Diagnosis, Treatment, and Prevention of Porcine Reproductive and Respiratory Syndrome

Porcine reproductive and respiratory syndrome (PRRS), also known as swine blue ear disease, is caused by the porcine reproductive and respiratory syndrome virus in the family Arteriviridae. The form of harm caused by this disease has shifted from being mainly reproductive disorders in sows to being mainly respiratory syndrome in nursery pigs. The disease was introduced into China from abroad and is an infectious disease that severely affects the @#@227@#@ industry. Its clinical symptoms are mainly characterized by reproductive disorders, difficulty breathing, blue-purple ears, and concurrent other infectious diseases. The disease currently presents new clinical symptoms, such as eyelid edema, subcutaneous edema, thickened skin on the ears, intense itching of the mouth and nose, diarrhea, muscle tremors, ataxia, and hindquarter paralysis. Because the large temperature difference and abnormal climate in spring and winter trigger this disease, and because there is currently no specific therapeutic drug, it is very necessary to do a good job of preventing this disease.

Epidemic Characteristics

Under normal circumstances, porcine reproductive and respiratory syndrome has no obvious seasonality, but the incidence rate is relatively high in winter and spring. The main transmission route of the disease is the respiratory tract. Infected pigs and virus-carrying pigs can shed the virus into the air and contaminate the surrounding environment. If disinfection measures are not adequate, the virus can persist in pig houses for a long time. Sudden climate changes and the introduction of pigs often become triggering factors for this disease.

Clinical Features

1. Sows are divided into acute and chronic types

Acute infection: persistent high fever, lethargy, body temperature 40-41.5°C, accelerated heart rate (130-160 beats/min), difficulty breathing (30-60 breaths/min), coughing, panting, dry feces with mucus and blood streaks, rapid transmission, and antibiotic treatment for pregnant sows has very little effect. After the sow's body temperature drops, abortion begins in 3-5 days, the symptoms of difficulty breathing ease somewhat, the rate of stillbirths and mummified fetuses reaches 20-25%, the incidence rate in postpartum piglets is high, and the survival rate is low.

Chronic infection: the pigs are in poor physical condition, with pale mucous membranes, jaundice, emaciation, coughing, and some abdominal breathing; estrus is delayed or mating repeatedly fails to result in conception. As the disease progresses, the limbs and ears of the pigs become cyanotic and appear blue-purple, starting from the ears and shoulders and gradually spreading until the whole body changes color. Lactating sows produce less milk or even no milk, accelerating piglet death, especially within 1 week after birth, when the mortality rate increases markedly, reaching 40-80%. If care is not strengthened, it can lead to worsening symptoms and death in sows.

2. Growing-finishing pigs

The clinical manifestations are mild flu-like symptoms, anorexia, depression, and anemia. After 4-5 days, mild jaundice appears, body temperature is above 41°C, and in the later stage there are coughing and panting, cyanosis of the limbs, and blue-purple patches on the back edges of both ears and on the tail. The incidence rate is about 10%, the mortality rate is about 50%, and the mortality rate is highest at 7-10 days.

3. Boars

The incidence rate is low (2%-10%), with anorexia. Breathing is accelerated, the course of disease is somewhat longer, some become paralyzed, the skin of the limbs and under the abdomen becomes cyanotic, the whole body is blue-purple, and there is local edema, especially obvious in the joints and flank areas. Sperm density is low and motility decreases. The mortality rate of adult boars is relatively low. Paralyzed pigs often develop secondary mixed infection with Streptococcus, and the condition worsens.

4. Piglets

The condition is often relatively severe. Newborn piglets have anemia, mild jaundice, fever, huddling, and diarrhea, and the mortality rate can reach as high as 85%. As the disease develops, the skin of piglets changes from pale to mildly yellow-stained, and in the later stage becomes blue-purple and cyanotic, especially obvious on the chest and abdomen. Difficulty breathing and coughing and panting are particularly prominent and obvious. Individual pigs have intense itching of the mouth and nose. In weaned piglets at 6 weeks of age, the proportion of stunted pigs is large and development is delayed.

Pathological Changes

The skin is pale, resembling wax yellow, and there is foam in the nostrils; the trachea and bronchi are filled with foam, the visible mucous membranes are pale, eyelid edema is common in piglets and growing pigs, there is yellow staining of varying degrees throughout the body, and subcutaneous edema. In stillborn fetuses, a large amount of clear fluid is present in the thoracic cavity; in piglets that died within 1 month, the edges of the anterior lung lobes generally have gray hepatized lesions; when the trachea is cut open, the interior is filled with foamy material; the hilar lymph nodes are enlarged, and the pulmonary interstitium is obviously widened; some pigs have exudative pneumonia or lobar pneumonia; the liver is enlarged and degenerated, brownish yellow, and the systemic lymph nodes are enlarged with hemorrhagic spots on the cut surface; the kidneys are pale and enlarged, with uneven gray-white necrotic foci on the surface, the spleen is enlarged and softened, and the colonic contents are thin; the renal capsule is easy to peel off, and there are pinhead-sized hemorrhagic points on the surface; piglets have subcutaneous edema, enlarged body surface lymph nodes, endocardial congestion, and hydropericardium and edema.

Prevention and Control Measures

Currently, there is no specific therapeutic drug for porcine reproductive and respiratory syndrome.

1. Because this disease often occurs secondary to swine fever, porcine contagious pleuropneumonia, swine pasteurellosis, porcine eperythrozoonosis, and other diseases, whether it is a single infection or a mixed infection, disinfection of pens, strengthening feeding, and reducing stress are important links. Control alone cannot achieve results. Only by combining prevention and treatment, strengthening feeding management, and frequently disinfecting the pens can it be effective. Once a pig farm is infected with PRRS, in addition to harmless disposal of stillborn fetuses and dead pigs and disinfection of the pens, the sick pigs should also be fed high-energy feed, multiple vitamins, and sufficient electrolytes; sows should be fed an appropriate amount of aspirin before farrowing. The following drug combination can be added to piglet feed, such as tiamulin 100 ppm + chlortetracycline 300 ppm + amoxicillin 150 ppm, used continuously for 15 days after weaning, which can solve most problems in nursery pigs and can prevent disease in pigs during the fattening period.

For treatment, Echinacea detoxification injection can be selected, 0.3 ml per 1 kg body weight, used continuously for 3-5 days; when treating sick pigs, antibiotics can be used to prevent secondary infection. At the same time, prescribing the right medicine according to different secondary infection symptoms has a certain effect on the recovery of sick pigs.

2. Vaccine prevention: it is recommended that 45 kg replacement gilts use attenuated vaccine; production sows are vaccinated with inactivated vaccine 6 days after farrowing and 60 days after mating; boars: first immunization 2-3 months before semen collection or mating, subcutaneously or intramuscularly 2 ml/head, and after an interval of 20 days, booster immunization with the same dose once, then immunized once every 6 months thereafter; piglets: at 21 days of age, injected subcutaneously or intramuscularly at 1 ml/head.