Producers and veterinarians alike are struggling to find ways to manage a tiny, common swine virus, and understand why it is suddenly creating havoc in a growing number of U.S. finishing barns.
Porcine circovirus is no stranger to the pig world. It's been regularly diagnosed in U.S. herds for years. In fact, there are only five or six herds known worldwide that have actually tested negative for the virus.
Iowa State University (ISU) has documented several hundred cases of the virus dating back to the late '90s. But its true impact on production has been questioned in a number of veterinary circles in recent years.
That's certainly no longer the case. Last fall, porcine circovirus-associated disease or PCVAD (formerly known as postweaning multi-systemic wasting syndrome or PMWS), began to inflict heavy losses across the hog belt.
“What catches our attention is we are putting interventions in and we are continuing to lose pigs,” says Joe Connor, DVM, Carthage Veterinary Service, Ltd., Carthage, IL, in a talk at World Pork Expo. Producers are going full throttle on management and adding high levels of antibiotics to finisher rations — and still not achieving satisfactory results.
Connor says clients are reporting mortality rates above 35% and morbidity rates greater than 50% in some barns and in repeated groups in a system.
Pigs are most commonly affected at about 4-5 weeks after placement in a finisher, with the biggest impact over a 2- to 4-week period.
“All of a sudden those pigs develop a history of wasting, when they will lose almost half of their body weight,” notes Connor. They also frequently have co-infections, including porcine reproductive and respiratory syndrome (PRRS), swine influenza virus (SIV) and Mycoplasmal pneumonia. Enteric infections and diarrhea in the suckling pig have also been seen, and some growing pigs have ileitis-like diarrhea.
The role of PCVAD in reproductive disorders needs further investigation, he says.
The Illinois swine veterinarian also reports occasional problems in herds without co-infections. One producer's 1,200-sow, farrow-to-finish herd is PRRS-negative, SIV-negative and mycoplasma-negative. Due solely to PCVAD, he saw a sudden increase in mortality in which he lost about 20% of pigs the first four weeks after moving them into the finisher. Nursery mortality remains normal at 1.4% on an eight-week schedule.
When pigs infected with PCVAD are necropsied, the lungs look like a very typical PRRS infection: heavy, wet, dense and rubbery. Severely affected pigs have “tremendously enlarged lymph nodes,” he says. Hearts often appear enlarged. There can also be liver and or kidney failure.
A small percentage of pigs will appear yellow or jaundiced with severe anemia.
Another clinical sign diagnosed in 1-10% of PCVAD cases is porcine dermatitis and nephropathy syndrome (PDNS), typified by hemorrhages and discoloration to various parts of the body.
“The interesting thing with PDNS is 80% or more of those pigs end up dying,” remarks Connor. “There is a very, very low recovery rate, but a lot more work needs to be done to determine if PDNS is really part of this syndrome.”
In Europe, best management practices have really been reemphasized to reduce the impact of this syndrome, he says. Focus has been on all-in, all-out pig flow, batch farrowing and intensive cleaning and disinfecting premises. These approaches have taken a tremendous amount of work and discipline.
Still, the results have only been partly successful. Herds that were typically averaging 3% mortality during wean-to-finish production shot up to 12-15% with PCVAD. After intensive management, mortality has settled back down to about 8%.
Connor says Europe has had some success with reducing pen size, whereas, in the United States producers have moved to large pen populations, which may in fact aggravate this syndrome.
The other challenge is ensuring that barns that are pushed to maintain pig flow are properly dried after cleaning and disinfecting, he comments.
Clearly, one of the keys to control of PCVAD will be introduction of vaccine, says Connor.
Fort Dodge Animal Health (FDAH) has received full licensure from the U.S. Department of Agriculture for the first vaccine for PCVAD. Suvaxyn PCV2 One Dose is labeled as an inactivated, one-dose vaccine for piglets 4 weeks of age and older to aid in the prevention of Porcine Circovirus Type 2 viremia (the presence of virus in the blood) and control of lymphoid depletion (infection of the lymph nodes) caused by PCV2.
“As an inactivated vaccine, there is no danger of reversion to virulence or potential for it to combine with field strains,” reports Darrell Neuberger, DVM, swine technical manager for FDAH. One dose provides convenience and labor savings, he says. Field trials of more than 1,000 pigs showed no adverse events associated with vaccination.
Work on the vaccine started more than six years ago and was a collaborative effort between Virginia Tech, Iowa State University and FDAH. Studies show the vaccine virus induces protective immunity against Type 2 porcine circovirus, while retaining the non-pathogenic nature of Type 1 porcine circovirus.
Duration of immunity is four months to provide long-term protection through finishing, says Neuberger.
Although the product has not yet been licensed in Canada, swine veterinarians there have petitioned Agriculture Canada for an emergency license of the FDAH vaccine for PCV2.
Fort Dodge Animal Health is gearing up vaccine production to meet the needs for Suvaxyn PCV2 One Dose for both the United States and Canada.
“Certainly it is not a vaccine that is going to be used as a blanket across every pig herd in the United States. But in these herds that are experiencing PCV2 problems, it certainly will be used. We have had tremendous demand for this product,” he says.
Neuberger says FDAH is also working on a combination vaccine that would address problems with porcine circovirus and co-factors.
For more information on FDAH's circovirus vaccine, contact Joe Barban, swine business manager for FDAH, at (800) 477-1365, or log onto www.stopcircovirus.com to learn more about PCVAD. The site is linked to ISU's veterinary diagnostic laboratory Web site so swine practitioners can access information they need relative to submission of samples to ISU, says Barban.
Iowa State University's Pat Halbur, DVM, reports that out of about 480 cases of porcine circovirus-associated disease (PCVAD), only nine submissions to the veterinary diagnostic laboratory featured circovirus infection alone.
Secondary factors or co-factors commonly add to the severity of circovirus syndrome. Porcine reproductive and respiratory syndrome (PRRS), Mycoplasmal pneumonia and salmonella create the biggest headaches, says John Kolb, DVM, Boehringer Ingelheim Vetmedica, Inc. (BIVI).
Less often you will find swine influenza virus, Haemophilus parasuis and Streptococcus suis.
What these co-factors do is add to the levels of porcine circovirus in serum and tissues, he says.
In 70-80% of cases, the pig's immune system seems to be able to deal with the circovirus, states Kolb. But in 10-20% of cases, something triggers continued growth of the virus that destroys the immune system, pigs respond poorly to treatment and often die.
Figure 1 depicts self-reported cases of PCVAD in the United States.
Kolb says BIVI is about halfway through a research project to determine common co-factors. So far PRRS seems to be at the top of the list. He says PRRS virus is probably present in about 90% of cases of circovirus.
For PRRS, the best option is to depopulate the nursery. If that's not possible, he recommends using vaccination to control PRRS and other co-factors. To get out in front of this virus, move vaccination ahead of exposure (early finisher) and vaccinate during the early nursery phase of production at the latest.
In research at Iowa State University, pigs vaccinated against PRRS with BIVI's Ingelvac PRRS ATP, and then experimentally challenged with circovirus five weeks later, were protected against PRRS virus challenge. Even when PRRS vaccine was given at almost the same time as circovirus infection occurred, the PRRS vaccine still afforded some protection and improved gain, says Kolb. Field trials have shown similar results with early vaccination.
To learn more about PCVAD, a research project is being launched by BIVI, modeled after the company's PRRS research awards. BIVI is committing $75,000 annually to fund three selected research programs. The program is open to all swine researchers, veterinarians, academia and others within North America.
“The goal of the PCVAD Research Award Program is to fund collaborative research efforts that we hope will bring the entire industry together and lead to practical, clinically relevant solutions that veterinarians and producers can use to prevent or manage the disease and conditions associated with them,” says Klaas Okkinga, product marketing manager with BIVI.
Research proposals are being accepted until Aug. 15. The first three grants will be awarded at the Leman Swine Conference, Sept. 23-26 in St. Paul, MN.
— Joe Vansickle
Recent research from Iowa State University (ISU) shows that vaccinating for Mycoplasmal pneumonia reduces the severity of porcine circovirus-associated disease (PCVAD) in circovirus and mycoplasma-infected herds.
Vaccinating for mycoplasma has also been shown to be effective in the face of porcine reproductive and respiratory syndrome (PRRS).
Co-infections of porcine circovirus type 2 and mycoplasma add to the severity of PCVAD. New research shows that with appropriate use and timing of mycoplasma vaccination with RespiSure (Pfizer Animal Health; www.pfizerah.com), production losses from the two diseases are minimized.
In the study, 296 early-weaned barrows recorded higher body weights and average daily gains, lower lung scores and, in general, had fewer clinical signs of disease than control pigs. The research also signaled that mycoplasma vaccines did not increase levels of circovirus in pigs.
Patrick Halbur, DVM, Tanya Oppriessnig and Eileen Thacker, DVM, all of Iowa State University, performed the protocol development and analysis. Veterinary Resources, Inc., Ames, IA, implemented the study and generated the data. Results were presented at the American Association of Swine Veterinarians annual meeting this year in March in Kansas City, MO.
“Our research showed that vaccinating for mycoplasma reduces the severity of PCVAD in porcine circovirus type 2 and mycoplasma-infected herds,” says Halbur. “We also found that vaccines with either oil- or aqueous-based adjuvants have been shown to improve the clinical picture and performance in co-infected herds. Vaccination against mycoplasma is imperative.”