Prevention and treatment of Porcine circovirus Disease

Porcine circovirus belongs to the genus circovirus of the family circoviridae and is one of the smallest known animal viruses. The virion is 14-17nm in diameter, with an icosahedral symmetrical structure, no envelope, and contains a covalently closed single circular negative strand DNA. The genome size is about 1.76kb. PCV has a strong resistance to external physical and chemical factors, and can survive for a period of time even in the acidic environment of PH3 and the high temperature environment of 72 ℃. Chloroform has no hemagglutination activity. It is known that there are two serotypes of PCV, PCV1 and PCV2. PCV1 is a nonpathogenic virus. PCV2 is a pathogenic virus. Pigs are highly susceptible to PCV2. Infected pigs can expel the virus from nasal juice, feces and other wastes, and infect pigs of different ages through oral and respiratory pathways.

Clinical symptoms of porcine circovirus disease

1. Clinical symptoms of PMWS: the most common symptoms are progressive weight loss or growth retardation in pigs, which is also the necessary clinical basis for the diagnosis of PMWS. Other symptoms include anorexia, mental depression, movement retardation, pale skin, dishevelled coat, dyspnea and cough. The less common symptoms are diarrhea and disorders of the central nervous system. The incidence is generally very low and the fatality rate is very high. The superficial lymph nodes on the body surface are enlarged, and swollen lymph nodes can sometimes be touched, especially the superficial inguinal lymph nodes. Anemia and visual mucosal jaundice. All of the above clinical symptoms may not be seen in one pig, but all symptoms can be seen in diseased pigs. Gastric ulcers, somnolence, central nervous system disorders and sudden death are rare. Most PCV2 are subclinical infections. General clinical symptoms may be related to secondary infection, or may be caused entirely by secondary infection. In poor ventilation, overcrowding, air pollution, mixed culture and infection with other pathogens and other factors, the disease is significantly aggravated, the general case fatality rate is 10% to 30%.

2. Symptoms of congenital tremor: trembling ranges from mild to severe, and the number of infections in a litter of pigs also varies greatly. Severely trembling sick piglets often starve to death because they are unable to suck within a week after birth. Suckling pigs that had endured for 1 week survived and recovered at the age of 3 weeks. Trembling is bilateral, and the shivering stops when the suckling pig lies down or sleeps. External stimuli, such as sudden sound or cold, can cause or enhance tremors. Some pigs have been unable to fully recover and continue to tremble throughout the growing and fattening period. Diseased litter pigs are often born to newly introduced young breeding pigs, indicating that these seronegative pigs were exposed to PCV during the critical period of pregnancy.

3. Common mixed infection: PCV infection can cause immunosuppression in pigs, which makes the body more likely to be infected with other pathogens, which is also the reason for the mixed infection of circovirus and 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 S Ⅳ (swine influenza virus). Some of them are double infection or triple infection, and the case fatality rate of diseased pigs will also be greatly increased.

Defense mechanism of porcine circovirus disease

At present, there is no effective treatment for porcine circovirus disease, coupled with the decline in production performance and high mortality of affected pigs, which makes the disease particularly important. And because of the persistent infection of PCV2, the disease is more destructive economically. The application of antibiotics and good management are helpful to solve the problem of concurrent infection.

1. Strengthen feeding and management

Reducing feeding density, implementing strict all-in-all-out system and mixed group system, reducing environmental stress factors, controlling concurrent infection, ensuring stable immune status of pigs, strengthening biosafety 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. The patented disinfectant Virkon S can effectively kill circovirus when diluted at 1 ∶ 250, so it can be used for terminal disinfection between each batch of pigs.

2. Do a good job in immunization against major infectious diseases in pigs.

The occurrence of PCV2 and its related pig diseases requires additional conditions or common factors to induce clinical symptoms. The experience of countries all over the world in controlling this disease is to make appropriate active and passive immunization against common sources of infection, so it is key to vaccinate swine fever, swine pseudorabies, porcine parvovirus disease, asthma and blue ear disease in pig farms to ensure the safety of fetuses and suckling piglets. Therefore, it is very important for sows to implement reasonable immunization procedures according to different possible pathogens and different vaccines.

3. Artificial passive immunity

Serum therapy can be taken. The blood was collected from the fattening pigs in the pig farm (it is best to eliminate the breeding pig blood healthily), and the serum was separated and injected intraperitoneally to the weaning piglets.

4. the use of our own vaccine.

Once the disease occurs in the pig farm, the offal of the diseased pig can be processed into its own vaccine, according to clinical practice, the effect is good. But at the present stage, there are two viewpoints: first, sows and weaned piglets are immunized at the same time, which has the advantage of fast immune effect and can basically control the disease within 1 ~ 2 months. The disadvantage is that if the inactivation is not complete, the disease will exist for a long time. Second, only immunized weaned piglets, the advantage is that the immune safety is good, basically will 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.

5. Active immunity of "infected" substances

The "infected" substance refers to the feces of infected pigs, stillborn pigs and mummified fetuses in this pig farm, which can be used to feed sows, especially first-born sows, before mating, which can achieve better results. If sows with certain antibodies are given supplementary feeding after 80 days of pregnancy, a higher level of immunity can be produced and transmitted to piglets through colostrum. This method is not only effective in preventing and controlling the disease, protecting the health of fetal pigs and suckling pigs, but also has a good effect on reproductive disorders caused by other enteroviruses. However, the use of this method should be very cautious, if there are piglets in the farm will cause artificial infection.

6. Drug prevention

Prophylactic administration and treatment are very desirable for the control of bacterial mixed infection or secondary infection. But so far, the pathogen and mechanism of related pig diseases caused by PCV2 have not been fully understood, so we can not completely rely on specific control measures, only effective comprehensive measures can be carried out at the same time to achieve twice the result with half the effort.

① piglets were injected with Demixian (long acting oxytetracycline, 200 mg/mL, 0.5 mL each time) three times at 3,7 and 21 days of age, or 0.2 mL of Sujieling (ceftiofur 500 mg/mL) at 1, 7 days and weaning. From one week before weaning to one month after weaning, they were fed with Zhiyuanjing (50 mg/kg) + chlortetracycline or oxytetracycline or doxycycline (150 mg/kg) and drinking water with amoxicillin (500 mg/L).

② sows were fed with Zhiyuanjing (100mg/kg) + chlortetracycline or oxytetracycline (300mg/kg) one week before parturition and one week after parturition.

7. Comprehensive prevention and control plan

① delivery period: piglets are all in and out, and the two batches of pigs should be cleaned and sterilized. Wash sows and treat parasites before giving birth. Cross-lactation is restricted and, if necessary, within 24 hours after delivery.

② weaning period: the pigsty is small, in principle, a litter and a circle, the pigsty separation is strong. Adhere to a strict all-in-all-out, and have an independent fecal and urine excretion system separated from the neighbors. Reduce the feeding density: > 0.33m2 / pig. Increase feeder space: > 7 cm/ piglets. Improve air quality: NH3