Porcine Reproductive and Respiratory Syndrome (PRRS) in Pigs

Porcine Reproductive and Respiratory Syndrome, or PRRS, is a viral disease caused by PRRS virus (PRRSV). It affects pigs of different ages in different ways. In breeding herds, it is best known for reproductive problems such as abortions, stillbirths, mummified fetuses, premature farrowing, and weak-born piglets. In young and growing pigs, it more often shows up as respiratory disease, poor growth, and higher death loss.

PRRS matters because it does more than cause one set of symptoms. The virus targets cells involved in the pig's immune response, especially macrophages, which can make affected pigs more vulnerable to other infections. That is one reason PRRS often becomes part of a larger respiratory disease picture on farms.

For pet pigs and small herds, PRRS can still be serious even though it is discussed most often in production medicine. If your pig has breathing changes, fever, poor appetite, or if a breeding pig has pregnancy losses, your vet may consider PRRS along with other infectious causes. Early veterinary involvement helps protect both the sick pig and other pigs on the property.

PRRS is caused by porcine reproductive and respiratory syndrome virus (PRRSV), an arterivirus. The main source of infection is an infected pig. The virus can spread through direct pig-to-pig contact, movement of infected animals, and contaminated semen. It can also move indirectly on equipment, clothing, boots, vehicles, and other farm traffic when biosecurity breaks down.

In breeding herds, PRRS is especially important because the virus can cross the placenta late in gestation, leading to stillbirths, weak piglets, and abortions. In young pigs, the virus damages immune defenses and the lungs, which can set the stage for more severe disease when other pathogens are present.

Risk goes up when new pigs are introduced without quarantine, when groups of pigs mix frequently, or when sanitation and traffic control are inconsistent. Your vet may also look at nearby pig density, semen source, transport practices, and herd vaccination history when assessing how PRRS may have entered or spread through a herd.

Your vet diagnoses PRRS by combining clinical signs, herd history, and laboratory testing. Signs like abortions, weak-born piglets, thumping respirations, and postweaning respiratory disease can raise suspicion, but they are not specific enough to confirm PRRS on their own.

Common tests include PCR to detect viral genetic material and ELISA to look for antibodies showing exposure. In some cases, your vet may recommend virus sequencing to compare strains and help track where infection may have come from. For reproductive cases, samples from multiple affected fetuses may be needed because not every fetus in a litter is infected.

Modern herd monitoring often uses population-based samples such as oral fluids, processing fluids, postmortem tongue fluids, or pooled fetal thoracic fluids. These approaches can be practical and cost-conscious for larger groups. Your vet will decide which sample type makes the most sense based on whether the concern is an individual pig, a litter, or a whole-herd outbreak.

Prevention focuses on biosecurity first. Keep new pigs separated before introducing them to resident pigs, control visitor and vehicle traffic, use dedicated boots and equipment, and clean and disinfect items that move between groups. Semen source, transport practices, and contact with other pigs all matter. For any new arrival, your vet may recommend quarantine and testing before mixing.

Vaccination may be part of prevention, but it is not a one-size-fits-all answer. Modified-live and inactivated products are used in some settings, and your vet can help decide whether vaccination fits your herd's risk level, breeding goals, and current health status. A vaccine plan works best when paired with strong management rather than used alone.

Ongoing monitoring is also important. Herd-level testing with oral fluids, processing fluids, or other pooled samples can help detect circulation early and track whether control steps are working. If you keep pigs at home, avoid sharing equipment with other pig properties, limit exposure at shows or events, and contact your vet quickly if you notice reproductive losses or respiratory disease.