S. suis in swine include arthritis, meningitis, pneumonia, septicemia, endocarditis, polyserositis, abortions and abscesses [21]. In recent experimental infection, affected pigs presented clinical signs of anorexia, depression, fever, the eyes of the diseased pigs were glazed, with reddening of mucous membranes, severe nervous symptoms (incoordination, lateral prostration, paddling, opisthotonus, convulsions, lameness in posterior limbs) [22].
Our suspected cases were from all regencies in Bali Province. However, the confirmed cases were from four regencies/municipality, namely Tabanan, Denpasar, Gianyar, Karangasem. Considering that Bali is a small island with 5.600 square kilometer with high inhabitant density (http://www.baliprov.go.id/v1/geographi), and understanding the free movement of animal in the province, we assume that the disease of S. suis infection is distributed through-out the province. Counting from the total animal number, number of sick and dead animal in the presumably positive cases, morbidity, mortality, and case fatality rate (CFR) were 18.7%, 8.4%, and 44.9%, respectively. Morbidity, mortality, and CFR of S. suis in pig are variable [23]. Other data are not available on this issue in the literature survey. Therefore, we assumed that our observation on the case epidemiology is plausible.
Our microbiological data confirms the S. suis. The result of Gram staining, chain formation, and biochemical characterization shows that identified isolates were Gram (+), coccus with grape-like or short chain. All were acid slant, catalase, and lactose positive, while VP test was negative. S. suis is an encapsulated gram-positive bacterial coccus that occurs singly, frequently in pairs, or occasionally in short chains [3]. The majority of strains are alpha-hemolytic on bovine and sheep blood agar plates after 24 h of incubation at 37°C [3]. Four tests are used for a presumptive identification of S. suis, i. e. no growth in 6.5% NaCl agar, a negative Voges-Proskauer (VP) test, and production of acid in trehalose and salicin broths [18, 24]. The VP test is critical in differentiating S. suis with other Streptococcus [15].
Final confirmation was made using PCR of GDH and recN. Both gene fragments are proposed as a system for the reclassification of S. suis or as a specific PCR system for S. Suis [25, 26]. We have established the system for S. suis detection from human and animal samples in Udayana University of Bali. We have sequenced both gene fragments from three pig cases and under submission to GenBank (Acc. No. ########). Both gene fragments were homogenous to each other as well as to human isolates, which are available in GeneBank (Acc. No. MK161045-MK161054; unpublished data).
We recorded prominent histologic pictures were congestion in brain and meningitis, bronchopneumonia, myocarditis, erosion and enteritis along gastrointestinal track, hemorrhagic liver and kidney. Dominant inflammatory cell infiltration in those tissues was neutrophil. Gross and microscopic findings of S. suis are published to include one or more of fibrinous polyserositis, fibrinous or hemorrhagic bronchopneumonia, purulent meningitis, myocardial necrosis, focal myocarditis and valvular endocarditis [23]. Moreover meningoencephalitis has been a striking lesion found in China [22]. Our meningitis histology in one case (Figure 3, panel A1-2) resembles meningitis picture described by that group.
Further research is needed to elucidate the risk factor of human infection, as well as to map the distribution of S. suis in Indonesia. The fragment of GDH or recN might be used to map the infection in Indonesia. The fragment seems specific to S. suis. Moreover, the serotype of S. suis found in this study needs to be elucidated to. Human infection is mostly attributed to serotype 2 infections. Vaccine can be developed using inactivated strain to reduce economic loss as well as the risk of human infection, including national and international travelers.