Streptococcus suis infection and risk factors for mortality

Contamination of Streptococcus suis and S. suis Serotype 2 in Raw Pork and Edible Pig Organs: A Public Health Concern in Chiang Mai, Thailand

Streptococcus suis is one of the most important zoonotic pathogens causing serious diseases in both pigs and humans, especially serotype 2. In northern Thailand, there is a notable prevalence of S. suis infection in humans and transmission has occurred mainly through the consumption of raw pork products. Despite the continued practice of consuming raw pork in this region, limited data exist regarding S. suis contamination in such products. Therefore, this study aimed to assess the prevalence of S. suis and S. suis serotype 2 in retail raw pork meat and edible pig organs sold in Chiang Mai city, Thailand. A total of 200 samples, comprising raw pork meat and edible pig organs, were collected from nine fresh markets in Chiang Mai city between May and July 2023. Samples were prepared and cultured in Todd-Hewitt broth. Bacterial DNA was extracted and tested for any serotypes of S. suis and serotype 2 using loop-mediated isothermal amplification (LAMP) techniques. The study revealed contaminations of S. suis and serotype 2 at rates of 84% and 34%, respectively, with a higher prevalence observed in pig organs compared to raw pork. Both S. suis and serotype 2 were detected across all nine fresh markets investigated. The prevalence of S. suis remained consistently high throughout the study period, whereas serotype 2 showed peaks in May and July. These high rates of contamination indicate that people who consume or work in close contact with raw pork or edible pig organs are at a high risk of S. suis infection. Urgent implementation and maintenance of food safety campaigns and public health interventions are crucial for disease prevention and control.

Rapid Diagnostic of Streptococcus suis in Necropsy Samples of Pigs by thrA-Based Loop-Mediated Isothermal Amplification Assay

Streptococcus (S.) suis presents a serious threat to the pig industry as well as food safety and public health. Although several LAMP assays have been developed for the identification of S. suis, no universal assay is so far available for the field-suitable examination of clinical pig specimens. Based on the thrA housekeeping gene, a new loop-mediated isothermal amplification (LAMP) assay was developed and validated for the detection of S. suis in the brain and joints of pigs. For this LAMP assay, two different methods for the extraction of DNA from brain and joint swabs were compared. Using the LPTV boiling method, the detection limit of LAMP was 1.08 CFU/reaction, while the detection limit was 53.8 CFU/reaction using a commercial DNA extraction kit. The detection limits of thrA-LAMP in combination with the LPTV boiling method were 104-105 CFU/swab in the presence of brain tissue and 103-104 CFU/swab in the presence of joint tissue. The diagnostic quality criteria of LAMP were determined by the examination of 49 brain swabs and 34 joint swabs obtained during routine diagnostic necropsies. Applying the LPTV boiling method to brain swabs, the sensitivity, specificity, and positive and negative predictive values of thrA-LAMP were 88.0, 95.8, 95.7, and 88.5% using cultural investigation as a reference method, and 76.7, 100, 100, and 73.1% using real-time PCR as a reference method. Based on these results, the thrA-LAMP assay combined with the LPTV boiling method is suitable for rapid detection of S. suis from brain swabs.

Isopropoxy Benzene Guanidine Ameliorates Streptococcus suis Infection In Vivo and In Vitro

Streptococcus suis, an encapsulated zoonotic pathogen, has been reported to cause a variety of infectious diseases, such as meningitis and streptococcal-toxic-shock-like syndrome. Increasing antimicrobial resistance has triggered the need for new treatments. In the present study, we found that isopropoxy benzene guanidine (IBG) significantly attenuated the effects caused by S. suis infection, in vivo and in vitro, by killing S. suis and reducing S. suis pathogenicity. Further studies showed that IBG disrupted the integrity of S. suis cell membranes and increased the permeability of S. suis cell membranes, leading to an imbalance in proton motive force and the accumulation of intracellular ATP. Meanwhile, IBG antagonized the hemolysis activity of suilysin and decreased the expression of Sly gene. In vivo, IBG improved the viability of S. suis SS3-infected mice by reducing tissue bacterial load. In conclusion, IBG is a promising compound for the treatment of S. suis infections, given its antibacterial and anti-hemolysis activity.

Human Streptococcus suis Infections in Thailand: Epidemiology, Clinical Features, Genotypes, and Susceptibility

Streptococcus suis is a zoonotic pathogen causing substantial economic losses to the pig industry, as well as being a human health burden due to infections worldwide, especially in Southeast Asia. In Thailand, there was high cumulative incidence in humans during 1987-2021, mostly in males. At least five large outbreaks have been documented after the largest outbreak in China in 2005, which was related to the consumption of raw pork or dishes containing pig's blood. The major clinical features are sepsis or meningitis, with hearing loss a major complication of S. suis disease. Thai human S. suis isolates have shown diversity in serotypes and sequence types (STs), with serotype 2 and STs 1 and 104 being major genotypes. β-Lactam antibiotics can be used in empirical treatment for human S. suis infections; however, intermediate resistance to penicillin has been reported. Reducing S. suis incidence in Thailand requires a multidimensional approach, with combined efforts from the government and public health sectors through policy, regulations, education, and active surveillance.

Cross-sectional risk assessment of zoonotic Streptococcus suis in pork and swine blood in Nakhon Sawan Province in northern Thailand

A cross-sectional study evaluated the risk of zoonotic Streptococcus suis (S. suis) illness from consuming raw pork and swine blood in Nakhon Sawan Province. A four-step risk assessment recommended by the Codex Alimentarius Commission was used to evaluate the risk along the pork supply chain. A total of 480 pork and swine blood samples were collected from the abattoir (n = 120) and retail (n = 360) during December 2020 and January 2021. Streptococcus suis in samples was enumerated using a culture-based technique and then confirmed by the biochemical and molecular technique. Streptococcus suis was serotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Two positive swine blood samples were contaminated with non-zoonotic S. suis serotype 23 at retail. In the case of all negative samples, the deterministic prevalence becomes zero and then the risk could not be estimated. Otherwise, the beta probability distribution was used to describe the probabilistic prevalence, while the maximum likelihood estimator was applied to estimate the upper limit of a probability distribution of concentration. The district averages of probabilistic prevalences of zoonotic S. suis in pork products at abattoir and retail were 9.9% and 4.1%, respectively. The district averages of concentrations of zoonotic S. suis in pork and blood samples from abattoir were 6.8 × 10^-3  cfu/g and 6.83 cfu/ml and in pork and blood samples from retail were 2.3 × 10^-3  cfu/g and 2.30 cfu/ml, respectively. The overall annual risk estimate per 100,000 population in pork and swine blood from abattoir and retail were 9.8 × 10^-11 , 2.2 × 10^-6 , 5.4 × 10^-13 , and 8.3 × 10^-8 . These risk estimates were negligible (<10^-6 ) except for the annual risk estimate in swine blood from the abattoir. The results from this cross-sectional risk assessment should prompt the food safety regulator to cautiously sample by taking into account the duration of sampling and sample size.

Clinical and Epidemiological Characteristics of Streptococcus suis Infections in Catalonia, Spain

Introduction:Streptococcus suis (S. suis) is a human zoonotic pathogen of occupational origin, with infection acquired through contact with live pigs or pig meat. Pig farming is one of Catalonia's biggest industries and as a result this region of Spain has one of the highest density pig populations per km². The aim of our study was to describe the infections caused by S. suis occurring in that area over a 9-year period.

Materials and Methods: A retrospective, multi-center study was carried out by searching records from 15 hospitals in Catalonia for the period between 2010 and 2019.

Results: Over the study period altogether nine cases of S. suis infection were identified in five hospitals, with five of these cases occurring in the 2018–2019 period. The mean age of patients was 48 ± 8.9 years and all of them were males. Five patients (55.6%) worked in pig farms. The most frequent manifestation of infection was meningitis (5 cases; 55.6%) followed by septic arthritis (3 cases; 33.3%). None of the patients died at 30 days; nonetheless, 4 developed hearing loss as a long-term complication.

Conclusion: The most commonly identified S. suis infection was meningitis. Over 50% of the episodes occurred in the last 2 years and have affected pig farm workers. Further surveillance is needed in order to know its prevalence.

Burden of disease and productivity impact of Streptococcus suis infection in Thailand

Background

Streptoccocus suis (S.suis) infection is a neglected zoonosis disease in humans mainly affects men of working age. We estimated the health and economic burden of S.suis infection in Thailand in terms of years of life lost, quality-adjusted life years (QALYs) lost, and productivity-adjusted life years (PALYs) lost which is a novel measure that adjusts years of life lived for productivity loss attributable to disease.

Methods

A decision-analytic Markov model was developed to simulate the impact of S. suis infection and its major complications: death, meningitis and infective endocarditis among Thai people in 2019 with starting age of 51 years. Transition probabilities, and inputs pertaining to costs, utilities and productivity impairment associated with long-term complications were derived from published sources. A lifetime time horizon with follow-up until death or age 100 years was adopted. The simulation was repeated assuming that the cohort had not been infected with S.suis. The differences between the two set of model outputs in years of life, QALYs, and PALYs lived reflected the impact of S.suis infection. An annual discount rate of 3% was applied to both costs and outcomes. One-way sensitivity analyses and Monte Carlo simulation modeling technique using 10,000 iterations were performed to assess the impact of uncertainty in the model.

Key results

This cohort incurred 769 (95% uncertainty interval [UI]: 695 to 841) years of life lost (14% of predicted years of life lived if infection had not occurred), 826 (95% UI: 588 to 1,098) QALYs lost (21%) and 793 (95%UI: 717 to 867) PALYs (15%) lost. These equated to an average of 2.46 years of life, 2.64 QALYs and 2.54 PALYs lost per person. The loss in PALYs was associated with a loss of 346 (95% UI: 240 to 461) million Thai baht (US$11.3 million) in GDP, which equated to 1.1 million Thai baht (US$ 36,033) lost per person.

Conclusions

S.suis infection imposes a significant economic burden both in terms of health and productivity. Further research to investigate the effectiveness of public health awareness programs and disease control interventions should be mandated to provide a clearer picture for decision making in public health strategies and resource allocations.

Streptoccocus suis (S.suis) infection is a potentially lethal zoonotic disease in humans. In the present study, we sought to estimate the impact of the disease in Thailand in terms of years of life lost, quality-adjusted life years (QALYs) lost, and productivity-adjusted life years (PALYs) lost. A decision-analytic Markov model was developed to simulate the impact of S.suis infection and its major complications among Thai people. In 2019, it was estimated that the infection incurred 769 years of life lost (14% of predicted years of life lived if infection had not occurred), 826 QALYs lost (21%) and 793 PALYs (15%) lost. These equated to an average of 2.5 years of life, 2.6 QALYs and 2.5 PALYs lost per person. The loss in PALYs was associated with a loss of 346 million Thai baht (US$11.3 million) in GDP, which equated to 1.1 million Thai baht (US$ 36,033) lost per person. The findings call for increased public health awareness and comprehensive efforts to control and prevent the disease.

Streptococcus suis: An Underestimated Emerging Pathogen in Hungary?

Streptococcus suis (S. suis) is an emerging zoonotic pathogen, demonstrated as an etiological agent in human infections in increasing frequency, including diseases like purulent meningitis, sepsis, uveitis-endophtalmitis and arthritis. Due to the increased availability and utility of novel diagnostic technologies in clinical microbiology, more studies have been published on the epidemiology of S. suis, both in veterinary and human medicine; however, there are no comprehensive data available regarding human S. suis infections from East-Central European countries. As a part of our study, data were collected from the National Bacteriological Surveillance (NBS) system on patients who had at least one positive microbiological result for S. suis, corresponding to an 18-year study period (2002-2019). n = 74 S. suis strains were isolated from invasive human infections, corresponding to 34 patients. The number of affected patients was 1.89 ± 1.53/year (range: 0-5). Most isolates originated from blood culture (63.5%) and cerebrospinal fluid (18.9%) samples. Additionally, we present detailed documentation of three instructive cases from three regions of the country and with three distinctly different outcomes. Hungary has traditional agriculture, the significant portion of which includes the production and consumption of pork meat, with characteristic preparation and consumption customs and unfavorable epidemiological characteristics (alcohol consumption, prevalence of malignant diseases or diabetes), which have all been described as important predisposing factors for the development of serious infections. Clinicians and microbiologist need to be vigilant even in nonendemic areas, especially if the patients have a history of occupational hazards or having close contact with infected pigs.

A risk scoring system for predicting Streptococcus suis hearing loss: A 13-year retrospective cohort study

BACKGROUND

Streptococcus suis (S.suis) is an emerging zoonosis disease with a high prevalence in Southeast Asia. There are over 1,500 cases reported globally in which majority of cases are from Thailand followed by Vietnam. The disease leads to meningitis in human with sensorineural hearing loss (SNHL) as the most common complication suffered by the patients. Early diagnosis and treatment is important to prevent severe neurological complication. In this study, we aim to develop an easy-to-use risk score to promote early diagnosis and detection of S.suis in patients who potentially develop hearing loss.

METHODS

Data from a retrospective review of 13-year S.suis patient records in a tertiary hospital in Chiang Mai, Northern, Thailand was obtained. Univariate and multivariate logistic regressions were employed to develop a predictive model. The clinical risk score was constructed from the coefficients of significant predictors. Area under the receiver operator characteristic curve (AuROC) was identified to verify the model discriminative performance. Bootstrap technique with 1000-fold bootstrapping was used for internal validation.

KEY RESULTS

Among 133 patients, the incidence of hearing loss was 31.6% (n = 42). Significant predictors for S. suis hearing loss were meningitis, raw pork consumption, and vertigo. The predictive score ranged from 0-4 and correctly classified 81.95% patients as being at risk of S.suis hearing loss. The model showed good power of prediction (AuROC: 0.859; 95%CI 0.785-0.933) and calibration (AuROC: 0.860; 95%CI 0.716-0.953).

CONCLUSIONS

To our best knowledge, this is the first risk scoring system development for S.suis hearing loss. We identified meningitis, raw pork consumption and vertigo as the main risk factors of S.suis hearing loss. Future studies are needed to optimize the developed scoring system and investigate its external validity before recommendation for use in clinical practice.

Clinical Manifestations and Risk Factors of Streptococcus suis Mortality Among Northern Thai Population: Retrospective 13-Year Cohort Study

Purpose

Streptococcus suis (S. suis) is an emerging zoonotic disease mainly in pigs, causing serious infections in humans with high prevalence in Southeast Asia. Despite a relatively high mortality rate, there are limited data regarding the risk factors of this life-threatening infection. Therefore, a 13-year retrospective cohort study in Chiang Mai, Thailand during 2005-2018 was conducted to explore risk factors associated with S. suis mortality and to update the outcomes of the disease.

Patients and methods

S. suis positive cases were derived from those with positive S. suis isolates from microbiological culture results and Matrix-Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF). Potential risk factors of mortality were identified using univariate and multivariate logistic regression.

Results

Of 133 patients with culture-proven S. suis infection identified, there were 92 males and 41 females. The mean age was 56.47 years. Septicemia (55.64%) was the most common clinical manifestation followed by meningitis (37.59%) and infective endocarditis (25.56%). Alcohol drinking and raw pork consumption were documented in 66 (49.62%) and 49 (36.84%) cases respectively. The overall mortality rate was 12.03% (n=16). According to the multivariate analysis, the independent risk factors for mortality were prolonged bacteremia ≥ 6 days (OR = 43.57, 95% CI = 2.46-772.80, P =0.010), septic shock (OR = 13.34, 95% CI = 1.63-109.03, P =0.016), and direct bilirubin > 1.5 mg/dL (OR = 12.86, 95% CI = 1.91-86.59, P =0.009).

Conclusion

S. suis is not infrequent in Northern Thailand, where the cultural food habit of raw pork eating is still practiced. To the best of our knowledge, this is the largest series focusing on risk factors of S. suis mortality which has been conducted in Thailand. Prolonged bacteremia ≥ 6 days, septic shock, and direct bilirubin > 1.5 mg/dL were strong predictors associated with S. suis mortality. The mortality risk factors identified may be further utilized in clinical practice and future research to improve patient outcomes.

Culture-Negative Streptococcus suis Infection Diagnosed by Metagenomic Next-Generation Sequencing

Background:Streptococcus suis is a zoonotic pathogen that can cause severe infections such as meningitis and septicemia in both swine and humans. Rapid and accurate identification of the causative agent is very important for guiding clinical choices in administering countermeasures.

Case Report: Here, we report a case of fatal S. suis infection in a patient who worked as a butcher in China. The 59-year-old man, who had previously undergone splenectomy, injured his finger while processing pork and developed severe sepsis. While blood cultures were negative following antibiotic treatment, S. suis was determined to be the causative agent by metagenomic next-generation sequencing (mNGS) and Sanger sequencing.

Conclusion: Identification of etiological agents using techniques such as blood culture prior to antibiotic treatment is very important. mNGS may represent a useful method for diagnosis of infectious diseases, especially post-antibiotic treatment.

Streptococcus suis-Associated Meningitis, Bali, Indonesia, 2014-2017

Streptococcus suis is an emerging agent of zoonotic bacterial meningitis in Asia. We describe the epidemiology of S. suis cases and clinical signs and microbiological findings in persons with meningitis in Bali, Indonesia, using patient data and bacterial cultures of cerebrospinal fluid collected during 2014-2017. We conducted microbiological assays using the fully automatic VITEK 2 COMPACT system. We amplified and sequenced gene fragments of glutamate dehydrogenase and recombination/repair protein and conducted PCR serotyping to confirm some serotypes. Of 71 cases, 44 were confirmed as S. suis; 29 isolates were serotype 2. The average patient age was 48.1 years, and 89% of patients were male. Seventy-seven percent of patients with confirmed cases recovered without complications; 11% recovered with septic shock, 7% with deafness, and 2% with deafness and arthritis. The case-fatality rate was 11%. Awareness of S. suis infection risk must be increased in health promotion activities in Bali.

Review of Biological and Chemical Health Risks Associated with Pork Consumption in Vietnam: Major Pathogens and Hazards Identified in Southeast Asia

Foodborne illness is a difficult public health burden to measure, with accurate incidence data usually evading disease surveillance systems. Yet, the global scope of foodborne disease and its impacts on socioeconomic development make it an important health risk to address, particularly in low- and middle-income countries. In Vietnam, rapid development has seen large-scale commercial operations rise to coexist amongst traditional value chains in the food landscape, most of which operates outside of a domestic food safety network. Rapid socioeconomic development has also seen an increase in meat consumption, with pork being the most consumed meat product nationally. Expanding pork value chains, and the increasing diversity of actors within them, facilitates the growth and propagation of hazards which are passed onto Vietnamese consumers. In order to guide illness prevention and governance efforts, this review was conducted to examine health risks associated with pork consumption in Vietnam. Synthesis of the available literature provided evidence that Salmonella spp. bacteria are a major cause of foodborne illness from Vietnamese pork products. However, contaminants of global concern, including Salmonella spp. and Trichinella spiralis, occur alongside those considered neglected tropical diseases, such as Taenia solium. Infections and complications associated with ingestion of Streptococcus suis bacteria are also an issue, with Streptococcus suis infections usually limited to occupational infections amongst meat handlers in modernised value chains. A risk factor underscoring transmission of Trichinella spiralis, Taenia solium, and Streptococcus suis in Vietnam that emerges from the literature is the consumption of dishes containing raw or undercooked pork. Available data indicates that infections associated with raw pork consumption disproportionately affect men and people in regional mountainous areas of northwest Vietnam, where many of Vietnam’s ethnic minority communities reside. In addition, epidemiological data from recorded disease outbreaks that result from raw pork consumption demonstrate that these outbreaks usually follow major sociocultural events such as weddings, funerals, and Lunar New Year celebrations. Potential health impacts resulting from residues of antibiotics and heavy metals are also cause for concern, though the direct links between chemical contaminants in food and the development of disease are difficult to conclusively deduce.

Risk factors for Streptococcus suis infection: A systematic review and meta-analysis

Streptococcus suis (S. suis) is a gram-positive bacterial pathogen in pigs which can cause serious infections in human including meningitis, and septicaemia resulting in serious complications. There were discrepancies between different data and little is known concerning associated risk factors of S. suis. A systematic review and meta-analysis was conducted to investigate on S. suis infection risk factors in human. We searched eight relevant databases using the MeSH terms "Streptococcus suis" OR "Streptococcus suis AND infection" limited in human with no time nor language restriction. Out of 4,999 articles identified, 32 and 3 studies were included for systematic review and meta-analysis respectively with a total of 1,454 Streptococcus suis cases reported. S. suis patients were generally adult males and the elderly. The mean age ranged between 37 to 63 years. Meningitis was the most common clinical manifestation, and deafness was the most common sequelae found among survivors followed by vestibular dysfunction. Infective endocarditis was also noted as among the most common clinical presentations associated with high mortality rate in a few studies. Meta-analyses categorized by type of control groups (community control, and non-S. suis sepsis) were done among 850 participants in 3 studies. The combined odd ratios for studies using community control groups and non-S. Suis sepsis as controls respectively were 4.63 (95% CI 2.94-7.29) and 78.00 (95% CI 10.38-585.87) for raw pork consumption, 4.01 (95% CI 2.61-6.15) and 3.03 (95% CI 1.61-5.68) for exposure to pigs or pork, 11.47, (95% CI 5.68-23.14) and 3.07 (95% CI 1.81-5.18) for pig-related occupation and 3.56 (95% CI 2.18-5.80) and 5.84 (95% CI 2.76-12.36) for male sex. The results were found to be significantly associated with S. suis infection and there was non-significant heterogeneity. History of skin injury and underlying diseases were noted only a small percentage in most studies. Setting up an effective screening protocol and public health interventions would be effective to enhance understanding about the disease.

Defining the taxonomic status of Streptococcus suis serotype 33: the proposal for Streptococcus ruminantium sp. nov

To clarify the taxonomic classification of Streptococcus suis serotype 33, we performed biochemical and molecular genetic analyses using isolates (GUT-183, GUT-184, GUT-185, GUT-186, GUT-187T, GUT-188, GUT-189, GUT-190, GUT-191, GUT-192 and GUT-193) from bovine endocarditis. A comparative sequence analysis showed 99.2-100 % sequence similarity among the reference strain of S. suis serotype 33 and our isolates for the 16S rRNA gene. These similarities were higher than those between the isolate GUT-187T and S. suis and other streptococci. Comparison of sodA genes also showed high degrees of similarities among the reference strain of S. suis serotype 33 and our isolates (99.7-100 %), which were higher than those between the GUT-187T and S. suis and other streptococci. DNA-DNA relatedness among three isolates (GUT-186, GUT-187T, the reference strain of S. suis serotype 33) was over 76.7 %. In contrast, the relatedness between GUT-187T and the other streptococcal species (S. suis, Streptococcus parasuis, Streptococcus acidominimus and Streptococcus porci) was 8.4-24.9 %. Phylogenetic analyses showed that the isolates did not affiliate closely to any known species of the genus Streptococcus. Moreover, GUT-187T could be distinguished from S. suis and other closely related species of genus Streptococcus using biochemical tests. On the basis of the phenotypic and molecular genetic data, we propose that the isolates of S. suis serotype 33 should be classified into the genus Streptococcus, Streptococcus ruminantium sp. nov. with the type strain GUT-187T (=DSM 104980T=JCM 31869T).

Impact of a Food Safety Campaign on Streptococcus suis Infection in Humans in Thailand

AbstractStreptococcus suis is an important zoonotic pathogen in swine and humans that causes sepsis and meningitis. Our previous study in Thailand showed that the prevalence of S. suis infection in humans, especially in northern areas of Thailand, and the transmission of the pathogen occurred mainly through the consumption of traditional raw pork products. Considering the high incidence proportion and mortality rate of the disease as an important public health problem, we implemented a food safety campaign in the Phayao Province in northern Thailand in 2011. We evaluated the effects of a food safety campaign by comparing the sociodemographic, clinical, and bacteriological characteristics of cases before and after the campaign. The follow-up study showed a marked decrease of the incidence proportion in the first 2 years, indicating the effectiveness of the campaign. In the third year, however, the incidence proportion slightly increased again, indicating the existence of deep-rooted cultural behaviors and the necessity of continuous public health intervention. Furthermore, epidemiological analysis of the cases made it possible to estimate the infectivity of the pathogen via the oral route of infection. In the present study, we showed the effectiveness of the food safety campaign for controlling the S. suis infection, and we present a role model public health intervention for prevalent areas affected by S. suis infection in humans.

Streptococcus suis Meningitis: A Systematic Review and Meta-analysis

Background

Streptococcus suis is the most common cause of meningitis in pork consuming and pig rearing countries in South-East Asia. We performed a systematic review of studies on S. suis meningitis to define the clinical characteristics, predisposing factors and outcome.

Methodology

Studies published between January 1, 1980 and August 1, 2015 were identified from main literature databases and reference lists. Studies were included if they were written in West-European languages and described at least 5 adult patients with S. suis meningitis in whom at least one clinical characteristic was described.

Findings

We identified 913 patients with S. suis meningitis included in 24 studies between 1980 and 2015. The mean age was 49 years and 581 of 711 patients were male (82%). Exposure to pigs or pork was present in 395 of 648 patients (61%) while other predisposing factors were less common. 514 of 528 patients presented with fever (97%), 429 of 451 with headache (95%), 462 of 496 with neck stiffness (93%) and 78 of 384 patients (20%) had a skin injury in the presence of pig/pork contact. The case fatality rate was 2.9% and hearing loss was a common sequel occurring in 259 of 489 patients (53%). Treatment included dexamethasone in 157 of 300 (52%) of patients and was associated with reduced hearing loss in S. suis meningitis patients included in a randomized controlled trial.

Conclusion

S. suis meningitis has a clear association with pig and pork contact. Mortality is low, but hearing loss occurs frequently. Dexamethasone was shown to reduce hearing loss.

Meningitis is a common manifestation of Streptococcus suis infection. S. suis is endemic in pork consuming and pig rearing countries. We systematically reviewed the clinical characteristics, predisposing factors and outcome of S. suis meningitis. We identified 913 patients included in 24 studies, with a mean age of 49 years and a majority of male patients (82%). Exposure to pigs or pork was present in 61%, with a skin injury being present in 20%. Fever was present in 97% of patients, headache in 95%, neck stiffness in 93%. The mortality was 2.9% and hearing loss was common occurring in 53% of patients. Dexamethasone was associated with reduced hearing loss.

Cultural drivers and health-seeking behaviours that impact on the transmission of pig-associated zoonoses in Lao People's Democratic Republic

Pig rearing is an important income source in the Lao People's Democratic Republic (PDR), with many smallholder farmers using traditional free-range pig production systems. Despite the potentially significant health risks posed by pig production regarding pig-associated zoonoses, information on the sociocultural drivers of these zoonoses is significantly lacking. This review summarises the existing sociocultural knowledge on eight pig-associated zoonoses suspected to be endemic in Southeast Asia: brucellosis, Q fever (Coxiella burnetii), trichinellosis, hepatitis E virus, leptospirosis, Japanese encephalitis, Streptococcus suis and Taenia solium taeniasis-cysticercosis. It summarises current knowledge on these diseases grouped according to their clinical manifestations in humans to highlight the propensity for underreporting. A literature search was conducted across multiple databases for publications from 1990 to the present day related to the eight pig-associated zoonoses and the risk and impact connected with them, with Lao PDR as a case study. Many of these pig-associated zoonoses have similar presentations and are often diagnosed as clinical syndromes. Misdiagnosis and underreporting are, therefore, substantial and emphasise the need for more robust diagnostics and appropriate surveillance systems. While some reports exist in other countries in the region, information is significantly lacking in Lao PDR with existing information coming mainly from the capital, Vientiane. The disease burden imposed by these zoonoses is not only characterised by morbidity and mortality, but directly impacts on livelihoods through income reduction and production losses, and indirectly through treatment costs and lost work opportunities. Other factors crucial to understanding and controlling these diseases are the influence of ethnicity and culture on food-consumption practices, pig rearing and slaughter practices, hygiene and sanitation, health-seeking behaviours and, therefore, risk factors for disease transmission. Published information on the knowledge, attitudes and beliefs of people regarding pig zoonoses and their risk factors is also extremely limited in Lao PDR and the broader Southeast Asian region. The need for more transdisciplinary research, using a One Health approach, in order to understand the underlining social determinants of health and their impacts on health-seeking behaviours, disease transmission and, ultimately, disease reporting, cannot be more emphasized.

Serotype- and virulence-associated gene profile of Streptococcus suis isolates from pig carcasses in Chiang Mai Province, Northern Thailand

In this present study, the serotype of 40 Streptococcus suis isolates from submaxillary glands of pig carcasses sold in wet markets in Chiang Mai Province, northern Thailand, was investigated. Eleven serotypes, including types 2, 3, 4, 5, 7, 8, 9, 17, 21, 22 and 31, were found in the isolates by a Multiplex PCR combined with serum agglutination. Of the eleven serotypes present, type 3 was the most prevalent, while types 2, 4, 5 and 21 were of primary interest due to their human isolate serotype. The mrp+/epf - /sly - genotype was found to be the most prevalent genotype. This study indicates the importance of effective control of human S. suis infection due to raw pork or pig carcass handling in northern Thailand.

Streptococcus suis, an important pig pathogen and emerging zoonotic agent-an update on the worldwide distribution based on serotyping and sequence typing

Streptococcus suis is an important pathogen causing economic problems in the pig industry. Moreover, it is a zoonotic agent causing severe infections to people in close contact with infected pigs or pork-derived products. Although considered sporadic in the past, human S. suis infections have been reported during the last 45 years, with two large outbreaks recorded in China. In fact, the number of reported human cases has significantly increased in recent years. In this review, we present the worldwide distribution of serotypes and sequence types (STs), as determined by multilocus sequence typing, for pigs (between 2002 and 2013) and humans (between 1968 and 2013). The methods employed for S. suis identification and typing, the current epidemiological knowledge regarding serotypes and STs and the zoonotic potential of S. suis are discussed. Increased awareness of S. suis in both human and veterinary diagnostic laboratories and further establishment of typing methods will contribute to our knowledge of this pathogen, especially in regions where complete and/or recent data is lacking. More research is required to understand differences in virulence that occur among S. suis strains and if these differences can be associated with specific serotypes or STs.

Correlation between PFGE Groups and mrp/epf/sly Genotypes of Human Streptococcus suis Serotype 2 in Northern Thailand

Streptococcus suis infection is a severe zoonotic disease commonly found in Northern Thailand where people often consume raw pork and/or pig's blood. The most frequent clinical presentations are meningitis, sepsis, and endocarditis with higher rate of mortality and hearing loss sequelae. To clarify the correlation between pulsed-field gel electrophoresis (PFGE) groups and mrp/epf/sly genotypes of S. suis serotype 2, 62 patient and 4 healthy pig isolates from Northern Thailand were studied. By PFGE analysis, at 66% homology, most human isolates (69.4%) and 1 pig isolate were in group A, whereas 14.5% of human isolates and 3 out of 4 pig isolates were in group D. According to mrp/epf/sly genotypes, 80.6% of human isolates were identified in mrp⁺epf⁻sly⁻ and only 12.9% were in mrp⁻epf⁻sly⁺ genotypes; in contrast, 1 and 3 pig isolates were detected in these two genotypes, respectively. Interestingly, all isolates of S. suis serotype 2 classified in PFGE groups A, B, and E were set in mrp⁺epf⁻sly⁻ genotypes. These data show a close correlation between PFGE groups and mrp/epf/sly genotypes of human S. suis serotype 2.

Food Safety: Emerging Pathogens

This article presents information related to emerging pathogens that are foodborne or have the potential to be foodborne including bacteria, viruses, and parasites. The phenotypic characteristics of these pathogens, their epidemiology, prevalence in foods, and transmission routes to humans as well as means for their control are also discussed.

Socio-economic, industrial and cultural parameters of pig-borne infections

The pork-processing industry has been possibly the fastest growing sector of the food industry in recent years. Specialization, genetic homogenization of the pig population, high density of the breeding population, reduced human-animal interactions, slaughter at a lower age and increased international trade of live animals and pork are parameters that affect, positively or negatively, the emergence of novel pig-borne pathogens, many of which are pig-specific, and many of which have significant zoonotic potential, as observed in recent outbreaks of Nipah virus and Streptococcus suis in Southeast Asia and China, respectively. Numerous other pathogens are transmitted to humans through direct contact with or consumption of pig products, and globalization trends in trade and human population movements have resulted in outbreaks of pig-borne diseases even in Muslim countries and in Israel, where pork consumption is religiously prohibited. The role of pigs as potential reservoirs of antibiotic-resistant pathogens or genes encoding resistance, and the role of feral pigs as a reservoir of zoonotic disease, are scientific fields in direct need of further research.

Zoonoses in South-East Asia: a regional burden, a global threat

Zoonoses are an issue of growing interest in South-East Asia, where environmental factors and socio-economic context favor the endemization of well-known diseases and the emergence of new pathogens at the human-wildlife interface. However, the health status of the region with respect to many zoonotic diseases remains poorly defined, despite the high overall burden of zoonoses on the countries of the area, and the global risk of new biological threats in the region. The first objective of this paper was to provide an update of data on the zoonoses commonly described by the scientific community and reported by governmental institutions and international organizations in continental South-East Asia. The analysis of the available data led to the identification of some trends in the evolution of the diseases, as well as some gaps in knowledge and in the current surveillance and control networks. In light of these findings, we discuss measures for effectively addressing zoonotic disease issues in South-East Asia, such as the allocation of funds for research and for surveillance and control programs, and a multi-sectoral and multi-disciplinary approach at various levels.

Severe cochlear inflammation and vestibular syndrome in an experimental model of Streptococcus suis infection in mice

Hearing impairment is a common and frequently permanent sequel of Streptococcus suis meningitis in humans. Nevertheless, mechanisms underlying the development of cochlear damage have not been addressed so far. In the present work, we characterized a mouse model of suppurative labyrinthitis and meningitis induced by a systemic infection with S. suis and studied the impact of the injected bacterial dosage on the progression of such inflammatory events. We observed that high infection doses of bacteria lead to sustained bacteremia, with an increase in the permeability of the blood-labyrinth and blood-brain barriers, causing suppurative labyrinthitis and meningitis, respectively. However, in mice infected with a low dose of S. suis, bacteria disappeared quickly from blood, hence, cochlear inflammation and meningitis were not consistent features. This model of S. suis infection seems ideal to evaluate novel drugs that may help alleviate the negative consequences of such important sequelae of S. suis-induced meningitis and labyrinthitis.

Population-based study of Streptococcus suis infection in humans in Phayao Province in northern Thailand

BACKGROUND

Streptococcus suis infection in humans has received increasing worldwide recognition.

METHODS AND FINDINGS

A prospective study of S. suis infection in humans was conducted in Phayao Province in northern Thailand to determine the incidence and the risk behaviors of the disease in this region in 2010. Thirty-one cases were confirmed. The case fatality rate was 16.1%, and the estimated incidence rate was 6.2 per 100,000 in the general population. The peak incidence occurred in May. The median age of the patients was 53 years and 64.5% were men. Consumption of raw pork products was confirmed in 22 cases and the median incubation period (range) was 2 days (0-11) after consumption of raw pork products. Isolates from 31 patients were confirmed as serotype 2 in 23 patients (74.2%) and serotype 14 in eight patients (25.8%). The major sequence types (STs) were ST1 (n = 20) for serotype 2 and ST105 (n = 8) for serotype 14. The epidemiological analysis suggested three possible clusters, which included 17 cases. In the largest possible cluster of 10 cases in Chiang Kham and its neighboring districts in May, the source of infection in four cases was identified as a raw pork dish served at the same restaurant in this district. Microbiological analysis confirmed that three of four cases associated with consumption of raw pork at this restaurant were attributable to an identical strain of serotype 2 with ST1 and pulsotype A2.

CONCLUSIONS

Our data suggest a high incidence rate of S. suis infection in the general population in Phayao Province in 2010 and confirm a cluster of three cases in 31 human cases. Food safety control should be strengthened especially for raw pork products in northern Thailand.

Comparative genomic analysis of Streptococcus suis reveals significant genomic diversity among different serotypes

Background

Streptococcus suis (S. suis) is a major swine pathogen and an emerging zoonotic agent. Serotypes 1, 2, 3, 7, 9, 14 and 1/2 are the most prevalent serotypes of this pathogen. However, almost all studies were carried out on serotype 2 strains. Therefore, characterization of genomic features of other serotypes will be required to better understand their virulence potential and phylogenetic relationships among different serotypes.

Results

Four Chinese S. suis strains belonging to serotypes 1, 7, 9 and 1/2 were sequenced using a rapid, high-throughput approach. Based on the 13 corresponding serotype strains, including 9 previously completed genomes of this bacterium, a full comparative genomic analysis was performed. The results provide evidence that (i) the pan-genome of this species is open and the size increases with addition of new sequenced genomes, (ii) strains of serotypes 1, 3, 7 and 9 are phylogenetically distinct from serotype 2 strains, but all serotype 2 strains, plus the serotype 1/2 and 14 strains, are very closely related. (iii) all these strains, except for the serotype 1 strain, could harbor a recombinant site for a pathogenic island (89 K) mediated by conjugal transfer, and may have the ability to gain the 89 K sequence.

Conclusions

There is significant genomic diversity among different strains in S. suis, and the gain and loss of large amount of genes are involved in shaping their genomes. This is indicated by (i) pairwise gene content comparisons between every pair of these strains, (ii) the open pan-genome of this species, (iii) the observed indels, invertions and rearrangements in the collinearity analysis. Phylogenetic relationships may be associated with serotype, as serotype 2 strains are closely related and distinct from other serotypes like 1, 3, 7 and 9, but more strains need to be sequenced to confirm this.

Genotypic profile of Streptococcus suis serotype 2 and clinical features of infection in humans, Thailand

To examine associations between clinical features of Streptococcus suis serotype 2 infections in humans in Thailand and genotypic profiles of isolates, we conducted a retrospective study during 2006–2008. Of 165 patients for whom bacterial cultures of blood, cerebrospinal fluid, or both were positive for S. suis serotype 2, the major multilocus sequence types (STs) found were ST1 (62.4%) and ST104 (25.5%); the latter is unique to Thailand. Clinical features were examined for 158 patients. Infections were sporadic; case-fatality rate for adults was 9.5%, primarily in northern Thailand. Disease incidence peaked during the rainy season. Disease was classified as meningitis (58.9%) or nonmeningitis (41.1%, and included sepsis [35.4%] and others [5.7%]). Although ST1 strains were significantly associated with the meningitis category (p<0.0001), ST104 strains were significantly associated with the nonmeningitis category (p<0.0001). The ST1 and ST104 strains are capable of causing sepsis, but only the ST1 strains commonly cause meningitis.

Understanding Streptococcus suis serotype 2 infection in pigs through a transcriptional approach

Background

Streptococcus suis serotype 2 (S. suis 2) is an important pathogen of pigs. S suis 2 infections have high mortality rates and are characterized by meningitis, septicemia and pneumonia. S. suis 2 is also an emerging zoonotic agent and can infect humans that are exposed to pigs or their by-products. To increase our knowledge of the pathogenesis of meningitis, septicemia and pneumonia in pigs caused by S. suis 2, we profiled the response of peripheral blood mononuclear cells (PBMC), brain and lung tissues to infection with S. suis 2 strain SC19 using the Affymetrix Porcine Genome Array.

Results

A total of 3,002 differentially expressed transcripts were identified in the three tissues, including 417 unique genes in brain, 210 in lung and 213 in PBMC. These genes showed differential expression (DE) patterns on analysis by visualization and integrated discovery (DAVID). The DE genes involved in the immune response included genes related to the inflammatory response (CD163), the innate immune response (TLR2, TLR4, MYD88, TIRAP), cell adhesion (CD34, SELE, SELL, SELP, ICAM-1, ICAM-2, VCAM-1), antigen processing and presentation (MHC protein complex) and angiogenesis (VEGF), together with genes encoding cytokines (interleukins). Five selected genes were validated by qRT-PCR analysis.

Conclusions

We studied the response to infection with S. suis 2 strain SC19 by microarray analysis. Our findings confirmed some genes identified in previous studies and discovered numerous additional genes that potentially function in S. suis 2 infections in vivo. This new information will form the foundation of future investigations into the pathogenesis of S. suis.

Slaughterhouse pigs are a major reservoir of Streptococcus suis serotype 2 capable of causing human infection in southern Vietnam

Streptococcus suis is a pathogen of major economic significance to the swine industry and is increasingly recognized as an emerging zoonotic agent in Asia. In Vietnam, S. suis is the leading cause of bacterial meningitis in adult humans. Zoonotic transmission is most frequently associated with serotype 2 strains and occupational exposure to pigs or consumption of infected pork. To gain insight into the role of pigs for human consumption as a reservoir for zoonotic infection in southern Vietnam, we determined the prevalence and diversity of S. suis carriage in healthy slaughterhouse pigs. Nasopharyngeal tonsils were sampled from pigs at slaughterhouses serving six provinces in southern Vietnam and Ho Chi Minh City area from September 2006 to November 2007. Samples were screened by bacterial culture. Isolates of S. suis were serotyped and characterized by multi locus sequence typing (MLST) and pulse field gel electrophoresis (PFGE). Antibiotic susceptibility profiles and associated genetic resistance determinants, and the presence of putative virulence factors were determined. 41% (222/542) of pigs carried S. suis of one or multiple serotypes. 8% (45/542) carried S. suis serotype 2 which was the most common serotype found (45/317 strains, 14%). 80% of serotype 2 strains belonged to the MLST clonal complex 1,which was previously associated with meningitis cases in Vietnam and outbreaks of severe disease in China in 1998 and 2005. These strains clustered with representative strains isolated from patients with meningitis in PFGE analysis, and showed similar antimicrobial resistance and virulence factor profiles. Slaughterhouse pigs are a major reservoir of S. suis serotype 2 capable of causing human infection in southern Vietnam. Strict hygiene at processing facilities, and health education programs addressing food safety and proper handling of pork should be encouraged.

Response of swine spleen to Streptococcus suis infection revealed by transcription analysis

Astract

In vitro characterization of the microglial inflammatory response to Streptococcus suis, an important emerging zoonotic agent of meningitis

Streptococcus suis is an important swine and human pathogen responsible for septicemia and meningitis. In vivo research in mice suggested that in the brain, microglia might be involved in activating the inflammatory response against S. suis. The aim of this study was to better understand the interactions between S. suis and microglia. Murine microglial cells were infected with a virulent wild-type strain of S. suis. Two isogenic mutants deficient at either capsular polysaccharide (CPS) or hemolysin production were also included. CPS contributed to S. suis resistance to phagocytosis and regulated the inflammatory response by hiding proinflammatory components from the bacterial cell wall, while the absence of hemolysin, a potential cytotoxic factor, did not have a major impact on S. suis interactions with microglia. Wild-type S. suis induced enhanced expression of Toll-like receptor 2 by microglial cells, as well as phosphotyrosine, protein kinase C, and different mitogen-activated protein kinase signaling events. However, cells infected with the CPS-deficient mutant showed overall stronger and more sustained phosphorylation profiles. CPS also modulated inducible nitric oxide synthase expression and further nitric oxide production from S. suis-infected microglia. Finally, S. suis-induced NF-κB translocation was faster for cells stimulated with the CPS-deficient mutant, suggesting that bacterial cell wall components are potent inducers of NF-κB. These results contribute to increase the knowledge of mechanisms underlying S. suis inflammation in the brain and will be useful in designing more efficient anti-inflammatory strategies for meningitis.

Streptococcus suis: a new emerging or an old neglected zoonotic pathogen?

Infections caused by Streptococcus suis are considered a global and an economical problem in the swine industry. Moreover, S. suis is an agent of zoonosis that afflicts people in close contact with infected pigs or pork-derived products. Although sporadic cases of S. suis infections in humans (mainly meningitis) have been reported during the last 40 years, a large outbreak due to this pathogen emerged in the summer of 2005 in China. The severity of the infection in humans during the outbreak, such as a shorter incubation time, more rapid disease progression and higher rate of mortality, attracted a lot of attention from the scientific community and the general press. In fact, the number of publications on S. suis (including the number of reported human cases) has significantly increased during recent years. In this article we critically review the present knowledge on S. suis infection in humans, we discuss the hypotheses that may explain the 2005 outbreak and the repercussion of such an episode on the scientific community.

An observational study of the microbiome of the maternal pouch and saliva of the tammar wallaby, Macropus eugenii, and of the gastrointestinal tract of the pouch young

Marsupial mammals, born in an extremely atricial state with no functional immune system, offer a unique opportunity to investigate both the developing microbiome and its relationship to that of the mother and the potential influence of this microbiome upon the development of the immune system. In this study we used a well-established marsupial model animal, Macropus eugenii, the tammar wallaby, to document the microbiome of three related sites: the maternal pouch and saliva, and the gastrointestinal tract (GIT) of the young animal. We used molecular-based methods, targeting the 16S rDNA gene to determine the bacterial diversity at these study sites. In the maternal pouch, 41 unique phylotypes, predominantly belonging to the phylum Actinobacteria, were detected, while in the saliva, 48 unique phylotypes were found that predominantly belonged to the phylum Proteobacteria. The GIT of the pouch young had a complex microbiome of 53 unique phylotypes, even though the pouch young were still permanently attached to the teat and had only been exposed to the external environment for a few minutes immediately after birth while making their way from the birth canal to the maternal pouch. Of these 53 phylotypes, only nine were detected at maternal sites. Overall, the majority of bacteria isolated were novel species (<97 % identity to known 16S rDNA sequences), and each study site (i.e. maternal pouch and saliva, and the GIT of the pouch young) possessed its own unique microbiome.

Clonal dissemination of human isolates of Streptococcus suis serotype 14 in Thailand

Most cases of Streptococcus suis infection in humans are caused by serotype 2 strains, and only a few cases caused by other serotypes have been reported. Among 177 human isolates of S. suis in Thailand, 12 (6.8 %) were identified as being of serotype 14, and an occurrence of sporadic S. suis serotype 14 infection was noted during 2006-2008, particularly in northern Thailand. Clinical presentations of the 12 patients (median age 62.9 years) included meningitis (58.3 %), septic arthritis (25 %) and sepsis (16.7 %). These clinical features were similar to those previously reported for S. suis infections, except that there were no fatal cases. All of the 12 serotype 14 strains belonged to the multilocus sequence types (ST) 105 (n=11) and the novel ST127 (n=1). Molecular typing by PFGE revealed four different pulsotypes, including an identical pattern for nine ST105 strains and three closely related patterns for two ST105 strains and one ST127 strain. Our PFGE data suggested clonal dissemination of ST105 strains in Thailand. Because serotype 14 is becoming a more common cause of S. suis infections in humans, diagnostic tests for serotype 14 should be performed in South-East Asian countries.