Streptococcosis occurs in pig farms, and it is more likely that pig farmers do not pay attention to these small details.

I. introduction of pig disease

Streptococcus suis is a zoonotic disease caused by a variety of pathogenic streptococcal infections, including porcine lymph node abscess and porcine hemorrhagic streptococcosis. Septicemia, suppurative lymphadenitis, meningitis and arthritis are the main features of the disease. Streptococcus suis type 2 can cause meningitis, septicemia and endocarditis in humans and, in severe cases, death. Streptococcus suis disease occurs in all countries with developed pig industry. With the development of large-scale pig industry in China, Streptococcus suis has become a common and frequently-occurring disease in pig production.

II. Epidemiology

Streptococcus is a conditional pathogen with many species and is widely distributed in nature and pig herds.

Often found in healthy mammals and humans. Pigs were susceptible to pigs regardless of age, breed and sex, but most of them broke out in piglets aged from 3 weeks to 12 weeks, especially in weaning and mixed herds.

Its mode of transmission is mainly through mouth or respiratory tract, but it can also be transmitted vertically (some newborn piglets can be infected during delivery). Streptococcus suis colonized in the upper respiratory tract (especially nasal cavity and tonsil), reproductive tract and digestive tract of pigs. The carrying rate of porcine tonsils aged 4 weeks to 6 months was 32% and 50%.

Diseased pigs and dead pigs are the main sources of infection. Subclinical healthy pigs with bacteria can expel bacteria to become the source of infection, which plays an important role in the infection of young pigs. The ratio of pigs carrying the pathogen is between 0% and 100%. However, there is no significant correlation between the carrying rate of the pathogen and the incidence of the disease.

The epidemic of Streptococcus suis has no obvious seasonality and can occur in all seasons of the year, but it is easy to occur in a large area from July to October. Streptococcus suis infection in humans has no obvious seasonality, and the outbreak of the disease is regional. Streptococcosis can be induced when stress factors such as mixed herd, immune inoculation, high temperature and humidity, climate change and poor sanitary conditions of enclosure are introduced from other places to reduce the resistance of animals. Insect vectors play an important role in the spread of disease, transmitting pathogens through flight between pig farms. Among the many serotypes of Streptococcus suis, type 2 is the main pathogen of pigs and has the strongest pathogenicity. Of all Streptococcus suis isolated from healthy porcine tonsils, type 2 is as high as 50.6%, and it is also the most pathogenic to humans.

III. Clinical symptoms

In clinical treatment, Streptococcus suis is mainly characterized by septicemia, meningitis, arthritis and lymph node abscess. It can be divided into the following types:

1. Septic type

It is mainly common in the most acute cases at the beginning of the epidemic, the onset is acute, the course of disease is short, and pigs often die suddenly without any abnormal symptoms. Or suddenly reduce or stop eating, mental fatigue, body temperature rising to 41-42 ℃, dyspnea, constipation, conjunctival cyanosis, lying on the floor, reddish foam-like fluid from mouth and nose, and most of them died within 6-24 hours.

The acute cases of sick pigs showed mental depression, body temperature up to 43 ℃, missed fever, loss of appetite, eye conjunctival flush, tears, serous nasal juice, shortness of breath, cough, purplish red skin in neck, auricle, abdomen and lower extremities, bleeding spots, lameness, longer course of disease, and died within 3 to 5 days. The morbidity is generally about 30%, and the mortality rate can reach 80%.

two。 Meningitis type

Most of them occur in suckling piglets and weaned piglets, the initial body temperature rises to 40.5-42.5 ℃, stop eating, constipation, serous and sticky nose, neurological symptoms, such as motor disorders, blind walking, turning, empty chewing, molars, supine, hindquarters paralysis, lying on the ground, limbs moving, like swimming. Most of the acute type died at 30 to 36 hours.

The course of subacute or chronic disease is slightly longer, mainly manifested as polyarthritis, gradual wasting, exhaustion, death, or recovery.

3. Arthritis type

Mainly transferred from the first two types, or manifested as arthritis from the onset of the disease. The diseased pig was unable to stand because of swelling, pain and lameness in one limb or several pancreatic joints. The course of disease was 2-3 weeks.

4. Lymph node abscess type

This type is caused by Streptococcus suis infection through mouth, nose and skin. Weaning piglets and fattening pigs are common, with slow transmission and low incidence, but once the pig herd occurs, it is difficult to remove.

The main manifestations are suppuration and abscess of lymph nodes in submandible, pharynx, neck and so on. The affected lymph nodes initially appeared a small abscess, and then gradually enlarged. 3 weeks after infection, the local area was significantly raised, and the palpation was hard and had thermal pain. The feeding, chewing, swallowing and breathing of diseased pigs are all impaired. After the abscess matures, the epidermis is necrotic, ruptures and flows out of pus. After the discharge of pus, the systemic symptoms were significantly alleviated, and the granulation tissue grew and scarred and healed. The course of disease ranged from 3 to 5 weeks.

IV. Pathological changes

1. Acute septic type

Poor blood coagulation, purple spots on the skin, subcutaneous hemorrhage of mucous membrane and serosa. Purplish red nasal mucosa, hyperemia and bleeding. The throat and trachea are congested and a lot of foam is common. Lungs are congested and swollen. The lymphatic vessels of the whole body have different swelling, congestion and bleeding. Pericardial effusion, yellowish, a few mild fibrinous pericarditis, endocardial bleeding. Mild fibrinous pleurisy can be seen in some cases. There is a small amount of yellowish effusion in the abdominal cavity and some of them have mild fibrinous peritonitis. In most cases, splenomegaly was enlarged, and a few cases were enlarged by 1 Mel 3 times, showing dark red or purplish blue, soft and brittle. There are varying degrees of congestion and bleeding in the mucosa of stomach and small intestine. The kidneys are mildly enlarged, congested and bleeding. The meninges have varying degrees of congestion, sometimes bleeding.

two。 Meningitis type

Meningeal congestion, hemorrhage, severe hemorrhage, a few submeningeal effusion, obvious dot hemorrhage in white matter and gray matter, and other changes similar to septic type.

3. Chronic type

In endocarditis, the heart valve thickens, the surface is rough, and there are cauliflower-like vegetation on the valve, commonly seen in the bicuspid or tricuspid valve, and sometimes in the atria, ventricles and blood vessels. When arthritis, there are yellow jelly-like fluid or cellulosic purulent substance inside and outside the joint capsule.

5. Diagnosis and differentiation

According to the epidemic characteristics, symptoms and pathological changes of the disease, only a preliminary diagnosis can be made, and the diagnosis depends on laboratory diagnosis.

1. Microscopic examination of smears is a relatively simple diagnostic method. Liver, spleen, lymph node, blood, synovial fluid, pus and other diseased materials of diseased pigs can be smeared for microscopic examination to observe whether there are typical streptococci or not.

two。 Isolation and culture of bacteria. Aseptic materials such as liver, spleen, lymph nodes, blood, synovial fluid and pus were inoculated on blood Agar plate to observe colony growth, hemolysis and hemolysis types. If there is β-type hemolysis in the colony, the bacterial morphology and biochemical identification are further done. Further serological and typing identification can be done. The virulence factors of the strains were identified by PCR.

3. Animal inoculation test. The diseased materials or bacterial cultures were inoculated into rabbits, mice and pigeons to observe the incidence of experimental animals, recover and identify bacteria from dead animals.

The differential diagnosis of the disease should be different from listeriosis, porcine erysipelas, porcine paratyphoid and classical swine fever.

VI. Comprehensive prevention and control

1. Treatment information

The diseased pigs were isolated and treated according to different disease types. For lymph node abscess, cut open in time when the abscess matures (soften), remove pus, rinse with 30% hydrogen peroxide or 0.1% potassium permanganate, and apply iodine tincture.

Large doses of antibiotics or sulfonamides should be used in the early stage for septicemia or meningitis. 40-1 million units of penicillin were injected intramuscularly 4 times a day, and gentamicin 1 Mel 2 mg / kg body weight, twice a day. It can also be treated with acetylciprofloxacin, 2.5ml 10mg / kg body weight, injected every 12 hours for 3 days, can quickly improve the symptoms, the curative effect is significantly better than penicillin.

two。 Prevention information

(1) isolate diseased pigs and eliminate the source of infection. The carcass of suspected diseased pigs was found after slaughtering and could only be eaten after high temperature treatment. Remove sharp objects from the pigsty.

(2) the immune prevention epidemic area (field) was first immunized with aluminum hydroxide vaccine of Streptococcus suis at the age of 60 days, and then it was immunized once a year in spring and autumn, regardless of whether the pigs were injected intramuscularly or subcutaneously, and the concentrated vaccine was injected with 3 milliliters. Immunity was produced 21 days after injection, and the immune period was about 6 months. The attenuated vaccine of Streptococcus suis was injected intramuscularly or subcutaneously with 1 ml per pig for 14 days to produce immunity for six months.

(3) after the occurrence of the disease in the drug prevention pig farm, if the vaccine is not available temporarily, drug prevention can be used to prevent the occurrence of the disease. 125g tetracycline was added to each ton of feed and fed with 4Mel for 6 weeks.

3. Public Health

(1) strengthening pig quarantine where diseased pigs detected before slaughter should be urgently isolated and slaughtered two weeks after recovery, and those who find suspicious diseases after slaughter should be treated innocuously. Emergency slaughtering pigs should be treated in a separate emergency slaughtering room to prevent pollution of healthy pork. All pigs that are urgently slaughtered are not allowed to be sold without harmless treatment. The slaughterhouse swill must be boiled before it can be fed. At the same time, strengthen the disinfection and hygiene system of slaughterhouses and pig trading markets.

(2) Human beings should stay away from diseased animals, do not eat diseased pork and diseased pork without harmless treatment, do not come into direct contact with sick and dead animals, and pay attention to the disinfection of castration, injection and delivery of umbilical cord.

(3) once the disease breaks out and spreads, according to the Animal epidemic Prevention Law, emergency isolation, blockade and measures should be taken immediately to control and exterminate animal diseases in time.