Porcine Reproductive and Respiratory Syndrome (PRRS), much to producers’ and veterinarians’ dismay, 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 like Mycoplasma hyopneumoniae and influenza, and makes pigs more susceptible to bacterial infections, like Streptococcus suis and Haemophilus parasuis.
The origins of a 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 that the piglet is born PRRS positive. Horizontal transmission happens when the pig acquires the infection directly, or indirectly, from other pigs: litter mates, pen mates, or any other pig in the area. PRRS can be spread by direct contact between naïve and infected pigs, aerosolization of the virus, and indirect contact via fomites (contaminated objects like boots, equipment, etc.). Once the piglet is infected, virus can be shed for weeks or even months.
Prevention of PRRS in finisher pigs needs to be multifaceted for best results. Starting with a PRRS negative pigs, implementing strict biosecurity, utilizing vaccines, and eradicating are all areas to focus on. Starting with a negative pig is incredibly important, which is why many farms have invested in filtering sow farms. This isn’t a perfect technology, but it has certainly reduced the occurrence of PRRS infections. We’ve all seen PRRS positive pigs start in the nursery, and should understand the value and benefit of having negative piglets.
Strict biosecurity should be enforced to ensure that people and equipment aren’t bringing PRRS onto your farm. Changing clothes, washing hands or wearing gloves, and changing boots between sites is important, as well as, thorough disinfection of equipment and facilities. 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 have the potential to reduce clinical signs. Vaccinated pigs infected with wild-type virus will typically 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.
There are several vaccines currently on the market such as: Ingelvac MLV PRRS and Ingelvac ATP PRRS, Fostera PRRS. Merck is also re-introducing PrimePac PRRS, and Elanco will soon be releasing their new PRRS vaccine: Prevacent PRRS. These are modified live vaccines, although killed autogenous and RNA particle vaccines are also available. Your choice of vaccine will be largely dependent 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 Pipestone veterinarian, to discuss a PRRS plan for your farm and assistance in making PRRS vaccination decision.
The final area of focus for producers to prevent PRRS outbreaks is to eradicate the virus from their sites. Multi-age sites are notorious for serving as a PRRS reservoir, ensuring that every group that passes through will become infected. Adjusting pig flow to ensure a complete depopulation, along with a thorough cleaning, then restocking with negative pigs should remove the virus from the farm. After restocking, switching to All-In/All-Out production will help eliminate the virus if subsequent PRRS breaks occur. Additionally, PRRS’ ability to persist in the environment also means that disinfection is incredibly important, especially between turns so that 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. Thankfully, there are tools in the producer’s toolbox to prevent or reduce the impact of a PRRS infection. Producers should focus on starting with PRRS negative pigs, implementing strict biosecurity to prevent spread between groups of pigs, vaccinating pigs if warranted, and eradicating PRRS from multi-age sites. 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.
Please contact your veterinarian or our swine specialist team with questions. Our swine specialist team can be reached at 507-562-PIGS (7447).
Brent Sexton, DVM, Pipestone Veterinary Services