Prevention and treatment of Streptococcus suis

Streptococcus suis is a zoonotic disease caused by a variety of pathogenic Streptococcus suis infection. Among them, pig is the main source of infection. The disease is not common in humans, but it is generally susceptible, mainly characterized by fever and severe toxic blood symptoms. After early diagnosis and timely treatment, most patients can be cured, but some patients will leave sequelae.

Harm of Streptococcus suis disease

Streptococcus suis has a high prevalence in pigs, but it is not common in humans, but the disease is very serious. The population is generally susceptible, especially butchers, abattoir workers and farmers. Other people such as people who transport and clean up sick / dead pigs, such as drivers, are also susceptible to Streptococcus suis. Workers in slaughterhouses can carry bacteria in their pharynx, and they may be in a state of health, but they are potentially dangerous. The disease first broke out in pigs, followed by butchers and those related to the treatment of disease and dead pigs, especially in modern intensive pig farming. The time of onset is relatively concentrated in the high temperature season from June to August. Human cases of Streptococcus suis infection were reported as early as 1968 in the Netherlands and Denmark, and then cases were reported in Sweden, France, Britain, Belgium, Italy, Germany, New Zealand, Canada and China. At present, more than 450 cases of Streptococcus suis infection have been reported worldwide, mainly in some countries and regions where pork is raised and eaten in Northern Europe and South Asia. In 1998, there were 25 cases of Streptococcus suis epidemic in Nantong, Jiangsu Province, including 16 cases of toxic shock syndrome (13 deaths) and 9 cases of meningitis (1 death). According to the Ministry of Health, from June to August 2005, a total of 204 cases of Streptococcus suis infection were reported in Sichuan Province, of which 38 died and 166 were cured and discharged from hospital. The cases were distributed in 12 cities, 37 counties, 131 townships and 195 villages in Ziyang, Neijiang and Chengdu. In fact, in the vast rural areas, there are sporadic cases every year, because the level of diagnosis is not enough, or can not identify pathogens, untimely treatment of death cases occur from time to time.

Causes of Streptococcus suis disease

Pigs are the main source of infection, especially sick pigs and infected pigs are the main sources of infection, followed by sheep, horses, deer, birds, poultry (such as ducks, chickens) and so on. The carrying rate of Streptococcus suis in pigs is about 20% and 40%, which does not cause disease under normal circumstances. If the bacteria produce virulence variation, causing disease in pigs, the bacteria and toxins in dead pigs are then transmitted to humans, causing disease in humans. So far, no human as a source of infection has been found to cause human disease.

The natural infection sites of Streptococcus suis are upper respiratory tract (especially tonsil and nasal cavity), reproductive tract and digestive tract of pigs. It is mainly transmitted through open wounds, such as human skin or mucous membrane wounds contact with the blood and body fluids of dead pigs, so the incidence of butchers and slaughterhouse workers is relatively high. In some patients, the disease is caused by eating unclean salad / dead pork or raw pork balls, washing and cutting diseased / dead pork, and the processing of frozen pork can also cause sporadic cases. Some patients can also be transmitted through the respiratory tract. It is transmitted from pig to pig through respiratory tract and close contact, but there is no evidence to suggest human transmission through pig respiratory tract.

Pathogenesis of Streptococcus suis disease

At present, the mechanism of human streptococcosis has not been fully elucidated, and there are few studies on the pathogenesis of human Streptococcus suis infection.

The occurrence of porcine streptococcosis is related to the immune status of pigs, environmental factors and the virulence of pathogenic strains. Streptococcus suis, which causes meningitis, septicemia and arthritis syndrome, needs virulence factors that increase bacterial invasiveness, including capsular polysaccharides (CPS), lysozyme release protein (MRP), extracellular factors (EF) and hemolysin (SLY). Streptococcus suis type 2 non-capsular mutant and unknown serotype (NT) Streptococcus suis showed strong adhesion and invasiveness. Studies have shown that Streptococcus suis type 2 can induce human monocytes to produce tumor necrosis factor α (TNF α), IL-1, IL-6, IL-8 and monocyte chemoattractant protein l (MCP-1). These cytokines can cause systemic inflammatory response. The capsular lipopolysaccharide of Streptococcus suis type 2 is related to the adhesion and invasion of bacteria, and the strains with capsule can resist phagocytosis, so the capsular lipopolysaccharide plays an important role in the pathogenic mechanism, resulting in the decrease of phagocytosis of Streptococcus suis.

When bacteria enter the blood from the tonsil and are swallowed by monocytes, they enter the cerebrospinal fluid through the choroid plexus and stimulate monocytes or macrophages to produce cytokines and toxins, resulting in inflammatory cell infiltration in the blood and cerebrospinal fluid. The pathogenesis of Streptococcus suis pneumonia may be due to the colonization and reproduction of a large number of bacteria through the respiratory tract, producing toxins and various proteases, hemolytic toxins, etc., resulting in the destruction of epithelial cell barrier and pulmonary infection. at the same time, it is beneficial for pathogens to invade the bloodstream and spread throughout the body. In addition, cytokines and toxins increase the permeability of blood-brain barrier (BBB) in patients with bacterial meningitis, lead to brain edema, increase intracranial pressure and block cerebral blood flow. After Streptococcus suis infection directly from the wound, bacteria multiply in large numbers in the body, producing toxins, resulting in hematogenous infection, resulting in septicemia and multiple organ failure, which is similar to septicemia caused by common bacteria.

The pathological changes mainly involved many organs of the whole body. Congestion or bleeding often occurs in the organs of the whole body during septicemia. Congestion of meninges, lymph nodes and lungs can be seen in some pigs with meningitis. The most typical histopathological features of meningitis are diffuse infiltration of neutrophils, fibrin exudation, edema and inflammatory cell infiltration in meninges and choroid plexus. The lungs often show substantial lesions, including fibrin hemorrhagic and interstitial fibrinous pneumonia, fibrinous or suppurative bronchopneumonia, alveolar hemorrhage, interlobular emphysema, and fibrous suppurative pleurisy. Cardiac lesions include fibrinogenic suppurative pericarditis, mechanical valvular endocarditis and hemorrhagic myocarditis. The histopathological changes were dotted or patchy diffuse hemorrhage or necrosis of myocardium and suppurative liquefaction of fibrin. Pericardial fluid often contains eosinophils, a small number of neutrophils, monocytes and a large amount of fibrin.

The above is the pathogenesis of Streptococcus suis infection in pigs, whether the process of occurrence and development of human Streptococcus suis infection is the same as that of pigs, or there is any difference, there is little or lack of research.