How to prevent and treat highly pathogenic porcine reproductive and respiratory syndrome (PRRS)? A detailed explanation of the technical key points

This disease is a severe viral disease of pigs that has emerged in recent years, an acute highly lethal epidemic disease caused by a variant strain of porcine reproductive and respiratory syndrome virus. The virus is extremely contagious. In infected pig farms, the morbidity rate of piglets can reach 100%, the mortality rate can reach more than 50%, and the abortion rate of sows can reach more than 30%. It is also characteristic that growing-finishing pigs can develop the disease and die.

1. Pathogen:

The pathogen of this disease is porcine reproductive and respiratory syndrome virus, caused by Lelystad virus.

2. Epidemiology:

Pigs of all ages and types can be infected, but pregnant sows and piglets within one month of age are the most susceptible. The incubation period is 2-4 days for piglets and 4-7 days for pregnant sows. The main route of infection is the respiratory tract. Airborne transmission, contact transmission and vertical transmission are the main modes of transmission. Sick pigs, virus-carrying pigs, piglets born to diseased sows, and contaminated environmental equipment are sources of infection. Rats may be carriers and transmitters of the pathogen. This disease spreads more easily among piglets than among adult pigs.

3. Clinical symptoms:

This disease is mainly characterized by reproductive disorders in sows and respiratory symptoms in piglets.

Sows: listlessness, poor appetite, temporarily elevated body temperature, coughing, varying degrees of difficulty breathing, abnormal estrus or infertility. Pregnant sows may farrow prematurely or give birth to stillborn fetuses, mummified fetuses and weak diseased piglets. The abortion rate can reach more than 30%. Some have no milk after farrowing and retained placenta. A small number of sows have transient bluish-purple or blue-purple patches on both ears, the ventral sides and the skin of the vulva.

Suckling piglets: body temperature can reach above 41°C, difficulty breathing, sometimes abdominal breathing, anorexia, diarrhea, red ears, conjunctivitis, rough hair coat, ataxia, prone to secondary infection by other diseases. The morbidity rate can reach 100%, and the mortality rate can reach 50%. Piglets that survive are chronically emaciated and grow slowly. Growing-finishing pigs: show mild flu-like symptoms, temporary anorexia and mild difficulty breathing. A small number of pigs cough and have transient dark bluish-purple patches on the back and edges of both ears and on the skin of the tail.

Boars: the morbidity rate is low, about 2-10%, showing anorexia, difficulty breathing and emaciation. A very small number of boars have skin discoloration on both ears. Semen quality of boars declines. In addition, because the pathogen of this disease has obvious variability, the clinical manifestations of this disease are very complex and can often be divided into acute, subclinical and chronic types. Moreover, the symptoms during the disease period differ among different countries, and different strains as well as management factors can all affect the appearance of clinical symptoms and production losses.

4. Pathological autopsy changes:

In stillborn fetuses and weak piglets, a large amount of clear fluid can be seen in the thoracic cavity. The lungs of suckling piglets have areas of hepatization, the colonic contents are not thin, and edema occurs in the mesenteric lymph nodes, subcutis and muscles. Boars, sows and finishing pigs have no grossly visible changes. On autopsy: infarction foci can be seen at the edges or surface of the spleen, the kidneys are clay-yellow, and petechial spots ranging from needle-tip to millet-grain size can be seen on the surface. Hemorrhagic spots and hemorrhagic patches can be seen in the subcutis, tonsils, heart, bladder, liver and intestinal tract. In some cases, gastrointestinal bleeding, ulcers and necrosis can be seen.

5. Diagnosis:

This disease is very difficult to diagnose based only on symptoms and epidemiology, and laboratory diagnosis is needed for confirmation. Whether the disease is present can be judged according to the following conditions: the rates of premature farrowing, abortion, stillbirth and weak piglets in sows increase markedly, and the number of sows with no milk after farrowing increases; respiratory symptoms increase in piglets within one month of age, some piglets have red ears, diarrhea increases, the number of emaciated piglets increases, the cure rate declines, the weight gain rate declines, and the mortality rate increases markedly; the whole herd of pigs has recently had cold-like symptoms, and some pigs have bluish-purple or blue-purple patches on both ears, under the abdomen, on the perineum and on the skin of the tail.

6. Prevention and treatment:

Comprehensive epidemic prevention measures and vaccine immunization are effective ways to control and reduce the incidence of PRRS.

First, quarantine must be strengthened. When introducing breeding stock and purchasing piglets, a strict isolated rearing system must be implemented to prevent the virus from being brought in from epidemic areas;

Second, self-breeding and self-rearing should be advocated, closed housing management should be implemented, isolation and disinfection systems should be strictly enforced, farrowing house isolation should be implemented, suckling piglets should be weaned as early as possible, and disease-free clean pig farms should be established;

Fourth, an "all-in, all-out" system should be adopted for growing-finishing pigs, and the pig house should be thoroughly disinfected after the pigs are sent to market;

Fifth, vaccines should be used correctly. Attention should be paid to distinguishing the different usage characteristics of attenuated live vaccines and inactivated vaccines. When vaccinating pigs on disease-free farms, inactivated vaccines should be chosen, while when vaccinating pigs that have already contracted PRRS, attenuated vaccines must be chosen. A reasonable immunization program should be formulated according to local conditions to prevent immunosuppression.

Porcine reproductive and respiratory syndrome often causes secondary diseases such as swine fever, porcine contagious pleuropneumonia and swine pasteurellosis. Therefore, once a pig farm is infected with PRRS, in addition to harmless treatment of stillborn fetuses and dead pigs and cleaning and disinfecting the pig house, sick pigs should also be fed high-energy feed, vitamins and sufficient electrolytes. Sows should be given aspirin mixed into the feed before farrowing. When treating sick pigs, antibiotics should be used to prevent secondary infection, and at the same time, symptomatic treatment should be given according to different secondary infection symptoms.