Three short years ago, the pork industry saw porcine circovirus-associated disease (PCVAD) burst on the scene, causing dramatic losses.

Since that time, Carthage Veterinary Service (CVS), Ltd., Carthage, IL, has conducted numerous research trials on the disease syndrome and vaccines to control it.

CVS veterinarian Joe Connor says that all of the commercially available vaccines continue to provide excellent results and those products have proven effective around the world.

“A high percentage of our pigs are vaccinated and we've got good, efficacious vaccines and good vaccine availability,” he reported at a Fort Dodge Animal Health seminar at World Pork Expo. Problems that do occur relate to improper vaccine timing or pigs missed during vaccination.

When missed during vaccination, clinical signs can occur in individual pigs, characterized by pneumonia or brown-red-black diarrhea associated with porcine circovirus type 2 (PCV2) that is often seen as a precursor to PCV2-associated postweaning multisystemic wasting syndrome (PMWS). Lymph nodes become enlarged. Jaundice and wasting are characteristics of PMWS; 6-10% of recent PCV2 infections studied have presented a parvovirus co-infection, Connor says.

Questions Remain

While vaccination affords solid protection against circovirus, Connor says several key questions remain:

The first question involves the role of PCV2 in reproduction. “We have been tracking a low number of cases of reproductive failure primarily seen as increased abortions, increased mummies and an increase in low-viability pigs in several herds,” he explains. To date, the only infectious agent identified has been PCV2, and he's confident that PCV2 is the primary component.

In cases of reproductive failure and an increase in preweaning mortality, those sow herds have been subsequently vaccinated for circovirus.

A second question relates to the role of viremia (infection in the bloodstream) in the context of a circovirus infection. In seven CVS studies to date that looked at PCV2 viremia, 2.5% of pigs were shown to be viremic on placement at 18 to 21 days of age. Control group pigs (unvaccinated) in the studies consistently became infected from one of three sources: the sow, other pigs or from the environment. Because circovirus is quite stable in the environment, rigorous washing, disinfecting and drying during the trials did not eliminate the virus from hog facilities nor from hog transportation systems, he notes.

Control group pigs reached the height of being viremic at 8 to 12 weeks of age, while vaccine counterparts typically peaked for viremia at 12 weeks of age, but at virus levels several times lower than control pigs. Pigs vaccinated with Fort Dodge's Suvaxyn's circovirus vaccines recorded very low levels of viremia.

Connor says viremia may be important when pig flows in pig-dense areas have co-infections with porcine reproductive and respiratory syndrome (PRRS), Mycoplasmal pneumonia or swine influenza virus (SIV).

Whether or not viremia produces performance issues, a very high percentage of control group pigs in circovirus vaccine trials turn up positive.

“We can use that information to say that even given today's economy, we have to keep these PCV2 vaccines in the pig flows based on their effectiveness in all of our studies,” Connor emphasizes.

A third issue is the role or interference of maternal antibody or immunity in the timing of piglet vaccination. Connor says each farm must evaluate the impact of virus activity within the sow herd and the role of parity to decide whether vaccine timing is appropriate to the age of the pig.

The key drivers for setting up a vaccination program are the impact of maternal antibodies and other disease agents that might be present and transmitted prior to pigs developing protective immunity for PCV2.

The PRRS virus presents the biggest challenge. “If we delay vaccination for PCV2 until pigs are 5 weeks of age, and we recognize that it takes 30 days to build excellent immunity, then a lot of those pigs have already been infected with PRRS, so we need to pull our age of vaccination down to weaning,” Connor says.

With eradication of PCV2 not possible, more research is needed to define the role of viremia and reduce the incidence of circovirus infections in herds where PRRS, SIV and mycoplasma co-infections exist, he concludes.