How to carry out emergency prevention and control of swine streptococcosis? Interpretation of the technical specification

Swine streptococcosis is a zoonotic disease caused by hemolytic Streptococcus, and it is a Class II animal disease as stipulated in China.
To guide the prevention and control of swine streptococcosis in all regions and protect the development of the livestock industry and human health and safety, this specification is formulated in accordance with the relevant provisions of the Animal Epidemic Prevention Law of the People's Republic of China and the National Emergency Plan for Major Sudden Animal Epidemics.
1 Scope of application
This specification stipulates the diagnosis, epidemic reporting, epidemic handling, and prevention and control measures for swine streptococcosis.
This specification applies to all units and individuals within the territory of the People's Republic of China engaged in pig raising, slaughtering, transportation, and the processing, storage, sales, and transportation of pig products, as well as those engaged in animal epidemic prevention activities.
2 Diagnosis
Diagnosis is made based on epidemiological characteristics, clinical symptoms, pathological changes, and laboratory tests.
2.1 Epidemiological characteristics
Pigs, equine animals, cattle, sheep, goats, chickens, rabbits, mink, and some aquatic animals are all susceptible. Pigs of different ages, breeds, and sexes are all susceptible.
Streptococcus suis can also infect humans.
In addition to being widely present in nature, this bacterium often exists in the respiratory tract, digestive tract, and reproductive tract of normal animals and humans. The pathogen is present in the excretions, secretions, blood, internal organs, and joints of infected animals.
Sick pigs and carrier pigs are the main sources of infection for this disease. Improper disposal of dead pigs and contamination of transport vehicles are important factors in the spread of this disease.
This disease is mainly transmitted through the digestive tract, respiratory tract, and damaged skin.
This disease can occur throughout the year, but is more common in summer and autumn. It occurs as an endemic disease; in new epidemic areas it may occur as an outbreak with higher morbidity and mortality. In old epidemic areas it mostly occurs sporadically, with lower morbidity and mortality.
2.2 Clinical symptoms
2.2.1 This specification stipulates that the incubation period of this disease is 7 days.
2.2.2 It may present as septicemic, meningitis, and lymph node abscess types, among others.
2.2.2.1 Septicemic type: divided into three categories: peracute, acute, and chronic.
The peracute type has a sudden onset and short course, often with sudden death without any symptoms. Body temperature reaches as high as 41-43°C, breathing is labored, and most die of septicemia within 24 hours.
The acute type mostly occurs suddenly, with body temperature rising to 40-43°C, showing continuous fever. Breathing is labored, the nasal mirror is dry, and serous or purulent secretions flow from the nasal cavity. The conjunctiva is congested and there is tearing. The skin of the neck, ear margins, underbelly, and lower parts of the limbs is purplish red with hemorrhagic spots. Most die within 1-3 days.
The chronic type presents as multiple arthritis. Joints swell, with lameness or paralysis, and finally death from weakness and paralysis.
2.2.2.2 Meningitis type: mainly meningitis, mostly seen in piglets. The main manifestations are neurological symptoms, such as teeth grinding, foaming at the mouth, circling movement, convulsions, lying down with limbs paddling as if swimming, and finally death from paralysis. The course may be as short as a few hours or as long as 1-5 days, with an extremely high fatality rate.
2.2.2.3 Lymph node abscess type: characterized by suppuration and abscess formation in the lymph nodes of the submandibular, pharyngeal, and cervical regions.
2.3 Pathological changes
2.3.1 Septicemic type: necropsy shows purplish red nasal mucosa, congestion and hemorrhage, congestion of the larynx and trachea, often with large amounts of foam. The lungs are congested and swollen. Systemic lymph nodes show varying degrees of enlargement, congestion, and hemorrhage. The spleen is enlarged 1-3 times, dark red, with black-red hemorrhagic infarct areas at the edges. The gastric and small intestinal mucosa show varying degrees of congestion and hemorrhage, the kidneys are enlarged, congested, and hemorrhagic, the meninges are congested and hemorrhagic, and in some cases pinpoint-sized hemorrhagic spots can be seen on the brain cut surface.
2.3.2 Meningitis type: necropsy shows congestion, hemorrhage, or even bleeding of the meninges, with subdural effusion in a few cases, pinpoint hemorrhage on the brain tissue cut surface, and other lesions the same as the septicemic type.
2.3.3 Lymph node abscess type: necropsy shows yellow gelatinous or fibrinous, purulent exudate in the joint cavity, and lymph node abscesses. In some cases there are cauliflower-like vegetations on the heart valves.
2.4 Laboratory tests
2.4.1 Smear microscopy: tissue impression smears or blood smears show Gram-positive spherical or oval bacteria, without spores, some of which may form capsules, often appearing as single or paired bacteria, occasionally in short chains.
2.4.2 Isolation and culture: this bacterium is aerobic or facultatively anaerobic. When inoculated on blood agar plates and cultured at 37°C for 24 hours, it forms colorless, dewdrop-like small colonies, with hemolysis around the colonies. Microscopy shows bacteria arranged in chains of varying lengths.
2.4.3 When necessary, PCR methods are used for bacterial type identification.
2.5 Interpretation of results
2.5.1 Any one of the following conditions is judged as suspected swine streptococcosis
2.5.1.1 Meets one of the clinical symptoms in 2.2.2.1, 2.2.2.2, or 2.2.2.3.
2.5.1.2 Meets one of the necropsy lesions in 2.3.1, 2.3.2, or 2.3.3.
2.5.2 Confirmed diagnosis
Meets one of 2.5.1.1 or 2.5.1.2, and also meets one of 2.4.1, 2.4.2, or 2.4.3.
3 Epidemic reporting
3.1 Any unit or individual that discovers pigs suffering from or suspected of this disease shall promptly report it to the local animal epidemic prevention supervision institution.
3.2 After receiving an epidemic report, the local animal epidemic prevention supervision institution shall report it upward in accordance with the relevant provisions on national animal epidemic reporting management.
3.3 After the epidemic is confirmed, the animal epidemic prevention supervision institution shall promptly report it to the veterinary administrative department at the same level, and the veterinary administrative department shall notify the health department at the same level.
4 Epidemic handling
The diagnosis made based on epidemiology, clinical symptoms, and necropsy lesions, combined with laboratory tests, can serve as the basis for epidemic handling.
4.1 When a suspected swine streptococcosis epidemic is discovered, the local animal epidemic prevention supervision institution shall promptly send personnel to the site to conduct epidemiological investigation, clinical symptom examination, etc., and collect samples for testing. When it is confirmed as a suspected swine streptococcosis epidemic, isolation, movement restriction, and other prevention and control measures shall be taken immediately.
4.2 When a swine streptococcosis epidemic is confirmed, handle it according to the following requirements
4.2.1 Delineation of the epidemic point, epidemic area, and threatened area
The veterinary administrative department at or above the county level in the locality shall delineate the epidemic point, epidemic area, and threatened area.
Epidemic point: refers to the location of the sick pigs. Generally it refers to the farm (household group) or other relevant slaughtering or operating unit where the sick pigs and animals in the same group are located.
Epidemic area: refers to the area within a radius of 1 km centered on the epidemic point. When actually delineating the epidemic area, local raising environment and natural barriers (such as rivers, mountains, etc.) as well as meteorological factors should be considered to scientifically determine the scope of the epidemic area.
Threatened area: refers to the area extending 3 km outside the epidemic area.
4.2.2 When this disease occurs sporadically, sick pigs shall be killed without bloodletting, and pigs in the same group shall immediately receive compulsory immunization or drug prophylaxis and be isolated and observed for 14 days. When necessary, pigs in the same group shall be killed. Killed pigs, dead pigs, and their excretions, possibly contaminated feed, sewage, etc. shall be harmlessly treated in accordance with relevant provisions; possibly contaminated articles, vehicles, utensils, and livestock houses shall be strictly and thoroughly disinfected. All susceptible animals in the epidemic area and threatened area shall receive emergency immunization.
4.2.3 When this disease occurs as an outbreak (more than 50 sick pigs found within 30 days in one township, or occurrence in more than 2 townships), the provincial animal epidemic prevention supervision institution shall use PCR methods for bacterial type identification, and at the same time request the county-level people's government to impose a blockade on the epidemic area; after receiving the blockade report, the county-level people's government shall issue a blockade order within 24 hours and implement the blockade on the epidemic area. The handling measures taken for the epidemic point, epidemic area, and threatened area are as follows:
4.2.3.1 Epidemic point: disinfection facilities must be set up at entrances and exits. Entry and exit of people, animals, and vehicles and the transport out of animal products and possibly contaminated articles shall be restricted. Livestock houses, sites, and all transport vehicles, drinking water utensils, etc. within the epidemic point must be strictly and thoroughly disinfected.
Sick pigs shall be killed without bloodletting, and pigs in the same group shall immediately receive compulsory immunization or drug prophylaxis and be isolated and observed for 14 days. When necessary, pigs in the same group shall be killed. Dead pigs and their excretions, possibly contaminated feed, sewage, etc. shall be harmlessly treated in accordance with the requirements of the annex; possibly contaminated articles, vehicles, utensils, and livestock houses shall be strictly and thoroughly disinfected.
4.2.3.2 Epidemic area: animal epidemic prevention supervision and inspection stations shall be established at key traffic routes, with dedicated personnel supervising the movement of animals and their products, and people and vehicles entering and exiting must be disinfected. Trading, slaughtering, transportation, and movement of live pigs in the epidemic area shall be stopped. Livestock houses, roads, and other possibly contaminated places shall be disinfected.
All susceptible animals in the epidemic area shall receive emergency immunization.
4.2.3.3 Threatened area: all susceptible animals in the threatened area shall receive emergency immunization.
Pig houses, sites, and all transport vehicles, drinking water utensils, etc. shall be strictly and thoroughly disinfected.
4.2.4 Harmless treatment
All dead pigs, killed pigs, and possibly contaminated products (including pork, internal organs, bones, blood, skin, hair, etc.) shall be handled in accordance with GB 16548 "Protocol for Harmless Treatment of Diseased Livestock and Poultry Carcasses and Their Products"; pig excretions and contaminated or possibly contaminated bedding, feed, and other items all need harmless treatment.
When pig carcasses need to be transported, leak-proof containers shall be used, and this shall be carried out under the supervision of the animal epidemic prevention supervision institution.
4.2.5 Emergency prevention
4.2.5.1 For healthy pigs in the same group within the epidemic point and pigs within the epidemic area, highly sensitive antibacterial drugs may be used for emergency preventive administration.
4.2.5.2 All pigs in the epidemic area and threatened area shall receive emergency immunization according to the instructions, and immunization records shall be established.
4.2.6 Conduct source analysis and epidemiological investigation.
4.2.7 Lifting of the blockade order
After all pigs and their products within the epidemic point have been handled according to provisions, the relevant sites and articles shall be thoroughly disinfected under the supervision and guidance of the animal epidemic prevention supervision institution. 14 days after the last sick pig is killed, upon passing the examination by the animal epidemic prevention supervision institution, the local veterinary administrative department shall apply to the people's government at the same level that originally issued the blockade order for lifting of the blockade.
4.2.8 Handling records
Complete and detailed records must be kept for the entire process of handling the epidemic for inspection.
5 Personnel involved in handling the epidemic shall wear protective clothing, rubber boots, masks, and gloves to protect themselves.