Circovirus Poll

Sep 15, 2007 12:00 PM, By Joe Vansickle Senior Editor

University of Minnesota survey offers insight into disease symptoms and veterinary experiences.

In 2006, porcine circovirus-associated disease (PCVAD) struck half of the finishing sites attended by U.S. swine veterinarians who relied on laboratory confirmation of the disease, according to a University of Minnesota survey of members of the American Association of Swine Veterinarians.

Peter Davies, DVM, Leman Chair in Swine Health and Productivity at the university, sent out questionnaires asking for observations on approaches to diagnosis of PCVAD. About 90% of veterinarians typically rely on diagnostic laboratory support when diagnosing PCVAD. The National Pork Board funded the project.

Of the 214 veterinarians who responded (44%), 172 were actively involved in swine medicine, 61% in private practice. Another 26% worked in corporate production systems and 18% as swine consultants (the total exceeds 100%, as a veterinarian could select multiple choices).

Of these respondents, 146 (85%) based in 17 states had diagnosed porcine circovirus type 2 (PCV2) last year, “indicating the widespread nature of the disease,” says Davies. The total of estimated sites affected with PCVAD was more than 3,700, although some sites could have been counted twice.

Furthermore, among the PCVAD-affected sites, about 70% were reported to have experienced a threefold increase in mortality associated with PCVAD outbreaks, and about 46% were estimated to have experienced finishing mortality of 15% or greater in at least one group at a site, he says.

In four of the five states where respondents had not reported PCVAD, (Georgia, Idaho, Michigan and North Dakota), only one veterinarian per state responded to the survey. And in the fifth state (Oklahoma), none of the four veterinarians surveyed had diagnosed PCVAD in finishing pigs in 2006, Davies observes.

Disease Symptoms

Veterinarians were asked how often they observed different clinical signs of PCVAD. Four main symptoms are ranked in Figure 1: wasting syndrome, porcine dermatology and nephritis syndrome (PDNS), respiratory signs and diarrhea. The proportions of these symptoms ranged from 0% to 100%.

However, for both wasting (33% of veterinarians) and respiratory signs (20% of veterinarians), the most common response was that these symptoms occurred in all outbreaks they had diagnosed.

In contrast, 34% of veterinarians estimated PDNS occurred in 10% of PCVAD cases, and another 18% of veterinarians indicated PDNS was observed in 20% of the cases.

Diarrhea was estimated to have occurred in 50% of cases by 19% of veterinarians surveyed.

Swine veterinarians provided interesting comments about their experiences in dealing with PCVAD:

“My personal opinion on PCVAD is that the presence of clinical signs is still following an initiating event. As veterinarians, we believe that this event would need to be some disease organism. But if the event needs only to stimulate the immune system, it could be several different stimulae, including airborne dust, pit gases or mycotoxins.”
“What a unique disease…all we would see is that within 12-24 hours, pigs would just lose their color, but otherwise look normal. We would know that those pigs were ‘goners.’”
“No disease has been so terrible on both the dollars and the crew taking care of affected pigs.”
“PRRS has been a big factor in many of our cases, and it has been critical to get PRRS under some control (reduced level of infection at weaning) in order to allow PCV2 vaccines to work. I have not seen this many herds affected with this kind of mortality in any period of my 30 years in practice.”
“We are rapidly resolving all cases that have been vaccinated, and that percentage is increasing. We have almost no farms on which a confirmed laboratory diagnosis has not been accomplished. Incidence of slow-growing and ill-thrift pigs has increased as mortality has stabilized or decreased.”

Davies comments that early reports suggest vaccination efforts for preventing PCVAD in the United States “have been extraordinarily positive.” And now most veterinarians he has spoken to lately indicate there is adequate availability of vaccine for PCVAD.

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