Symptoms and Prevention and Treatment Methods of Porcine Reproductive and Respiratory Syndrome

Porcine reproductive and respiratory syndrome was once called mystery swine disease, new swine disease, porcine epidemic abortion and respiratory syndrome, porcine reproductive and respiratory syndrome, blue ear disease, swine plague, etc. It is a syndrome of reproductive and respiratory disorders in pigs caused by a virus. Its rapid spread, wide scope of involvement, and such high morbidity and mortality rates are unprecedented. Let us take a look below at the symptoms and treatment of porcine reproductive and respiratory syndrome.

Acute form

Affected sows mainly show depression, reduced or absent appetite, fever, and varying degrees of respiratory difficulty. In late gestation (105 to 107 days), sows experience abortion, premature birth, stillbirth, mummified fetuses, and weak piglets. The abortion rate of sows can reach 50% to 70%, the stillbirth rate can reach more than 35%, and mummification can reach 25%. Some newborn piglets show symptoms such as respiratory difficulty, incoordination, and mild paralysis, and the mortality rate increases significantly within 1 week after birth (40% to 80%). A small number of sows show postpartum agalactia, retained placenta, and increased vaginal discharge.

One-month-old piglets show typical respiratory symptoms, respiratory difficulty, sometimes abdominal breathing, reduced or absent appetite, body temperature rising above 40 degC, and diarrhea. The hair coat is rough and disheveled, with incoordination, progressive emaciation, and eyelid edema. A small number of piglets may show purpling of the ears and body surface skin. The mortality rate of pre-weaning piglets can reach 80% to 100%. After weaning, the weight gain of piglets decreases, daily weight gain can decline by 50% to 75%, and the mortality rate rises (10% to 25%). Surviving pigs grow slowly and are prone to secondary infections.

Growing pigs and finishing pigs show mild clinical symptoms, with varying degrees of respiratory symptoms. A small number of cases may show coughing and dark purple coloration on the back of both ears, the edges, the abdomen, and the tail skin. Infected pigs are prone to secondary infections and show corresponding symptoms.

The incidence rate in breeding boars is relatively low, mainly showing general clinical symptoms, but the semen quality of boars declines, sperm abnormalities appear, and semen can carry the virus.

Chronic form

This is currently the main form of PRRS in large-scale pig farms. It mainly manifests as decreased production performance of the herd, slow growth, decreased reproductive performance of the sow herd, decreased immune function of the herd, and susceptibility to secondary infections with other bacterial and viral diseases. The incidence of respiratory diseases in the herd (such as mycoplasma infection, infectious pleuropneumonia, streptococcosis, and eperythrozoonosis) rises.

Subclinical form

Infected pigs do not become ill and show persistent infection with PRRSV. The serological antibodies of the herd are positive, and the positive rate is generally 10% to 88%.

Prevention and control measures

After infection with porcine reproductive and respiratory syndrome, there is currently no specific therapy. Most measures are aimed at alleviating acute symptoms, preventing secondary infections, and reducing losses.

(1) In the first month of the outbreak, drugs such as aspirin can be used to treat late-gestation sows to reduce fever and prolong gestation. At the same time, antibiotics are used to treat sows to prevent secondary infections.

(2) When feed intake of the herd declines, high-energy feed should be provided.

(3) During the acute phase of the outbreak, multiparous sows should have mating postponed, but more replacement gilts should be mated to reduce the decline in productivity. When boars are affected and semen quality declines, artificial insemination should be strengthened.

(4) Ensure that weak newborn piglets receive colostrum in time, and iron supplementation and tail docking should be postponed; give newborn piglets prophylactic antibiotics to prevent diarrhea; fostering is prohibited to avoid cross-contamination.

(5) Strengthen prevention of diseases in the herd such as pleuropneumonia, pseudorabies, streptococcosis, and enzootic pneumonia to increase the disease resistance of pigs.

(6) Add antibiotics to prevent secondary infections in growing pigs, and supplement an appropriate amount of vitamin E and the trace element selenium.

(7) Maintain good hygiene conditions, strengthen environmental disinfection, and clean farrowing crates promptly.

(8) Maintain a strict "all-in, all-out system," empty pens promptly and carry out fumigation disinfection to interrupt the cycle of the virus in the pig production process; and carry out early segregated weaning to prevent transmission caused by mixed rearing.

(9) Strengthen the management of replacement gilts. For newly introduced replacement pigs, mating should be postponed so that natural adaptation can form.

(10) For PRRS-positive pig farms, lyophilized PRRS vaccine can be used to immunize replacement gilts once before mating, with a second immunization 21 days later. Sows that produced stillbirths due to porcine reproductive and respiratory syndrome may not need vaccination within half a year. Multiparous sows can be inoculated with 1 dose 21 days after farrowing, and piglets (7 to 21 days of age) can be inoculated with half a dose. Boars are not inoculated (for severely contaminated farms, sows may be inoculated once with inactivated PRRS vaccine in the middle and late stages of gestation). For PRRS-negative pig farms, inactivated PRRS vaccine can be used to immunize replacement gilts once before mating, with a second immunization 21 days later. Multiparous sows are inoculated during the non-pregnant period, and boars and piglets do not need to be inoculated.