Pathogen
Bacillus authracis belongs to the family Bacillaceae and Aerobic spore-forming bacillus. It is a long and straight large bacillus, positive for Gram stain, 3 to 5 μm long and 1 to 1.5 wide. Mm, capsule, no flagella, can not move. In the diseased animal body, there are single or 3 to 5 bacterial cells connected to form a short chain, and the bacterial cell junction is flat, such as a knife-cut or dimple, which is bamboo-like, and the free end is obtuse. A capsule can be formed in an animal, but a capsule is generally not formed on a common medium. Under anaerobic conditions, the bacteria die with the decay of the corpse, and the capsule can still remain, called "bacteria." In live anthrax carcasses or undissected corpses after death, no spores are formed. Once exposed to air, they are exposed to free oxygen, and spores can be formed at a certain temperature (12-24 ° C). The spores are oval or round, located in the center of the cells or slightly inclined to one end, not larger than the cells.
This bacteria is an aerobic bacteria. The optimum growth temperature is 30 to 37 ° C, and the optimum pH is 7.2 to 7.6. Nutritional requirements are not high and can grow in normal media. A long chain of ten to several bacterium cells is formed in a common medium. The colonies were flat grayish white with a rough surface. At low magnification, the edges of the colonies were curled. It grows well on blood agar plates and does not hemolyze. Bacillus anthracis can grow into hyphae or purple fungus in ordinary broth culture medium. The supernatant is transparent, and there are a lot of white flocculent precipitates in the tube. When it is shaken, the sediment gradually sinks and then sinks. The object is wound into a mass and is not easily broken. Gelatin puncture culture for 2 to 4 days, can be formed into a white inverted pine tree along the puncture line, and liquefied downward from the surface along the puncture line. Strong strains have strong liquefaction ability.
This strain can ferment glucose, produce acid without gas, and not ferment arabinose, xylose and mannitol. The VP test is positive, no sputum and H2S are produced, and nitrate can be reduced. When cultured in a solid (agar plate) or liquid (broth) medium at a dose of 0.05 to 0.5 IU of penicillin G per ml, the cells expand and adhere, and when the microscopic examination, the anthrax forms a beaded shape. A feature is often used for bacterial identification at the time of diagnosis.
Bacillus anthracis is present in carcasses, soil and water contaminated with anthrax. Bacillus anthracis exists in various organs, blood, lymphatic system, secretions and excretions after the death of sick animals. Among them, the spleen contains the most bacteria, and the blood contains the bacteria.
The propagating bacteria of Bacillus anthracis had weak resistance to the outside world and died in the undissected corpses in summer for 24 to 96 hours. It can survive for 6 to 15 hours under the sun and can survive for 1 month in dry blood. Heating at 70 ° C for 10 to 15 minutes, or boiling can immediately die. Bacillus anthracis can survive for 1 week in the bone marrow in the uncut body at a low temperature of -20 to 10 ° C for 3 weeks. A general disinfectant can kill the bacteria in a short time. However, the formation of anthrax spores is particularly strong, and in the dry state, it can survive for 30 to 50 years or more, and can survive for 100 hours under direct sunlight. It can survive for decades in anthrax contaminated soil, skin, hair and anthrax burial sites. If the temperature reaches 72-76 ° C in the manure, it can die within 4 days. It takes more than 15 minutes to boil, and it takes 10 to 15 minutes to autoclave at 121 °C to kill. The disinfectant is 5% carbolic acid for 1 to 3 days, 3% to 5% for Suer for 10 to 24 hours, and 4% of iodine for 2 hours to kill spores. On-site disinfection of livestock houses, utensils, feces, etc. can be disinfected with 20% bleaching powder, or 3% to 5% hot sodium hydroxide solution, 2% to 4% formaldehyde, 0.5% peracetic acid, 0.1% mercury solution. Bacillus anthracis-contaminated skin, immersed in 2% hydrochloric acid, 10% salt, 48 h at 30 ° C, 72 h at 18 ~ 22 ° C to achieve the purpose of disinfection.
Clinical symptoms
1. Recessive pigs have strong resistance to anthrax. Therefore, most of the anthrax in pigs are chronic, and there are no clinical symptoms. They are found only after meat hygiene inspection after slaughter. This is a common disease type of pig anthrax. .
2, subacute (pharyngeal) pigs eat Bacillus anthracis or spores, invading the pharynx and nearby lymph nodes and adjacent tissue mass reproduction, causing an inflammatory response. Mainly manifested as pharyngitis, elevated body temperature, depression, loss of appetite, obvious swelling of the neck and throat, mucous membrane blemishes, difficulty in swallowing and breathing, and inflexible neck activity. The mouth and nasal mucosa are blue-violet and finally suffocate and die. There are also cases that can be cured.
3, acute type (septic type) This type rarely occurs, changes, body temperature rises to 41.5. Above C, mental depression, day death, or sudden death.
Only a few reports in the country, mainly acute septicemia, loss of appetite, difficulty breathing, visible mucous membrane purple, 1 ~ 2
4, intestinal type This type is not as obvious as pharyngeal type, when the occurrence of intestinal anthrax, mainly manifests digestive dysfunction, constipation and diarrhea in sick pigs, even blood in the feces, severe cases can die, light can restore health.
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Diagnostic identification
Because pig anthrax is chronic or invisible, the clinical symptoms are not obvious, acute cases are rare, and necropsy is prohibited when anthrax or suspected anthrax occurs. The correct diagnosis of anthrax is very important, so laboratory examination and serological diagnosis are necessary.
1. The diagnostic value of clinical symptoms and epidemiological investigations is not significant. It is available for diagnosis in some areas for the occurrence of anthrax and the source of anthrax.
2, bacterial smear, microscopic examination is simple method is to treat the superficial blood vessels of the ear veins of the dead pigs or the extremities of the extremities to take blood, edema fluid, or spleen and diseased tissue to make a smear, with Giemsa or Wright's stain or Alkaline blue staining, microscopic examination, can be seen in a single or short chain (2 ~ 4 bacteria) connected to the capsular at both ends of the blunt bacillus, can be diagnosed. In the local lymph node smear of pigs, the morphology of anthrax is often atypical, and the thickness of the anthrax is not twisted. The bacteria disappears, and the capsules are visible. The bacteria are isolated and cultured. The fresh material is inoculated on the common agar plate. If it is contaminated or obsolete, it can be made into a suspension, heated at 70 °C for 30 min, killing non-spore bacteria and then inoculated and cultured; if it is a spoiled material, it can be made into a 1:10 emulsion to inoculate the mouse, and then The diseased material was inoculated and cultured, and the judgment was made according to the characteristics of colony growth.
If it is to be distinguished from the generic Bacillus cereus and Bacillus subtilis, a 7 phage lysis test, a capsule formation test, and an anthrax bead test can be performed.
4, animal infection test, the disease material is diluted 5 to 10 times with sterile physiological saline, subcutaneous injection of 0.1 ~ 0.2mL, or guinea pig 0.2 ~ 0.5mL, or rabbit 1mL, after 24 ~ 36h (mouse) or Inoculated animals died 2 to 4 days (guinea pig, rabbit). The smear of organs and blood of dead animals, through the Wright's staining microscopic examination, showed a large number of capsules of short-chain anthrax. Dead animals showed infiltration of the injection site and swelling of the spleen. It can also be used for culture and anthrax precipitation reaction check.
5, anthrax precipitation reaction (Ascoli's reaction) Take the diseased pigs a few grams of tissue, cut or smash, add 5 ~ lO times normal saline, boil for 10 ~ 15min, after cooling or filtration or centrifugation, take with a capillary pipette The clear liquid is slowly added along the tube wall into a thin glass tube containing the anthrax precipitated serum (finished product) to form a neat two-layer liquid surface, and a clear white precipitate ring is judged to be positive at the contact surface of the two liquids (reaction Appears within 1 to 2 minutes, preferably at 10 to 15 minutes). This reaction has high specificity, simple and rapid operation, and high detection rate. Even if the anthrax material is spoiled, a positive reaction can occur. The county and township veterinary hospitals (station) usually purchase a certain amount of sedimented serum and put it in the refrigerator for later use, which is of practical significance for timely diagnosis of the disease.
6, enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), etc. can also be used for the diagnosis of anthrax.
Pig disease prevention and control measures
One treatment For acute and subacute disease pigs, early diagnosis and timely treatment are important. Treatment of chronic anthracnose pigs is limited, but must be treated under strict isolation and personal care.
(1) Serum therapy Anti-anthrax serum is a special biological agent for the treatment of anthrax, and good results can be obtained at the beginning of the disease. The amount of large pigs is 50-100 mL, and the piglets are 30-80 mL. Half intravenously, half subcutaneously. The injection can be repeated once at 12h or 24h if necessary. To avoid allergic reactions, it is best to use anti-anthraquinone serum from the same animal. If the serum of a heterologous animal is used, 0.5 to 1 mL should be injected subcutaneously, and no specific reaction is observed after 0.5 hours.
Antibiotics and anti-anthrax serum are more effective at the same time.
(2) Antibiotics and sulfonamides are treated with penicillin. The pigs are injected 400,000 to 800,000 IU each time, twice a day for 2 to 3 days. Oxytetracycline 1 ~ 29, intravenous or intramuscular injection. Or penicillin is used together with oxytetracycline and tetracycline. Streptomycin, ciprofloxacin, doxycycline, lincomycin, gentamicin, cephalosporin, sulfathiazole, and sulfamethazine are also effective. The combination of penicillin and sulfonamide is more effective.
Intestinal anthrax also needs to be combined with oral Klein forest (smelly syrup), 3 times a day, and pigs are 2 to 5 mL each time.
It is also necessary to cooperate with symptomatic treatment and strengthen nursing work.
Second control measures
(1) For pigs in the area where the anthrax is often found or threatened, regular vaccination should be carried out every year to enhance the specific resistance of the pig. This is the fundamental measure to prevent this disease. There are two kinds of vaccines currently used in China.
Non-toxic anthrax spores: 0.5 mL of subcutaneous injection of pigs. Immunity was generated 14 days after the injection, and the immunization period was 1 year. No. II anthrax spore seedling: subcutaneous injection of 1 mL, 14 days after injection to produce immunity, the immunization period is 1 year.
(2) It is necessary to publicize to the masses that pigs that die for unknown reasons are not allowed to eat meat, and they cannot be shipped to the market for sale. They should be treated by veterinarians for inspection. It is forbidden to throw dead bodies everywhere and should be buried deep in the designated place. Slaughter plants and meat joint factories should strengthen the quarantine work on anthrax and strictly implement veterinary health measures.
(3) After the occurrence of pig anthrax, it should be reported to the competent department immediately to quickly identify the epidemic, make a diagnosis, and take resolute measures to fight the epidemic as soon as possible. 1 Delineation of epidemic areas and epidemic areas, isolation and blockade, and strict implementation of various measures at the time of blockade; half a month after the death or recovery of the last sick pig, report to the superior for approval to release the blockade and conduct a major sweeping and disinfection . 2 The sick pigs and suspected sick pigs are immediately injected with anti-anthrax serum or injected simultaneously with antibiotics for prevention and treatment. 3 Strictly disinfect contaminated pens and feeding management equipment; contaminated feed, manure, and waste are burned; bodies should be burned or buried deeply (bacteria die due to corpse corruption, but may also leave behind and retain pathogens. 4) In the slaughter inspection, when the pig anthrax is found, the production process is immediately stopped, and the whole plant or workshop is disinfected, and a certain number of slaughtered pigs before and after the detection of the sick pigs are harmlessly treated according to regulations. 5 Strengthen the protection work of the staff, and if there is an infected person, send it to the hospital for treatment as soon as possible.
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