Written by Brent Sexton, DVM, Pipestone Veterinary Service
Porcine reproductive and respiratory syndrome (PRRS) can have a devastating impact on pigs of all ages. In general, the introduction of a new strain of PRRS at any stage of pig production has the potential to cause severe damage. Not only can PRRS be devastating by itself, but it also exacerbates diseases such as Mycoplasma hyopneumoniae and influenza, and makes pigs more susceptible to bacterial infections, such as Streptococcus suis and Haemophilus parasuis.
The origins of PRRS infections can be thought of in two categories: vertical or horizontal transmission. Vertical transmission occurs when PRRS is passed from the sow to the piglet during gestation. The virus infects the sow, then crosses the placenta and infects the piglet so the piglet is born PRRS-positive.
Horizontal transmission happens when the pig acquires the infection directly, or indirectly, from other pigs: littermates, pen mates or other pigs in the area. PRRS can be spread by direct contact between naïve and infected pigs, aerosol movement of the virus, and indirect contact via fomites (contaminated objects like boots, equipment, etc.). Once the piglet is infected, the virus can be shed for weeks or even months.
A multifaceted approach is key to PRRS prevention. Starting with PRRS-negative pigs, implementing strict biosecurity, vaccines, and eradication are all areas of focus. Beginning with a negative pig is important, which is why many farms have invested in filtered sow farms. This isn’t perfect, but it has reduced the occurrence of PRRS. We’ve all seen PRRS-positive pigs in the nursery, and should understand the value of having negative piglets.
Strict biosecurity should be enforced to ensure people and equipment aren’t bringing PRRS onto your farm. Additionally, if you have multiple groups of pigs on the same site or within the same barn, it is crucial to minimize the amount of contact these pigs have, both directly with each other, and indirectly via dirty boots, coveralls or other equipment. Vaccinating market hogs against PRRS is a common practice within the industry. Vaccines do not prevent infection, but they do have the potential to reduce clinical signs. Vaccinated pigs infected with wild-type virus typically will have better rates of gain, lower mortality rates and a higher proportion of full-value market pigs. Vaccination can also significantly reduce the amount of virus that is shed by infected pigs. Unfortunately, the efficacy of vaccination can vary widely depending on the strain of PRRS. As an RNA virus, PRRS can mutate rapidly, making it difficult for a product to offer protection from multiple strains.
Your choice of vaccine will largely depend on your individual needs, PRRS status of the sow farm, ability to vaccinate at certain stages of production and exposure risk. With the help of your veterinarian, discuss a PRRS plan for your farm.
Multi-age sites are notorious for serving as a PRRS reservoir, ensuring every group that passes through will become infected. Adjusting pig flow for a complete depopulation, along with a thorough cleaning and restocking with negative pigs, should remove the virus from the farm. At this point, switching to all-in/all-out production will help eliminate the virus if subsequent PRRS breaks occur. Additionally, the virus’ ability to persist in the environment means disinfection is very important, especially between turns so the virus from a previous group doesn’t infect a new group of pigs. There is no doubt about it, PRRS is a frustrating and difficult disease to deal with. Regardless of the age of pig, a substantial economic impact can be expected when infection occurs. Although nothing will guarantee the prevention of PRRS, producers can take steps to reduce the disease’s impact, as well as improve pig health and their bottom line.
Brent Sexton, DVM, grew up on a farm near Rockwell City, Iowa. He was active in both 4-H and FFA, and credits his desire to become a veterinarian to that experience. Sexton attended Iowa State University, where he completed his animal science degree and his degree in veterinary medicine. His primary interests are infectious swine diseases, diagnostics interpretation and swine production. He joined Pipestone in May of 2018.