Porcine circovirus discovery and introduction

In 1974, the German Tischer found that porcine circovirus (PCV) for icosahedral symmetry, no capsule, single stranded circular DNA virus. Known as one of the smallest animal viruses. The diameter of the virus particle is 14-17nm, and it is a 20-face symmetric structure with no capsule. It contains covalently closed single-stranded negative-strand DNA with a genome size of about 1.76kb.

PCV resistance to physical and chemical factors outside the very strong, even in PH3 acidic environment and 72 ℃ high temperature environment can survive for some time, the role of chloroform is not lost, no blood clotting activity. PCV is now known to have two serotypes, namely PCV1 and PCV2. PCV1 is a non-pathogenic virus. PCV2 is a pathogenic virus. Pigs have a strong susceptibility to PCV2, pigs infected with swine from the nasal fluid, feces and other waste from the virus, the oral cavity, respiratory tract infection of pigs of different ages.

Epidemiology of porcine circovirus

PMWS is the earliest recognized and confirmed by the PCV2 infection caused by disease. Common PMWS occurs mainly in 5 to 16 weeks of age pigs, the most common in 6 to 8 weeks old pigs, little infection piglets. Usually 2 to 3 days after weaning or 1 week after the onset of acute onset in pigs, the fatality rate of up to 10%, resistance to late development of pigs was significantly blocked. But often due to concurrent or secondary bacterial or viral infection leaving the mortality rate greatly increased, the mortality rate of up to 25%. Seroprevalence of PCV was found worldwide.

The positive rates of PCV antibodies in swine herds were as high as 95% and 55% in Germany and Canada, respectively. In the UK and Ireland, the positive rates of PCV antibodies were 86% and 92%, respectively, but not necessarily PMWS symptoms. In China, the positive rate of 20-day-old weaned piglets was 0, the positive rate of weaning piglets was 16.5%, the positive rate of gilts was 42.3%, the positive rate of sows was 85.6 %, Finishing pigs positive rate was 51%, the total positive rate was 42.9%. Clinical symptoms may persist in a few months, peaked at 6 to 12 months, then decreased; a group and another group of infections are very different, because suckling pig maternal PCV antibody after birth in 8 ~ 9 weeks of age disappeared, and pig transfer to the fattening circle (11 to 13 weeks of age) and exposure to PCV, PCV antibodies appeared again.

Pathogenesis of porcine circovirus

PCV particles were present in nasal mucosa, bronchus, lung, tonsil, kidney, spleen and small intestine. Thymus, spleen, mesentery, bronchus, etc. in the lymphoid tissue of the virus, including lung and lymph node detection rate was higher. The results showed that PCV seriously infested the immune system of pigs: virus and macrophages / monocytes, histiocytes and thymus macrophages, accompanied by decreased body condition caused by the formation of immune suppression.

Immunodeficiency due to immunosuppression, its clinical manifestations: the low pathogenicity or weaken the vaccine can cause disease of microorganisms; repeated onset of treatment on the non-responsive; vaccination does not have a sufficient immune response; in a litter of pigs Of unexplained morbidity and mortality at birth, and multiple disease syndromes in the herd. All of these characteristics occurred in the PMWS pig herds in different degrees.

Lymphocyte depletion and macrophage infiltration in lymphoid tissue is the unique pathologic damage and basic feature of PMWS. And this feature is associated with a decrease in B and T cells in the blood circulation and reduction of such cells in lymphoid organs; and is highly correlated with the increase in macrophage / monocyte lineage cells in peripheral blood and lymphoid tissue. In addition, a large number of PCV2 antigens have been identified in lymphoid tissue, related immune cells and cells in blood.

Porcine circovirus transmission

Pigs have a strong susceptibility to PCV2, pigs infected with swine from the nasal fluid, feces and other waste from the virus, the oral cavity, respiratory tract infection of pigs of different ages. Pregnant sows infected PCV2, the vertical transmission of infection through the placenta piglets. Artificial infection of PCV2 seropositive boar semen contains PCV2 DNA, indicating that semen may be another route of transmission. With PCV2 artificial infection test pigs, other uninsured pigs cohabitation infection rate was 100%, indicating that the virus can spread horizontally. Pig movement among different groups of pigs is the main route of transmission of the virus can also be contaminated clothing and equipment to spread.

The breeding methods may be related to the disease, feeding and management, poor weaning environment, different sources and age of pig mixed group, high stocking density and stimulate the immune system of piglets are an important risk factor for the disease induced, but the pig farm Size is not important.

PCV infection in experimental animals, found only pigs to produce specific antibodies, and rabbits, rats, cattle, and even per capita seronegative.

PCV1 is not pathogenic to pigs but produces serum antibodies and is ubiquitous in the investigated herd.

PCV2 can cause weaned piglet multiple system failure syndrome (PMWS), and more in 5 to 16 weeks old pigs.

PCV levels can spread, contact with the virus one week after the serum can be detected in the antibody, followed by increasing the titer.

Mechanism of porcine circovirus defense

The disease is no effective treatment, coupled with decreased pig performance and high mortality, so that the disease is particularly important. And because PCV2 sustained infection, so that the disease in the economy with greater destructive. The application of antibiotics and good management can help solve the problem of concurrent infection.

1, to strengthen feeding and management

2, do the main infectious diseases of pig immunization

3, artificial passive immunity

4, the use of their own vaccines

5, "infection" active immunization of substances

6, drug prevention