Streptococcus suis : an important zoonotic pathogen for human – prevention aspects

Streptococcus suis is a major porcine pathogen, causing economical health worldwide problems in the global swine industry. It is also emerging as a zoonotic agent capable of causing severe invasive disease in humans exposed to pigs or pork products. The most important clinical sign in swine and human is meningitis, but other pathological conditions have also been described. Serotype 2 is the most commonly associated with diseases in pigs and humans, and also the most frequently reported serotype isolated from diseased animals worldwide. The majority of human infection occurs in pork handlers, particularly in slaughterhouse workers and by minor wounds or skin abrasions contaminated by raw pork or viscera of pigs. Veterinarians should also be aware that a low but real risk may be present when manipulating S. suis-diseased animals that are probably shedding high numbers of this pathogen. Up today, in Greece there is no published epidemiological data for S. suis serotypes in swine herds and the zoonotic risk of S. suis infection in human with daily contact with pigs and pork meat. However, in our experience clinical forms of S. suis infection are common in most greek swine farms. The aim of this review study is to perform recent information about S. suis infection in swine and human, focus on zoonotic risk of this emerging pathogen and prevention strategies.


Introduction
Various bacterial components such as extracellular and cell membrane-associated proteins have Streptococcus suis (S. suis) is a major porcine been suggested as virulence-associated factors, but pathogen endemic in all countries with a developed their precise roles in the pathogenesis or virulence of S. swine industry, causing great economic loss every suis have not been established (Gottschalk et al 1999, year.Although S. suis is considered primarily a swine Gottschalk and Segura 2000).Serotype 2 of S. suis pathogen, it has been increasingly isolated from a wide (SS2) is the most commonly associated with diseases range of animal species eg, cattle, sheep, goats, horses, in pigs and humans, and also the most frequently including human beings, and birds, which suggests reported serotype isolated from diseased animals new concepts about some epidemiological aspects of worldwide (Wisselink et al. 2000, Hill et al. 2005, the infection.Silva et al., 2006, Higgins andGottschalk 1999).SS2 S. suis is s an α-hemolytic streptococci related to is the most prevalent type in clinical material from pigs Lancefield group, a gram-positive, encapsulated in Europe (Wisselink et al. 2000) and the infection bacterium causes many different swine diseases.35 causes severe disease outbreaks in swine herds.different serotypes of S. suis have been described, The epidemiology of S. suis occurrence among along with subtypes defined as different genotypes pigs is complex; it usually occurs as normal flora, but within these serotypes (King et al. 2001).S. suis may be infectious or even lethal, especially among comprises of pathogenic, weakly pathogenic, and weaning piglets.Most clinically healthy pigs are nonpathogenic strains (Gottschalk et al. 1999 (Mai et al. 2008).Although human the piglet during parturition (Amass et al. 1996) and infection with S. suis has been occasionally colonizes the tonsil soon after birth (Amass et al. documented in North America (Gottschalk et al. 1995).Transmission between herds occurs usually by 2004), the first human case was not reported in the the movement of healthy carrier pigs.Their United States until 2006 (Willenburg et al. 2006).In introduction into a non infected herd usually results in Greece, the first case of S. suis septicemia and the subsequent onset of disease in weaners and/or meningitis reported in 2005 (Mazokopakis et al. growing pigs.However, some infected herds that 2005).It was a case of septicemia caused by S22 show no illness may develop clinical disease in the complicated by meningitis and deafness in an elderly presence of other predisposing factors, such as Porcine woman with history of prior contact with unprocessed Reproductive and Respiratory Syndrome Virus pork meat.The causative agent was isolated from both (PRRSV).S. suis can also be transmitted via fomites the blood cultures and the cerebrospinal fluid.The and flies.The importance of other animal species or patient's condition improved after treatment with birds as reservoirs or vectors of the infection is unknown.
penicillin, but deafness became permanent.Although, the most important clinical manifestation Occasionally it affects humans, particularly in swine is meningitis, other pathological conditions those occupationally exposed to pigs or pig products, have also been described, such as meningitis, causing meningitis, septicemia, endocarditis, toxic endocarditis, septicemia with sudden death, arthritis shock syndrome, arthritis, acute deafness, or other and pneumonia, abortions, and abscesses (Gogolewski illnesses (Tarradas et al. 2001).Analysis of SS2 serotypes, followed by serotypes 3 (14.7%)and 4, 8, 5, strains recovered from tonsils of healthy pigs from 7, 1/2 (3.2-6.4%).SS2 was more frequently isolated those farms were genotypically similar (but not from swine with systemic infection, while serotype 3 identical) to the human strains.The slight differences was significantly associated with pneumonia.
between isolates were probably the consequence of adaptation to the new host or simply lack of People in daily contact with pigs (such as pig reproducibility of the detection technique.Virulence farmers, abattoir workers, persons transporting pork, properties of strains isolated from pigs or humans meat inspectors, and butchers) are usually affected seem to be similar (Gottschalk and Segura 2000).through the skin via a cut, infected wound or abrasion (Robertson and

Hendriksen et al. 2008). Adjunctive therapy with an
The incubation period ranges from a few hours to 2 anti-inflammatory agent is also recommended for days (Lütticken et al. 1986).Manifestation of disease treatment of S. suis meningitis in pigs.Animals with in pigs is not a prerequisite for infections in people in advance septicemia, meningitis and arthritis rarely contact with pigs, since most animals are colonized by S. suis respond and all cases should be re-assessed 3 days without clinical signs (Higgins and Gottschalk after the onset of treatment.Pigs in the same pen as 1999).In addition to domestic pigs, wild boars may S. suis affected animals should be treated in feed or in water.also be a source of infection for hunters and Control of the disease in older pigs can be by poachers (Halaby et al. 2000).From studies of medication of the water with ampicillin or amoxicillin contamination of hands and knives, it was concluded with phenoxymethyl penicillin or procaine penicillin that eviscerators involved in removing the larynx and at 75-100g/tn at 200-300g/tn in feed for 7 days prior to lungs from the carcasses have a significantly higher S. suis expected disease.Penicillins should be orally risk of exposure to than other abattoir workers administered through drinking water to reduce the (Breton et al 1986).Finally, one documented case in a interference in absorption due to feed.Amoxicillin has veterinary surgeon has been reported (Walsh et al. advantages over natural penicillins for mass 1992).In very few cases, there was no apparent medication-its body clearance is lower than that of connection with exposure to pigs or pork products penicillin V, and higher serum concentrations are (Strangmann et al. 2002).In addition, splenectomy, obtained (Higgins and Gottschalk 1999).and to a lesser extent, alcoholism, have been suggested Control of the disease in piglets may be possible as important predisposing factors for development of S. suis by farrowing sows in isolation and by fumigating the serious disease (Watkins et al. 2001, Gallagher 2001).accommodation between animals.Injection of piglets In general, S. suis isolates from humans are at birth with long-acting penicillin may prevent phenotypically and genotypically similar to those disease.All-in, all-out husbandry methods can reduce the spread of infection.Medicated early weaning has recovered from pigs.In 2001, two cases of meningitis eradicated disease from a herd but slaughter, in a butcher and an abattoir worker who handled pork disinfection and repopulation is most reliable (Higgins meat that originated from the same three closed farms and Gottschalk 1999).Up today commercial or suggested that the appropriate handling of fresh pork products can prevent the infection and early diagnosis autogenous bacterins vaccines have been used, but with early treatment may prevent disabling deafness.their efficacy is under discussion (Wisselink et al 2000, Baums et al 2009).
Generally, people with close contact to pigs or Prevention of Human infection: While workers unprocessed pork have to observe rules of personal handling fresh pork products in slaughterhouse need and environmental hygiene, which include: awareness, more evidences from recent reports showavoiding generating skin lesions during meat that pig breeder, butchers and any persons who handle processing procedures should be taken or eat uncooked pork products can be at high risk ofcovering open wounds with water-proof infection by S. suis (Martin et , carriers of multiple serotypes of S. suis The natural Gottschalk and Segura 2000, Smith et al. 2001, King et habitat of S. suis is the upper respiratory tract (particularly the tonsils and nasal cavities) (Gottschalk al. 2001).and Segura 2000), and the genital and alimentary 1993, BOE 2005, Rusmeechan and Sribusara 2008), in tracts of pigs (Higgins and Gottschalk 1999).S. suis is Hong Kong (Hui et al. 2005), in China (Ye et al. 2006) transferred from vaginal secretions to the oral cavity of and Vietnam which are commonly fulminant and often et al. 1990, Higgins and Gottschalk 1999, King et al. fatal (Arends et al 1988, Bungener et al 1989, Shneerson et al 1980).Outbreaks accompanied by sudden death, dyspnea, cyanosis, and of SS 2 in humans were reported in People's Republic wasting.Septicemia, arthritis, and bronchopneumonia/ of China in 1998 and 2005 (WHO 2005).In these Pneumonia are less common signs and rhinitis, outbreaks 215 humans were infected and 38 of them abortions, and vaginitis may also occur (Touil et al. died, mainly by streptococcal toxic shock syndrome 1988, Sanford and Higgins 1992, Higgins and (STSS) and some of them by meningitis or severe Gottschalk 1999, Huang et al. 2005).septicemia (Hu et al. 2000, Yu et al. 2006).This Peetermans et al 1989, Trottier et al 1991, Staats et al 2001, Smith et al. 2001, Huang et al. 2005, Gottschalk 1997, Ruoff et al 2003, Lun 2007, Wertheim et al et al. 2007).Clinical infections are seen mainly in 2009).A carriage state has been documented in pigs, weaning or growing pigs and less frequently in healthy carriers being a source of S. suis transmission suckling piglets.The earliest sign is usually fever, in herds, mainly through the respiratory route which may occur initially without other obvious signs.(Gottschalk et al 2007).As discussed in recent reports, Blackmore 1989, Tarradas et al.Aarestrup et al. 1990, Escudero et al. 2007, (Strangmann et al. 2002, Sala and Colombo 1989).
al 2001, (Donsakul et al dressing 2003).The S. suis meningitis usually responds verywashing hands, arms and other exposed parts well to treatment with large doses of intravenous of the body through after each contact with penicillin.Rarely the organism is resistant to pigs or pork meat penicillin.Nevertheless within 24 hours of treatment, -keeping the uncooked pork apart from other the fever, and the headache and the neck stiffness often cooked food o resolve, and deafness is usually permanent.-cooking pork to an temperature of 70 C or until Several investigators have suggested that the the juice is clear and not pink infrequent diagnosis of human S. suis infection is dueconsulting a doctor in case of febrile illness after to under diagnosis or misdiagnosis, rather than a true exposure to pigs or pork meat.absence of disease (Gottschalk et al 2004, Donsakul et