PRRS is a problem — that’s not news to any producer or veterinarian in the industry. However,new information continues to emerge, and the latest from Iowa State University (ISU) offers some interesting, though daunting, metrics on how many strains and variants even a single farm could be facing.
As further developments in monitoring and reporting strategies continue to evolve, so does the picture of PRRS. I caught up with Dr. Daniel Linhares and Dr. Giovani Trevisan of ISU to discuss their recent study findings completed with Dr. Gustavo Silva.
A Diverse Cloud
A facet of their study included completing whole PRRSv genome sequencing on farms experiencing an outbreak to examine what those farms were up against. Surprisingly, they found that 90% of the farms they sampled were facing multiple PRRSv strains simultaneously, with some showing evidence of four or more strains.
The initial reaction is to jump — that is expected. If you are using a modified live virus (MLV) vaccine and experience a break, you would expect multiple strains to be present. Dr. Trevisan explained that was not always the situation though. “We had cases where naive breeding herds went through a PRRS break, used live virus inoculation, and we found more than two PRRS viruses after the break,” Trevisan says. The co-infections were more diverse than expected and often showed recombination between wild-type and vaccine viruses.
The research team describes this occurrence as a diverse “cloud” of PRRSv co-circulating and ever-evolving. “There is no such thing as ‘the’ virus — or one homologous virus circulating. It is expected that anyone dealing with PRRS is dealing with a family of PRRS, sometimes very related and sometimes not at all,” added Dr. Linhares.
You Only Know What You Know
And you don’t know what you don’t. The clarity, or lack thereof, found in this research brings to light the necessity of monitoring and testing. This can be accomplished through:
• Active Surveillance: samples collected no matter the clinical signs, or even without evidence of disease
• Passive Surveillance: reactive testing due to a clinical sign in the herd
Does this mean all producers should be doing some kind of ongoing testing? Not necessarily, but there are cases where a more active approach is warranted. Breeding stock is an absolute.
If you are a multiplication farm, there is immense value in doing active surveillance. Otherwise, it depends on your risk factors and future implications.
For example, are you going to commingle animals downstream? You may want to consider active surveillance because you are putting not just the downstream flow of this barn at risk, but also the flow of other farms.
At the sow farm, processing fluids are a practical sample to screen for PRRSv and can be collected during a process that is already in place—castration. Beyond that age, you should look to family oral fluids or serum collection for continued surveillance.
If you are a single-site with no other animals coming in and no PRRS clinical signs, then it’s certainly reasonable to not have ongoing surveillance.
In the Case of a Break
As summarized by Dr. Linhares and Dr. Trevisan, it’s rarely a single, clear-cut variant that you are facing. Therefore, our recommendation is that anybody with a breed-to-wean farm going through a PRRS outbreak should probably have whole genome sequencing completed. By even retaining samples, we can sequence if and when necessary for follow-up questions, or unexpected results.
Serum tends to be your gold standard sample to achieve results, especially in cases of PRRSv with low cycle threshold (CT) values. Another useful test is lung tissue sampling, or a newer approach is using tongue-tip fluids from dead pigs. RNA detection in tongue tips has similar sensitivity to that of process fluids, serum and family oral fluids. The ISU researchers report that this method is “handy when there is an unexpected drop in CT values of polymerase chain reaction (PCR) results from processing fluids, serum of family oral fluid samples and also, when there is an atypical long duration of PCR positive results.” This approach on stillborns can help you determine if the infection originated with the breeding herd (vertical transmission) or the farrowing house (horizontal transmission).
“Each sampling approach serves to address a specific question. For example, processing fluids are great for screening whole-herd viral activity. Family oral fluids are to verify the PRRSv activity in the weaning-age pigs, serum is ideal for completing whole genome sequencing and tongue tips are for assessing vertical transmission,” summarizes Dr. Linhares.
Seeing Through the ‘Cloudiness’
Big picture: Multiple viruses will have greater impact than individual viruses, and testing provides information to inform decisions. Sometimes results can be uncomfortable, but as Dr. Linhares’ challenges, “You can’t manage what you don’t monitor. Don’t wait until your productivity doesn’t bounce back in the expected recovery time to start asking questions.”
PRRS is a tough and nimble nemesis, and the only way to manage is to have as much information as possible.
Clayton Johnson, DVM, is one of the swine health experts at Carthage Veterinary Service who rely on science and experience to provide unique and practical solutions to achieve the best outcomes for producers and their animals.
