How long can circovirus survive in pigs and how to kill it?

Porcine circovirus belongs to circoviridae circovirus, with a particle size of 14 ~ 25 nm and an average diameter of 17 nm. It is a symmetrical icosahedron with no envelope, and its genome is a single-loop DNA composed of deoxyribonucleic acid. Its suspension density in tissues is 1.37 cm3, and that in sedimentation coefficient is 52S, which is the smallest animal virus found so far. The replication of PCV is rolling circle replication, which firstly goes through a double-stranded replication type (RF), and then the protein is transcribed by the double-stranded replication type. This replication mode is the same as that of avian infectious anemia virus (CAV). PCV particles exist in nasal mucosa, bronchus, lung, tonsil, kidney, spleen and small intestine of sick pigs. The virus exists in lymphoid tissues of thymus, spleen, mesentery and bronchus, and the detection rate in lung and lymph nodes is high. The results showed that PCV seriously invaded the pig's immune system: the virus was accompanied by macrophages/monocytes, histiocytes and thymocytes, which led to the decline of pig's physique and the formation of immunosuppression. Immunodeficiency is caused by immunosuppression, and its clinical manifestations are as follows: diseases can be caused by microorganisms with low pathogenicity or attenuated vaccines; Recurrent diseases do not respond to treatment; Insufficient immune response to vaccination; More than one pig in a litter has unexplained birth and death; There are multiple disease syndromes in pigs at the same time. These characteristics basically appear in pigs of PMWS to varying degrees. Lymphocyte loss and macrophage infiltration in lymphoid tissue are the unique pathological damage and basic characteristics of pigs with PMWS disease. Moreover, this feature is highly related to the decrease of B and T cells in blood circulation and the decrease of such cells in lymphatic organs. It is highly correlated with the increase of macrophage/monocyte lineage cells in peripheral blood and lymphoid tissue. In addition, it has been confirmed that there are a large number of PCV2 antigens in lymphoid tissues, related immune cells and cells in blood. PMWS is the earliest recognized and confirmed disease caused by PCV2 infection. Common PMWS mainly occur in pigs of 5 ~ 16 weeks old, most commonly in pigs of 6 ~ 8 weeks old, and rarely infect suckling pigs. Generally, the onset of the disease begins 2 ~ 3 days after weaning or 1 week. In acute pigs, the mortality rate can reach 10%, and the late development of resistant pigs is obviously hindered. However, due to concurrent or secondary bacterial or viral infections, the mortality rate often increases greatly, and the mortality rate can reach more than 25%. Serological investigation shows that PCV is prevalent all over the world. In Germany and Canada, the positive rates of PCV antibody in pigs are as high as 95% and 55% respectively, and in Britain and Ireland, the positive rates of PCV antibody in pigs are as high as 86% and 92% respectively, but they do not necessarily show PMWS symptoms. In some provinces and cities in China, the positive rate of 20-day-old weaned piglets is 0, 1 ~ 2-month-old weaned piglets is 16.5%, the positive rate of reserve sows is 42.3%, the positive rate of multiparous sows is 85.6%, the positive rate of finishing pigs is 5 1%, and the total positive rate is 42.9%. Clinical symptoms may last for several months, peak in 6 ~ 12 months, and then decline; There is a great difference in infection between one group and the other, because the maternal PCV antibody of suckling pigs disappears at 8-9 weeks after birth. When piglets are transferred to fattening circle (1 1- 13 weeks), they are exposed to PCV again, and the PCV antibody reappears. Pigs are susceptible to porcine circovirus type 2. Infected pigs can excrete viruses from nasal fluid, feces and other wastes, and infect pigs of different ages through oral and respiratory routes. Pregnant sows infected with PCV2 can infect piglets vertically through the placenta. The semen of artificially infected boar with negative serum of PCV2 contains DNA of PCV2, which indicates that semen may be another route of transmission. After the experimental pigs were artificially infected with PCV2, the cohabitation infection rate of other unvaccinated pigs was 100%, which indicated that the virus was horizontal transmission. The movement of pigs between different herds is the main route of virus transmission, and it can also be spread through contaminated clothes and equipment. Factory farming may be related to this disease. Poor feeding management, bad weaning environment, mixed pigs from different sources and different ages, high feeding density and stimulation of immune system of piglets are all important risk factors of this disease, but the size of pig farm is not important. PCV infected experimental animals and found that only pigs produced specific antibodies, while rabbits, rats, cows and even people were seronegative. PCV 1 is not pathogenic to pigs, but it can produce serum antibodies, which are widely present in the investigated pigs. PCV2 can cause multiple system failure syndrome (PMWS) in weaned piglets, mostly in pigs of 5 ~ 16 weeks old. PCV can be transmitted horizontally. After a week of exposure to the virus, antibodies can be detected in serum, and then the titer continues to increase. The most common clinical symptom of PMWS is progressive emaciation or growth retardation in pigs, which is also a necessary clinical basis for the diagnosis of PMWS. Other symptoms include anorexia, depression, bradykinesia, pale skin, unkempt coat, dyspnea and respiratory disorder characterized by cough. Less common symptoms are diarrhea and central nervous system disorder. The incidence rate is generally low and the mortality rate is high. Superficial lymph nodes on the body surface are swollen, and sometimes swollen lymph nodes can be touched, especially superficial inguinal lymph nodes; Anemia and visible mucosal jaundice. All the above clinical symptoms may not be seen in a pig, but all the symptoms can be seen in a sick pig. Gastric ulcer, lethargy, central nervous system disorder and sudden death are rare. The vast majority of PCV2 are subclinical infections. General clinical symptoms may be related to secondary infection, or completely caused by secondary infection. In the case of poor ventilation, congestion, air pollution, polyculture and infection with other pathogens, the illness is obviously aggravated, and the general mortality rate is 10% ~ 30%. Symptoms of congenital tremor vary from mild to severe, and the number of infections in a litter of pigs also varies greatly. Sick piglets with severe shivering often starve to death because they cannot suck milk after birth 1 week. A suckling pig that has endured 1 week can survive and recover in 3 weeks. The tremor is bilateral, and the tremor stops when the suckling pig lies down or sleeps. External stimuli, such as sudden sounds or cold, can cause or aggravate shivering. Some pigs have been unable to fully recover and continue to tremble throughout the growth and fattening period. Infected pigs are usually born to newly introduced young breeding pigs, which indicates that these seronegative breeding pigs are exposed to PCV during the critical period of pregnancy. The common mixed infection of PCV can cause immunosuppression in pigs, making the body more susceptible to other pathogens, which is also the reason why circovirus is mixed with many diseases in pigs. The most common mixed infections are PRRSV, PRV (Pseudorabies Virus), PPV (Parvovirus), Mycoplasma pneumoniae, Pasteurella multocida, PEDV (Epidemic Diarrhea Virus) and SIV (Swine Influenza Virus), some of which are double infection or triple infection, and the mortality rate of sick pigs will be greatly increased, and some of them can reach 25% ~ 40%. Edit the pathological changes in this paragraph and dissect the pathological changes. The main pathological changes of the disease are emaciation, anemia, pale skin and jaundice in pigs (20% pigs suspected of PMWS appear); The lymph nodes are abnormally enlarged, and the visceral and peripheral lymph nodes are enlarged to 3 ~ 4 times the normal volume, and the sections are evenly white; There is taupe inflammation and swelling in the lungs, showing diffuse lesions, increased specific gravity and hard rubber-like; The liver is dark in color, pale yellow to orange in appearance, with atrophy between hepatic lobules and hyperplasia of connective tissue; Renal edema (some up to 5 times normal), pale face, necrotic focus under the capsule; The spleen is slightly swollen and the texture is like meat; The pancreas, small intestine and colon often have swollen and necrotic lesions. Histological lesions are widely distributed in organs and tissues of the whole body, with extensive pathological damage. Mild multifocal or highly diffuse interstitial pneumonia in the lungs; The liver has hepatitis characterized by single cell necrosis of hepatocytes; The kidney has mild to severe multifocal interstitial nephritis; The heart has multifocal myocarditis. Diversity granulomatous inflammation often occurs in lymph nodes, spleen, tonsils and thymus. Lymphocyte loss is the main histopathological change in pigs with PMWS disease. The diagnosis of this disease must be combined with clinical symptoms, pathological changes and laboratory pathogen or antibody detection to get a reliable conclusion. The most reliable method is virus isolation and identification. Pathological examination after the death of sick pigs has important diagnostic value. The disease should be suspected when it is found that the whole body lymph nodes of dead pigs are enlarged, the lungs are not completely degenerated or coagulated and dense lesions are formed. It can be seen that lymphocytes in lymphoid tissue decrease and mononuclear phagocyte-like cells infiltrate to form multinucleated giant cells. If basophilic or amphoteric cytoplasmic inclusions are found in these cells, diagnosis can be basically made. Serological examination is an effective means of prenatal diagnosis. Indirect immunofluorescence (IIF), immunoperoxide monolayer culture, ELISA, polymerase chain reaction (PCR), nucleic acid probe hybridization and in situ hybridization (ISH) were used to diagnose the disease. IIF method is suitable for the detection of PCV in cell culture. In PK- 15 cells, histopathological materials were used as coverslips, fixed with acetone, and PCV in cell culture was reacted with rabbit anti-PCV hyperimmune serum, so that PCV could be detected and typed. ELISA can be used to detect virus antibodies in serum. A competitive ELISA method was established with cell culture virus (PCV2) as antigen and PCV2 specific monoclonal antibody as competitive reagent. The detection rate of competitive ELISA was 99.58%, while that of indirect immunofluorescence was only 97. 14%. The method can be used for large-scale monitoring of PCV2 antibody. PCR is a rapid, simple and specific diagnostic method. PCV2-specific or group-specific primers are used to amplify genes from tissues, nasal secretions and feces of sick pigs. According to the restriction endonuclease map and the base sequence of the amplified product, PCV infection was confirmed. There is also a simple PCR (multiplex PCR method. This method can be used to detect the nucleic acid of porcine circovirus. However, PCV 1 and PC v2 can not be distinguished. PCV2 has population specificity, can accurately locate the position of PCV in tissues and organs, and can be used for clinical material detection and pathological analysis. Clinical diagnosis points (1)PMWS mainly occur in pigs of 5 ~ 16 weeks old and grow well before weaning. (2) Piglets in the same litter or in different litters have respiratory symptoms, diarrhea, growth retardation and weight loss. Sometimes there will be pale skin or jaundice. Antibiotic therapy is ineffective or ineffective. (3) Lymph node enlargement, splenomegaly, pulmonary enlargement, extensive interstitial changes, and scattered brown mutation areas of different sizes on the surface. Other organs may also have different degrees of lesions and injuries. At present, there is no effective treatment for the disease, and the decline of pig production performance and high mortality make the disease particularly important. In addition, due to the persistent infection of PCV2, the disease is more destructive economically. The application and good management of antibiotics are helpful to solve the problem of concurrent infection. Strengthening feeding management, reducing feeding density, implementing strict all-in and all-out system and mixed group system, reducing environmental stress factors, controlling concurrent infection, ensuring the stability of pigs' immune state, strengthening biological safety measures inside and outside pig farms, and ensuring that pigs come from clean pig farms when buying pigs are effective measures to prevent and control the disease and reduce economic losses. Patent disinfectant Virkon S can effectively kill circovirus when diluted in 1∶250, so it can be used for terminal disinfection between each batch of pigs. Do a good job in immunization against major infectious diseases in pigs. The occurrence of PCV2 and its related pig diseases needs other conditions or the same factors to induce clinical symptoms. At present, the experience of controlling the disease in the world is to give appropriate active and passive immunity to the same source of infection. Therefore, immunization against swine fever, pseudorabies, parvovirus, asthma and blue ear disease in pig farms is the key to ensure the safety of fetuses and suckling piglets. Therefore, according to different possible pathogens and different vaccines, it is very important to implement reasonable immunization procedures for sows. Artificial passive immunity can adopt serum therapy. Collect blood from fattening pigs in pig farms (it is best to eliminate the blood of breeding pigs healthily), separate serum and inject it into weaned piglets. The use of local vaccines Once the disease occurs in pig farms, the sick pig viscera can be processed into local vaccines. According to clinical practice, the effect is good. But at this stage, there are two viewpoints: first, sows and weaned piglets are immunized at the same time, which has the advantage of quick immune effect and can basically control the disease within 1 ~ 2 months; The disadvantage is that if inactivation is not complete, the disease will exist for a long time. Secondly, only the weaned piglets are immunized, which has the advantage of good immune safety and basically does not make the disease exist for a long time; The disadvantage is that the immune effect is slow, and it takes about half a year to control the disease. Active immunization of "infected" substances "infected" substances refer to the feces of infected pigs, stillborn pigs, mummified fetuses, etc. Used to feed sows before breeding, especially primiparous sows, can get good results. If sows with certain antibodies are supplemented after 80 days of pregnancy, they can produce higher immune level and pass it on to piglets through colostrum. This method can not only effectively prevent and control the disease, protect the health of fetal pigs and suckling pigs, but also have a good effect on reproductive disorders caused by other enteroviruses. But this method should be used very carefully. If there are piglets in the field, it will cause artificial infection. Drug prevention, preventive administration and treatment are ideal for controlling mixed infection or secondary infection caused by bacteria. But up to now, the pathogen and pathogenesis of related pig diseases caused by PCV2 are not completely clear, so we can't rely entirely on specific control measures, and only effective comprehensive measures can get twice the result with half the effort. The following drug prevention schemes can be tried out: piglet medication: suckling piglets are injected with Mixian (long-acting oxytetracycline, 200 mg/mL, 0.5mL)3 each time) for 3 times at the age of 3, 7, 2 1 day, or injected with Kuaijieling (ceftiofur, 500mg/ml) for 0.2ml at the age of 1 day and 7/day. Feed Zhiyuan Jing (50 mg/kg)+ chlortetracycline or oxytetracycline or doxycycline (1 50 mg/kg) and drink amoxicillin (500 mg/L) respectively from before weaning 1 week to after weaning/month. Medication for sows: Add Zhiyuan Jing (1 00 mg/kg)+chlortetracycline or oxytetracycline (300 mg/kg) to the feed before delivery and after delivery. Comprehensive prevention and control plan delivery period: all piglets are in and out, and cleaning and disinfection should be carried out between the two batches of pigs; Cleaning sows before delivery and dealing with parasites; Limit cross-breastfeeding, if necessary, within 24 hours after delivery. Weaning period: the pigsty is small, in principle, a nest and a circle, and the pigsty is firmly separated; Adhere to strict all-in and all-out, and have an independent drainage system separated from neighbors; Reduce the feeding density: > 0.33 m2/ head; Increase the feeding space: > 7 cm/ piglet; Improving air quality: NH3