It appears to be a new disease. And it already has a very descriptive name, which just about sums up current knowledge on it: Postweaning Multi-Systemic Wasting Syndrome or PMWS.
PMWS appears to be caused by porcine circovirus. But wait a minute. Didn't researchers talk about porcine circovirus a few years ago, and never found it much of a threat?
New Circovirus? Yes, that's true. Scientists say, however, this porcine circovirus is a different strain. And very possibly a big part of the difference is its link with porcine reproductive and respiratory syndrome (PRRS), which has been found in a majority of the PMWS cases in the U.S.
"We don't really know enough about the prevalence and the incidence to say how much of a problem porcine circovirus is," says Paul Sundberg, DVM, director of Veterinary Issues, National Pork Producers Council (NPPC).
To find out just how prevalent the virus is, NPPC is using production checkoff funding to move fast to get ahead of the curve, he stresses. We really need to find out what the disease is, how the virus is related to the syndrome, and how to control it before we can say how much of a threat it is to the health of herds, Sundberg stresses.
NPPC convened a summit on circovirus where they put out the call to industry to conduct basic research. NPPC has allotted about $95,000 for circovirus research. Proposals were due Aug. 7 with the research to be funded this year.
"The problem with this circovirus syndrome is that when you get weight loss in postweaning pigs, the list of possibilities can be very long and include infectious and non-infectious causes," explains Sundberg.
A lab diagnostician in Canada has reproduced the disease and the circovirus has been recovered after being given to germ-free pigs. John Lewis, DVM, University of Saskatchewan, says PMWS caused some of the lesions seen with the disease, but not all of them.
Tough Disease Back in the U.S., NPPC's Sundberg says he has heard from diagnostic labs that have been asked to look for the virus in Iowa, Indiana (Purdue), Minnesota and Nebraska. "But all of those labs also said they are not getting overwhelmed with cases," he notes.
Still, the few cases being reported concerns NPPC. In those cases, it's common to see 8- to -10-week-old postweaning pigs that are unthrifty, listless, develop rough hair, and have difficulty breathing.
Steve Sorden, DVM, at Iowa State University's (ISU) diagnostic lab, says there is no effective treatment for the syndrome. All antibiotics have been tried to no avail. "Producers have been seeing 10% death loss in their nurseries and they are trying to live with it," Sorden says.
His advice: If you see unthrifty pigs develop after weaning, don't wait for any further signs. Isolate those pigs immediately. Follow good management practices by paying attention to feed and water availability, housing conditions and good husbandry. Consider having a veterinarian submit a tissue sample to a lab.
Sorden adds he has just started to isolate this new circovirus from lungs and lymph nodes. These days his workload appears to be on the rise. There was one case reported to the diagnostic lab in the fall of 1996. After that, a case would pop up now and again. But this year, the lab has seen 65 cases. The lab now averages about two cases a week.
Perry Harms, DVM, who is at ISU pursuing a graduate degree studying porcine circovirus, says in herds with PMWS, 5-15% of a group of pigs are usually affected. He says at least half of the cases studied have also had PRRS. Pneumonia and salmonella have also been identified as secondary problems.
A bigger question to Sorden is how many pigs get infected but never show any clinical signs. "We say that 10% got sick. Are the other 90% not infected, or did they get infected and recover and we never saw it?" he questions. And why is it that when affected pigs are separated, some continue to waste away, while others recover, asks Sorden.
Source Of Infection In Iowa, most problems have occurred in farms that purchased imported feeder pigs, and sometimes early weaned pigs, according to Sorden.
In his view of these cases, not enough is known about PMWS to determine if porcine circovirus or PRRS is the primary disease agent. "We just know that they are together and we can identify that in the diagnostic lab," Sorden says.
At South Dakota State University's diagnostic lab, Kurt Rossow, DVM, says he has only seen six cases of this new porcine circovirus - and all six have had a dual infection with PRRS. He's seen Streptoccous suis, Pasteurella multocida and Haemophilus parasuis as secondary bacterial infections.
Other Countries "They've known about a porcine circovirus for about 20 years in Germany," Sorden says. "And basically it had not been associated with any disease. They did some studies where they looked at blood samples from slaughter pigs and found most pigs had antibodies to this virus, but they weren't able to associate any disease with it except there was some evidence that it might be involved with Shaker Pig Syndrome."
PMWS has also been detected in hog herds in France, Spain and Ireland.
Since 1995-96, it has been reported in western Canada. Some cases have been severe, affecting half the herd. Problems have been the least in the best-managed herds. Management practices like all-in, all-out have helped to reduce its impact.