Porcine circovirus type 2 (PCV2) doesn’t look like the devastating ‘wasting’ disease of two decades ago that resulted in high mortality and failure to thrive. Instead, it manifests as a subtle, persistent drag on production today that leaves producers feeling like something is simply ‘off.’
New research confirms the PCV2d genotype is now ubiquitous across the U.S. industry, appearing in over 80% of clinical cases. By matching the vaccine to the dominant field strain, experts say producers can provide the most robust protection possible, effectively taking PCV2 ‘off the table’ so they can focus their resources on more complex challenges like porcine reproductive and respiratory syndrome (PRRS).
Why Modern Circovirus Doesn’t Look Like it Used To
The original PCV2 vaccines included protection against genotype “a” (the most common at the time) and “b.” What had become a major challenge for U.S. pig farmers was fading away because of the successful protection of these vaccines.
But something shifted, as viruses do. Veterinary diagnostic labs discovered less PCV2a and started finding more PCV2d.
“When they were finding PCV2d, they were not seeing the full-blown clinical signs like they saw before vaccines,” says Jana Morgan, DVM, senior key account veterinarian with Boehringer Ingelheim. “It led us to ask, what’s off? What do we need to look for? What more do we need to understand about PCV2d? We wanted to discover what PCV2d was doing to the system.”
To better understand how widespread this particular genotype was in the industry, Boehringer Ingelheim designed two studies. The first set out to determine if PCV2d was associated with particular flows or production systems from a geography perspective and system perspective. The other study sought to discover if PCV2d was actually leading to disease.
“We took two approaches to assess its distribution across the U.S. and swine-producing states,” explains Fernando Leite, DVM, associate director of technical marketing-swine at Boehringer Ingelheim. “We used oral fluids for simple detection and to see if genotype “d” was present or absent. We found that it was widely present in most swine producing states and across most of the production systems that we evaluated.”
In terms of the disease cases, the researchers followed strict criteria to validate that those pigs had clinical signs – lesions. Then, they sequenced the virus to see which genotypes were present.
“The ‘d’ genotype was present in more than 80% of the clinical cases that we investigated, and the ‘a’ genotype was present in around 15% of the cases that we investigated,” Leite says.
What Does This Mean for Vaccines?
Morgan points out there is cross protection between PCV2a and PCV2d. As the “d” genotype became more prevalent in production systems, the team worked to develop a “d” vaccine so they could have homologous protection.
“Although the ‘a’ is cross protecting, it is not doing exactly what we want it to do,” Morgan says. “We now have the ‘a’ and ‘d’ in the same bottle. It’s important to have that homologous protection to provide the most robust defense. I make sure producers understand that they will still have protection against ‘d’ if they only use the ‘a’ vaccine, but there is an economic impact by putting ‘d’ in there as well. Your production will be better, and you will decrease the clinical signs if you have ‘d’ in your system.”
When PRRS and PCV2d Mix
Recent research also indicates that PCV2d can be more virulent when combined with PRRS, Leite adds. That’s why it’s important to understand which genotype of circovirus is present on your farm.
“The more we understand, the more we can meaningfully intervene,” he says.
As PRRS also continues to evolve and become more frustrating for producers, Morgan says getting a handle on PCV2 helps.
“If we can take that piece off the table by putting a homologous vaccine in the pig that’s going to protect it to the best of its ability (whether it’s ‘a’ or ‘d’), we can start working harder to fight viruses like PRRS,” she says.
Do Diagnostics Align with a Shift in Data?
Producers are encouraged to look critically at small shifts in production numbers. If the “math is off,” diagnostics should be used to see if PCV2d is the underlying culprit, even in the absence of full-blown clinical symptoms.
“Understand what you’re seeing within your system,” Morgan says. “Yes, everyone looks at their closeout numbers. I think with PCV2d, the shift might be small. But if the diagnostics align with this small shift in production numbers, there are tools to shift that back.”
Questions about PCV2d being just in one flow or system in one area of the country have answers now, Leite says.
“PCV2d is really the predominant genotype in the industry today, across different production systems and states and locations,” he says. “Why not use the best tools that are available? If you want to optimize production, the tool is there. As always, work with your herd veterinarian to find the best strategy for your herd.”
