The disease is characterized by reproductive problems in pregnant sows (abortion, stillbirth, mummy) and respiratory diseases in pigs of all ages, especially piglets. It has now become one of the major diseases in large-scale pig farms.

This disease has been referred to as "mysterious pig disease", "new swine disease", "pig epidemic abortion and respiratory syndrome", "porcine reproductive and respiratory syndrome", "blue ear disease", "pig plague", etc. It is classified as a second-class infectious disease.

First, the pathogen

The porcine reproductive and respiratory syndrome virus is a single-stranded positive-stranded RNA virus belonging to the genus of nested viruses, arteriviruses, and arteriviruses. Does not agglutinate mammalian or avian red blood cells, has strict host specificity, and is monophilic to macrophages. The proliferation of the virus has an antibody-dependent enhancement effect, and in the presence of neutralizing antibody levels, the ability to replicate on the cell is instead enhanced.

Second, Epidemiology

The disease is a highly contagious disease that is epidemic. PRRSV only infects pigs, and pigs of all breeds, ages, and uses can be infected. However, pregnant sows and piglets less than one month old are the most susceptible. Affected pigs and infected pigs are an important source of infection. The main route of transmission is contact infection, airborne transmission and semen transmission, and it can also be transmitted vertically through the placenta. Susceptible pigs can be infected by oral, nasal, intramuscular, intraperitoneal, intravenous, and intrauterine vaccination. After 2 to 14 weeks after the virus is infected in pigs, the virus can be transmitted to other susceptible pigs through contact. Viruses can be detected in the nasal cavity, feces and urine of infected pigs. Susceptible pigs may be infected by direct contact with infected pigs or by contact with transport vehicles or devices contaminated with PRRSV. The flow of infected pigs is also an important means of transmission of the disease.

Persistent infection is an important feature of PRRS epidemiology. PRRSV can exist in infected pigs for a long time.

Third, the pathogenesis

PRRSV can pass through the placenta through the blood circulation to infect the fetus, causing reproductive problems such as miscarriage of sows in late pregnancy.

Fourth, clinical symptoms

The incubation period of this disease is quite different, and the latency period for PRRS infection in susceptible herds after infection is introduced. The shortest period is 3 days and the longest is 37 days. The clinical symptoms of the disease vary greatly and are affected by the virus strain, immune status, and feeding and management factors and environmental conditions. Low-violence strains can cause prevalence of no clinical symptoms in pigs, while virulent strains can cause serious clinically diagnosed diseases, and can be classified into acute type, chronic type, and sub-clinic type.

1. Acute type: Sick sows mainly manifest as depression, loss of appetite or waste, fever, different degrees of dyspnea, late pregnancy (105-107 days), sows abortion, premature birth, stillbirth, mummification, Weaker. Sows have an abortion rate of 50% to 70%, a stillbirth rate of 35% or more, and mummification of up to 25%. Some newborn piglets exhibit dyspnea, dyskinesia, and mild paralysis. The mortality rate is significantly higher in the first week after birth. (40% to 80%). A small number of sows showed no post-partum abortion, increased retention of placenta, and increased vaginal discharge.

One-month-old piglets showed typical respiratory symptoms, dyspnea, sometimes abdominal breathing, loss of appetite or obsolescence, increased body temperature above 40°C, and diarrhea. Coarse hair, ataxia, gradual weight loss, eyelid edema. A small number of piglets showed visible ear and body skin bleeds. The mortality of piglets before weaning can reach 80% to 100%. The weight gain of piglets after weaning is reduced, and the daily gain can be reduced by 50% to 75%. The mortality rate is increased ( 10% to 25%). Resistant to pig growth is slow, easy to secondary to other diseases.

Growing pigs and finishing pigs showed mild clinical signs, respiratory symptoms with different procedures, and a few cases showed coughing and dark purple on the back, sides, abdomen and tail of the ears. Infected pigs are prone to secondary infections and have corresponding symptoms.

The incidence of boars is relatively low, mainly as a general clinical symptoms, but boar semen quality is reduced, sperm abnormalities, semen can be toxic.

2. Chronic type: This is the main form of PRRS performance in large-scale pig farms. Mainly manifested as the decline in the performance of the pigs, slow growth, reproductive performance of the sow herds, decreased immune function of pigs, easy to secondary infection of other bacterial and viral diseases. The incidence of respiratory diseases in pigs, such as mycoplasma infection, infectious pleuropneumonia, streptococcal disease, and eperythrozoonosis, has increased.

3, sub-clinic type: infected pigs are not disease, manifested as persistent infection of PRRSV, pigs serological antibody positive, the positive rate is generally 10% to 88%.

V. Pathological changes

1, gross lesions: no cases of secondary infection except mild or moderate lymph nodes edema, the naked eye changes are not obvious, the pathological changes in the respiratory tract is mild to severe interstitial pneumonia, sometimes catarrhal pneumonia, if any With secondary infection, there may be corresponding pathological changes such as pericarditis, pleurisy, peritonitis, and meningitis.

2. Histopathology: There are few characteristic lesions in piglets and fetuses produced by reproductive disorders caused by infection with PRRSV, and fetal lesions caused by PRRS are the result of aseptic autolysis in the uterus and no specificity appears; aborted fetal blood vessels surround Arteritis, myocarditis and encephalitis characterized by infiltration of macrophages and lymphocytes occur. Umbilical cord hemorrhagic expansion and necrotizing arteritis.

The more common characteristic histopathological changes of growing pigs than adult pigs, the histological lesions of the lungs are universal and have diagnostic significance. Pneumonia caused by simple PRRS infection is characterized by interstitial pneumonitis with normal respiratory epithelium. It is characterized by alveolar septum thickening, mononuclear cell infiltration and type II epithelial cell proliferation, and necrotic cell debris in the alveolar space.

When PRRS is mixed with bacteria and viruses, the lesions should be different from the bacteria/viruses that are complicated by infection. The co-infection of bacterial pathogens often causes complex PRRS pneumonia. Interstitial pneumonia is often mixed with purulent cellulose bronchial pneumonia or It is covered by purulent cellulose bronchial pneumonia. Some infections also show pleurisy.

The lesions of the nasal turbinate mucosa are characteristic of the late PRRS infection with epithelial cell cilia loss, epithelial vacuolization and submucosal lymphocyte, macrophage and plasma cell infiltration. Histopathological changes of lymph nodes, thymus, and spleen were characterized by hypertrophy and hyperplasia, central necrosis, and infiltration of multinucleated giant cells in the lymphatic sinus. The spleen white pulp, tonsillar follicular lymphocyte necrosis, and late splenic lymph node cells were seen early in the disease. Hyperplasia; In addition, PRRS infection caused by the vascular, nervous system, reproductive system lesions are mainly manifested as lymphoid, macrophage, plasma cell proliferation and infiltration.

Six, differential diagnosis

The disease should be differentially diagnosed with other reproductive and respiratory diseases, such as pseudorabies, porcine circovirus disease, porcine parvovirus disease, swine fever, porcine Japanese encephalitis, porcine respiratory coronavirus disease, porcine brain Myocarditis, porcine hemagglutinating myelitis, and other bacterial diseases are distinguished.

Seventh, prevention and control

1. Stick to the principle of self-cultivation and self-cultivation and establish a stable breeding herd, which is not easy to introduce. If it is necessary to introduce, we must first find out the epidemic of the pig farm that was introduced. In addition, serological tests should be carried out. Negative pigs should be introduced, and the introduction of positive pigs should be strictly prohibited. After introduction, appropriate isolation zones must be established and monitoring work must be done. Generally, it takes 4 to 5 weeks for isolation and quarantine. Healthy people can only feed in groups.

2. In order to fully realize all-in and full-out, large-scale pig farms should at least have two stages of delivery and conservation.

3. Establish and improve the biosecurity system for large-scale pig farms, regularly disinfect the pig houses and the environment, and maintain the cleanliness and hygiene of pig houses, feeding management tools and the environment. On the one hand, it can prevent the spread of external diseases, and on the other Hygienic disinfection measures minimize the contamination of pathogenic microorganisms in the farm, which can minimize and reduce the incidence of PRRSV-infected herds and secondary infections.

4, do a good job feeding pigs and management. In pig farms infected with porcine reproductive and respiratory syndrome virus, feeding and management of the pigs at each stage should be well done to ensure the nutritional level of the pigs, so as to increase the resistance of the pigs to other pathogenic microorganisms and thus reduce secondary diseases. The incidence of infection and the resulting loss.

5. Do a good job of immunization against other diseases and control other diseases, especially the control of swine fever, pseudorabies and swine asthma. In pig farms infected with porcine reproductive respiratory syndrome virus, best efforts should be made to control swine fever, otherwise it will result in high mortality rate of pigs. At the same time, immunization against swine asthma vaccine should be implemented to reduce the risk of M. hyopneumoniae infection. Invade the lungs, thereby increasing the resistance of the pig's lungs to respiratory pathogen infections.

6. Regularly monitor the status of the infection of porcine reproductive and respiratory syndrome virus in pigs to understand the status of the disease on the farm. In general, once a quarterly monitoring, the pigs in each stage are sampled for antibody monitoring. If there is no significant change in the positive rate of the four monitoring antibodies, it indicates that the disease is stable on the farm, on the contrary, if it is in a certain quarter. The increase in the positive rate of antibodies indicates that there are problems in the management and disinfection of farms. Should be corrected.

7. Strictly seal the infected pig farms; take certain measures on the pig farms around the affected pig farms to avoid the spread of disease; do no harm treatment for the abortion fetuses, stillbirths, and dead pigs; thoroughly disinfect the maternity ward; Diseased pigs, symptomatic treatment, improved feeding conditions, etc.

8. Regarding vaccination, in general, there are no effective immune control measures. Currently, commercial PRRS attenuated vaccines and inactivated vaccines have been introduced at home and abroad, and domestically approved inactivated vaccines are also available. However, the phenomenon of increased virulence of PRRS attenuated vaccines and safety issues have caused increasing concern. There are many outbreaks of PRRS in pigs that use attenuated vaccines at home and abroad. Therefore, live vaccines should be used with caution. Although the immune efficacy of inactivated vaccines is limited or uncertain, there is no problem in terms of safety. Therefore, in infecting pig farms, inactivated vaccines can be considered for sows.

VIII. Drug Control

The disease focuses on prevention and should control the infection of stress and other diseases. The effective prevention procedures are now recommended as follows:

1. Boars are to be prevented once a month or quarterly: 500g of Blue Circle Conti 500g + Zhiyuan must be added to each ton of feed for 7 days.

2. Sows are pregnant for 70-80 days, 7 days before delivery and 7 days after delivery: 500g of blue round Kangtai and 500g of Zhiyuan must be added per ton of feed.

3, sows on the day of weaning to 7 days: Add 500g of blue circle Kangtai per ton of feed and 500g of Zhiyuan will be fed continuously.

4. 7 to 15 days before gilts are mated: Add 500g of Blue Circle Conti 500g + Zhiyuan must be added to the feed per ton of feed. Feed it continuously.

5. 3 days before weaning and 2 weeks after weaning: add 500g of blue round Kangtai 500g per ton of feed.

6, 18 weeks and 22 weeks of age were used for one week: 500g of blue round Kangtai 500g + Zhiyuan must be net per ton of feed, feeding continuously.

7. Disinfect twice a week: Quick clean 1:500 dilution with pig spray.

Twice a month for fumigation: Quick-clean 1:25-fold dilution with pig fumigation, each bottle (500ml) can fumigate 1250 cubic meters.

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