The disease caused by pig circovirus 
(PCV-2) has caused great economic losses to the pig farming industry, so it has attracted more and more attention. Pig Circovirus Type 2 (PCV-2) is an important pathogen of piglets' post-weaning multisystem failure syndrome (PMWS), pig respiratory syndrome (PRDC), swine dermatitis and nephrotic syndrome (PDNS). It can also cause a variety of enteritis diseases, sow reproductive disorders and other diseases. This is a new viral infectious disease that has occurred in recent years. It has seriously endangered the development of the pig farming industry and should be taken seriously.
. Pathogen
porcine Circovirus (PCV) is a single strand cyclic DNA virus without encapsulation. In 1978, German scholar Tischer first isolated the virus from the pig renal cell line PK-15, and named it Pig Circovirus (PCV) in 1982. Ellis et al. (1998) first isolated a new virus from PMWS-affected pigs, similar to PCV isolated from PK-15 cell lines. Allan et al. (1999) referred to the PCV isolated from the diseased material as PCV-2. The PCV isolated from PK-15 cells is called PCV-1.
PCV is one of the smallest animal viruses known so far. PCV is highly resistant to the external environment. It can survive for 15 minutes at 70°C, but it cannot be inactivated at 56°C. Porcine cyclovirus type 2 (PCV-2) can induce apoptosis and T cell reduction in B cells (plasma cells) in the lymphatic system, putting pigs in an immunosuppressive state. Many studies have shown that PCV-2 is often infected with mixed infection with many other pathogenic microorganisms. Allan et al. (2000) believe that PCV-2 is often infected with parvovirus (PPV), reproductive disorder and respiratory syndrome virus (PRRSV), and pseudorabies virus (PRV), resulting in the failure of immunity in pigs, so PCV-2 is believed to be the primary virus.
. Epidemiology
The natural host of porcine circovirus PCV-2 is pig. Pigs of all ages and genders can be infected and can also lead to several types of diseases related to PCV-2 infection. For example, PMWS is mainly susceptible to weaning pigs. Suckling pigs rarely get sick. Generally, the incidence is concentrated in piglets 2 to 3 weeks after weaning and 5 to 8 weeks after weaning. Weaning stress may be an important inducing factor. PDNS mainly occurs in growing pigs and fattening pigs, and can also be seen in suckling piglets. PCV-2 can be infected through oral and respiratory tract routes. The infection rate of cohabitation with sick pigs without immunization can be as high as 100% (Allan et al., 1999). Viruses infected in sows can also be infected with piglets vertically through the placenta. Infected pigs can excrete viruses from nasal fluid, feces and other excrements. Causes the virus to spread among different pig individuals.
. Types and clinical symptoms of the disease caused by PCV-2 of the pig cyclovirus
.1 Multi-system failure syndrome (PMWS)
mainly occurs in piglets aged 5 to 12 weeks. The main clinical symptoms of this disease are reduced appetite or loss of appetite, pigs have progressive weight loss, difficulty breathing, diarrhea, anemia, sometimes pale skin or jaundice, delayed development, and weight loss. Because it is often mixed with PRRSV, PRV, etc. in clinical practice. This makes the clinical symptoms of this disease more complicated. The disease occurs slowly, and the onset of the pig herd can last for 12 to 18 months at one time. Antibiotic treatment is ineffective or poor.
.2 Porcine Respiratory Disease Syndrome (PRDC)
In most cases, this disease is regarded as a twin disease of PMWS. It is caused by a mixed infection of PRRSV or PRV and PCV-2, causing a syndrome of mixed infection of multiple pathogens and subsequent infection in an immunosuppressive state. The clinical symptoms are mainly manifested as cough and dyspnea. Sometimes some pigs have symptoms of flushing throughout the body and blood stasis and bleeding in the skin of the ear tip, tail end, femoral and forelimb fluid caused by microcirculation disorders, and blood stasis spots.
.3 Porcine dermatitis and nephrotic syndrome (PDNS)
This disease is characterized by skin lesions and fibrin necrotizing glomerulonephritis . It often occurs sporadically or breaks out in pig herds of 12 to 14 weeks old, and the onset of the pig herds can last for 12 to 24 months. The most common clinical symptom is round or irregular bulges in the skin. It presents a lesion with a red or purple surroundings with a black center. The diameter of the lesions is generally 2 cm, and some lesions often fuse into bands and plaques. It usually appears in the back drive, hind limbs and abdomen at the earliest. Then it can slowly expand to chest, ribs, ears and other parts. The mild-affected pig has normal body temperature and no abnormal behavior, and it often recovers automatically.The body temperature rises in severe cases of pigs. Decreased appetite. Weight loss. Suckling piglets are sometimes accompanied by diarrhea, anemia and jaundice when they occur. Finally, it can die.
.4 PCV-2 and sow breeding disorders
This disease has also occurred frequently in my country in recent years. The main targets of the disease are primary sows, mainly manifested as miscarriage, stillbirth, weak baby, stagnation of birth, prolonged estrus period, infertility, etc. The incidence of stillbirth and miscarriage in some serious sows is as high as about 60%.
.5 Congenital tremor of newborn piglets tremor
This disease mostly occurs in piglets born in sows, with an incidence rate of 1% to 3%, and is as high as about 10%. Generally, it occurs in the first week after birth, and tremors are bilateral, affecting bone and muscle development. The tremor disappears when you are lying down or sleeping. External stimulation (such as sound, temperature, etc.) can cause or aggravate tremors, and some continue to occur throughout the growth and development period. Affects the normal growth of piglets. Severe tremors can cause death from inability to feed breasts.
.6 Clinical pictures
. Pathological changes
Pathological changes vary greatly depending on the type of disease.
.1 Pigs with weaned piglets multisystem failure syndrome (PMWS) are usually thin after death, with mild to moderate pale skin, enlarged lymph nodes, white cuticles, and lymph node lesions in organs or tissues such as inguinal, mesenteric, bronchial, and other lymph node lesions are particularly prominent. The lungs are solid and rubbery, with spotty surfaces. The beige-brown lung lobes are in question with the normal pink lung lobes. In some cases, the liver manifestations are spotty and have varying degrees of atrophy, with fleshy faces, no congestion, and bile concentration. The kidney is enlarged and pale, and there is a visible white lesions under the renal capsule. Congestion or congestion in the cecum and colon mucosa. The spleen is enlarged and the texture is flesh-like. There have been reports of obvious spleen atrophy.
.2 Porcine
with porcine dermatitis and nephrotic syndrome (PDNS) has characteristic pathological changes such as systemic vasculitis and fibrin necrotizing glomerulonephritis.
.3 The pathological changes in porcine
with pig respiratory syndrome (PRDC) are mainly manifested in pathological changes such as lobular pneumonia, necrotic pneumonia, pleuropneumonia, pericarditis, serositis, pleural effusion and increased ascites.
.4 Pathological picture
. Diagnosis
Preliminary judgment can be made based on the type of disease caused by the pig circovirus PCV-2, its clinical symptoms and epidemiology, but the diagnosis must be based on laboratory diagnosis. Therefore, 3 conditions must be met for diagnosing this disease (with corresponding clinical symptoms; characteristic pathological changes: the antigen or nucleic acid of PCV-2 is detected from the disease material). At the same time, since the pathogens of synergistic or secondary infection are different in different pig farms, the pathogen properties of synergistic or secondary infection must be determined through laboratory diagnostic technology before a diagnosis can be made.
. To prevent diseases caused by
pig circovirus PCV-2, vaccines can be used for prevention. Due to the widespread existence of PCV-2 virus, people do not know in detail about its transmission mode, pathogenic mechanism, immune response mechanism, etc. We must adhere to the principle of prevention first and focus on strengthening feeding management and sanitation and epidemic prevention measures. To prevent the occurrence of epidemics. It is recommended that comprehensive prevention measures should be taken in production:
.1 Introduction and monitoring. No poisonous pig
self-bred and self-bred breeding pigs must also undergo antibody monitoring, and poisonous sows and breeding boars must be resolutely eliminated.
.2 Improve feeding methods
reduce feeding density, strengthen ventilation, implement a full inlet and all out feeding system, restrict foster care and prevent mixed breeding of pigs of different sources and ages. Reduce the chance of cross-infection of PCV-2 and other pathogens in pigs and minimize stress factors.
6.3 Do a good job in immune prevention of related epidemics, strictly implement biosafety measures, and control concurrent infections.
6.4 Improve the nutritional level of the pig herd and enhance the pig herd's own disease resistance.
6.5 Comprehensive therapy is used during treatment.
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