Pig reproductive-respiratory syndrome and its modern control strategy

Infectious diseases have been a problem of farming society and humanity since time immemorial. Diseases covered large areas, decimated animal populations, and caused large economic losses. Many of them have been defeated or brought under control, but new diseases such as porcine reproductive-respiratory syndrome, circovirus, and others have emerged in the swine industry.
Porcine reproductive-respiratory syndrome (PRRS) is a viral disease caused by an RNA virus belonging to the Arteriviriidae family and the Arterivirus genus. Porcine reproductive-respiratory syndrome or as it is also called blue ear disease and infertility syndrome. As the name implies, it is characterized by disorders of the respiratory system and reproductive system, namely: abortion, mummified fetus, premature birth, birth of weakened and dead piglets, damage to the respiratory organs, and also blue, bluish-reddish coloration in the area of the ears, on the vulva.
Reproductive and respiratory problems were first reported in 1987 in the United States. There are two genotypes: 1. European - widespread Lelystad virus; 2. USA - widespread VR-2332 virus. The disease is important from an economic point of view because it causes huge losses in the pig industry every year. Foreign statistics are unequivocal and indicate serious economic losses. Production losses due to the disease in 2012-2013 in the USA were 664 million USD (American Swine Veterinarians Association 2013), in Europe (Netherlands, Spain, Denmark, Switzerland) about 126 million euros.
source of spread of infection: 56% - sick pig; 20% - infected stall; 21% - through indirect distribution (cars, devices, clothes, shoes and others); 3% - wild ducks and possibly other birds.

The virus has many ways of transmission and is very persistent in the environment. Adult pigs spread the virus much faster than young animals. Direct animal-to-animal contact is the most dangerous. Transmitted by sperm through artificial insemination, excreted in milk and urine. Scientists also assume that the virus can spread up to 3 km by airborne droplets. The pig remains a carrier of the virus for 2-3 months. In some cases, it is believed that this condition may last longer. Duration of stay of the virus in the blood is up to 56 days, in sperm - up to 92 days.

Porcine reproductive-respiratory syndrome has a special relationship with macrophages, especially lung macrophages (alveolar macrophages). Macrophages are part of the immune system and have a protective function, they absorb viruses and bacteria that invade the body. In alveolar macrophages, the pathogen reproduces, that is, the virus multiplies inside the macrophage and destroys them. As a result, up to 40% of macrophages are destroyed, which significantly weakens the body's protective functions and general immunity. As a result, we get a weakened body that is easily susceptible to various diseases. During the disease, the virus can support the development of side pathogens, which can lead to a more serious course of the disease.
This is an intrauterine infection, during which the virus is transmitted to the fetus through the placenta. The exact spreading period has not been confirmed, but it usually happens from 60-70 days of Maceobi.
Clinical signs are variable and depend on the specific virulence of the virus strain. The disease manifests itself in the form of enzootic disease, it is most pronounced during childbirth. The incubation period is from 4 to 35 days. In sows, the disease begins with temporary refusal of food, lethargy, temperature increase, during abortion the temperature reaches 41.5 degrees. Some pigs show symptoms of respiratory tract damage, bluish-reddish coloration in the area of the ears, on the vulva (blue). In piglets, the disease is characterized by abortion, mummified fetuses, premature births, birth of weakened and dead piglets. Abortions can be up to 50%. Weak and non-viable piglets are characterized by respiratory disorders with cough and pneumonia, muscle weakness, conjunctivitis, weight gain can be reduced to 50-70%.

At the autopsy of aborted and stillborn piglets, bruises, swelling of subcutaneous tissues, increased exudate in the chest cavity, liver dystrophy, and signs of pneumonia are observed.
The diagnosis is established on the basis of epizootic data, clinical signs and the results of laboratory tests. For diagnosis in the laboratory, in order to detect the disease-causing virus, antigen, genome, the most appropriate samples are brain, lung, chest tissues, as well as blood samples taken from several pigs at the same time.
In order to consider a stall as suspicious for porcine reproductive-respiratory syndrome, the following factors should be taken into account and criteria: 

a) Abortion or premature birth is more than 8% b) Dead piglets or mummified fetus is more than 20% c) Mortality of piglets in the first week of life is more than 25%. If two of these criteria are satisfied, then the stall can be considered suspicious for this virus.
Pig reproductive-respiratory syndrome is a problematic disease for pig farmers considering the following aspects: 1) phylogenetic diversity of the causative agent and emergence of new highly pathogenic strains; 2) Absence of standardized disease control and monitoring programs, protocols.
Preventive immunization of animals is considered to be the greatest and most effective veterinary measure of all time. The effectiveness of the vaccine is evaluated based on statistical analysis. In the last decade, significant results have been achieved against porcine reproductive-respiratory syndrome and effective remedies have been proposed. "Inveti" company offers highly effective anti-virus vaccine "PROGRESSIS" for immunization of pigs, produced in France by "CEVA" company, which is successfully used by pig farms operating in Georgia.

Gurami Melkadze
"Invet" company
Academic doctor.