Time to Start Talking about PRRS Eradication

Veterinary panel agrees that any swine disease cleanup program must be producer-driven in order to achieve any measure of success. Three leading swine veterinarians agree it's premature to start an eradication program to deal with porcine reproductive and respiratory syndrome (PRRS). I don't think we are ready for it, stresses Matt Anderson, DVM, Suidae Animal Health and Production of Algona, IA.

Veterinary panel agrees that any swine disease cleanup program must be producer-driven in order to achieve any measure of success.

Three leading swine veterinarians agree — it's premature to start an eradication program to deal with porcine reproductive and respiratory syndrome (PRRS).

“I don't think we are ready for it,” stresses Matt Anderson, DVM, Suidae Animal Health and Production of Algona, IA. “If we were voting on an eradication procedure today, I would vote against it. But I think we need to start talking about it — and it's possible we could be talking about it for three or four more years.”

Long-term, eradication of PRRS should be our goal, but there are a lot of steps along the way that need to be taken first, adds Keith Aljets, DVM, Veterinary Medical Center in Williamsburg, IA.

“I am in agreement with my colleagues,” adds Hans Rotto, DVM, Iowa State University (ISU) diagnostician, who previously served as a swine veterinarian with Christensen Family Farms in Sleepy Eye, MN.

The three swine veterinarians participated in an open-ended question-and-answer session on PRRS with producers at an Iowa Pork Congress seminar moderated by ISU swine veterinarian Locke Karriker.

Following are a few of the exchanges:

Serum therapy: The use of serum therapy or inoculation was a key question.

Anderson says his experience with the process has been quite good. He adds, “I think it is absolutely important that we get a naïve animal to start with, no matter where that animal comes from, and immunize it against the strain or strains that are present on your farm.”

Anderson's preferred way to use serum therapy is in early exposure to naïve gilts, providing them plenty of time to cease shedding the virus prior to entry into the sow herd.

Rotto says PRRS virus has a history of not being very efficient at infecting a herd. “We talk about farm-to-farm spread, yet we may have pockets in our breeding and gestating sows that have not yet been exposed to the virus. That's where we can use serum therapy — to help acclimate our gilts with the long-term goal of stabilizing the immunity of our sow herd.”

Aljets says that his experiences with a control plan utilizing serum therapy are similar to those he's had with the use of commercial PRRS vaccine and other control methods.

“Sometimes they work really well and sometimes they don't work at all,” he says. And he reminds that PRRS vaccine should be used in a similar fashion as serum.

If you are going to use vaccine, you need to be committed to its use and vaccinate entire populations of animals, not just a group or two of replacement gilts, notes Karriker.

None of the trio indicated they had experienced any disasters with the use of serum inoculation. But Aljets adds a note of caution for those using the process.

“The real question I have with serum injection is not when to start serum. I think the decision to isolate PRRS virus infecting a sow farm and inoculate replacement gilts is a valid one. The question I have is, when does the use of serum therapy end? This year you may have one strain infect your herd, and next year it could be another one. Do you drop one strain of the PRRS virus therapy because you haven't seen it for a few years?” he questions.

Before beginning serum therapy, you and your veterinarian need to consider when and how you will end the serum therapy procedure, adds Karriker.

Anderson agrees, and suggests that once a sow herd enters an “era of stability and we become confident that sow herd is no longer shedding virus to the pigs, and we have no herd cyclicity on the site, that's when we can begin to start thinking about stopping that injection program.”

Aljets also warns that if producers plan to inoculate their sow herds with PRRS virus, they need to make sure it is done with a resident virus found on the sow farm and not a PRRS virus that was just introduced into the sow herd. Serum therapy, if not done correctly, has the risk of introducing a new PRRS strain into the sow herd.

Anderson says Aljet's point cannot be overemphasized. “You need to know that the virus you are using to inoculate your sows is the one that is causing problems. When you hear about these strategies that have not been successful, sometimes I think there is a difference in the virus used for inoculation and the virus that caused the initial assault,” he surmises.

All three veterinarians agree that 8-12 weeks after serum inoculation, producers should start to see healthier pigs if proper farrowing protocols are followed that don't propagate PRRS virus in the farrowing barns.

“How you move pigs, handle fallbacks and crossfoster pigs will have an affect on whether you will wean PRRS-negative pigs,” comments Aljets. The more litters that are left intact, the shorter period of time you risk propagating the PRRS virus infection amongst the pigs in your farrowing barns, and the less problems there will be from PRRS serum therapy, he notes.

Anderson says by limiting the use of serum therapy to gilts, offspring seem to have more of a chance to thrive.

Above all, while serum therapy is a tool that can help control the PRRS virus, it is not without risks, stresses Aljets. “If you plan to use serum therapy, you need to discuss and understand those risks with your veterinarian.”

Injectable vaccinations: Because needles can increase the risk of spreading PRRS postweaning amongst nursery penmates, Anderson suggests producers consider switching to oral vaccinations and antibiotics for the control of secondary diseases like salmonella, ileitis and mycoplasma.

PRRS-mycoplasma organisms are well-known to work together to cause major financial problems to hog operations, Anderson continues. So producers may well need to vaccinate 2-4 weeks ahead of expected seroconversion to protect their herd from mycoplasma. An option would be to strategically use a number of antibiotic options if PRRS-mycoplasma infection appears to be breaking through vaccine protection.

Area spread and aerosol spread: Karriker says he receives lots of calls and hears much confusion about these two terms.

Area spread refers to the means — pigs, people, trailers, etc. — in which the PRRS virus moves from farm to farm.

Aerosol spread refers specifically to the ability of the virus to move by itself in the air or with wind currents from site to site.

Karriker's opinion is that aerosol spread occurs very, very rarely.

In contrast, area spread is a very common event that appears to be the result of several combined factors. He stresses producers should focus on what they can control and shore up biosecurity measures to slow area spread.

Biosecurity: “I think we have all underestimated the value of biosecurity, and I am not just talking about things like shower-in and shower-out, but things to protect the herd, like trailers and transport,” emphasizes Rotto.

Science shows that you cannot simply wash PRRS out of a vehicle, says Anderson. “We are talking about something that is a whole lot smaller than your average bacteria. Viruses are able to hide and survive in a moist environment for long periods of time.”

The panel agrees that proper washing, disinfecting and drying are necessary to rid trailers and trucks of the PRRS virus.

If producers are dealing with naïve pig populations, they should consider dedicating a trailer to that segment of production, says Rotto.

He also suggests producers should not let down their guard when it comes to biosecurity.

“Remember that most farms are naïve to another set of PRRS viruses, and sometimes a one-time capital investment in biosecurity can protect you, not just from PRRS, but from almost all other bugs.”

Above all, keep biosecurity simple and practical, and protect the sow source. Make sure gilts and semen are negative for PRRS, Rotto emphasizes.