Scientists warn: Rapidly-spreading swine disease has unknown source

MANHATTAN, Kan. – A new disease has taken swine producers, veterinarians and scientists across the country by surprise and left them searching for solutions. Formerly known as Post-weaning Multisystemic Wasting Syndrome (PMWS), Porcine Circovirus Associated Diseases (PCVAD) was discovered in the early 1990s by two Canadian veterinarians, John Harding and Ted Clark, said Lisa Tokach, an Abilene, Kan. veterinarian.
Harding and Clark associated the disease with an increased mortality rate in weaning pigs.
Contagious. “The first PCVAD case in Kansas was discovered in November 2005 and now we’re seeing new cases almost every week,” Tokach said.
“It is highly contagious and is spreading fast.”
She gave a presentation on PCVAD at Kansas State University’s annual Swine Industry Day in November. The PCVAD name was suggested by the American Association of Swine Veterinarians after the discovery of Porcine Circovirus type 2 (PCV2).
PCVAD can be used to describe all of the diseases attributed to porcine circovirus, including PMWS. The PCV2 disease was discovered when swine practitioners began reporting an increased number of PMWS cases in finisher pigs.
Through research trials and field cases, scientists discovered that the PCV2 disease was contributing to the increased presentation of PMWS in these swine herds.
Species specific. Unlike diseases such as West Nile Virus, PCVAD is species specific, meaning it doesn’t spread to other species, but other types of circoviruses have been found in birds, Tokach said.
It’s predicted that every swine herd in the United States is “infected” with PCVAD, however, not all herds are “affected,” she said.
“Infected” means that porcine circovirus type 2 is present in the herd, but clinical signs may not be present, whereas, “affected” means that the herd is displaying symptoms associated with the virus.
Environmental conditions and the presence of other pathogens or diseases may be contributing factors explaining the difference between “infected” herds and “affected” herds.
However, it is not yet clear what drives the disease. PCVAD depletes the lymph node system, leaving the pig with no defense against other pathogens.
When the pig becomes infected with another pathogen or disease, its body can’t defend itself, so most PCVAD-affected pigs die, Tokach said.
“We’re still learning a lot about PCVAD, but we do know that it is a viral condition in swine caused by PCV2 and it seems to have a wide variety of symptoms,” she said.
Solutions. She has been working closely with swine producers and a team of scientists who are studying PCVAD and other infectious diseases that affect it, to find possible solutions.
Scientists are conducting field studies and laboratory diagnostics, developing a disease model, and working with swine producers to test PCV2 vaccines, said Bob Rowland, virologist for Kansas State’s College of Veterinary Medicine.
“This is definitely a new approach to infectious disease research, in which we’re working closely with vets and producers,” Rowland said.
Scientists expect to have the vaccination study finished in about a month, but they are not sure when a vaccine will be available in sufficient amounts for producers to purchase.
“From a practitioner point-of-view, I’m seeing farmers lose up to 20 percent of their finisher pigs,” Tokach said. “This disease is not only economically devastating, but it’s emotionally devastating, too. That’s why we’re working so hard to find a cure or vaccine.”
There is currently one commercial vaccine available, but in limited amounts, she said. Some producers using the vaccine have been working with Tokach and the Kansas State scientists, giving them the opportunity to study the vaccine’s effectiveness in the field.
It’s too early to tell how effective this vaccine will be, but the preliminary trials look good, Tokach said. Scientists are also working to find a point of origin, such as a particular farm or possibly maybe a boar stud, but have had little success so far.
The disease seems to be spreading rapidly and randomly, making it difficult to predict where it may turn up next.
Symptoms. Some symptoms of PCVAD include: anorexia, rapid weight loss, generally unhealthy pigs, skin discoloration or lesions, respiratory problems and diarrhea, according to a brochure from the National Pork Board and the American Association of Swine Veterinarians.
The brochure recommends some management practices producers can follow to reduce the risk of a PCVAD outbreak and is available at www.aasp.org/aasv/documents/PCVADBrochure.pdf.
If producers suspect that their herds may be affected, Tokach recommends that they work with their veterinarian to collect tissue and blood samples to be tested.