The diversity in clinical signs of porcine circovirus-associated disease (PCVAD) has swine veterinarians perplexed in finding common themes and treatment regimens to make a dent in this disease complex.
Six months ago, swine veterinarian Keith Erlandson and his colleagues at Carthage (IL) Veterinary Service weren't too worried about PCVAD. Occasionally, an individual pig would get sick and they'd try to treat it.
However, reports of some serious problems in Canada soon heightened concerns, followed by a few isolated cases of high mortality in finishing pigs about four months ago.
“Then about two months ago, all heck broke lose,” Erlandson says. “Producers were calling to report fall-off pigs all over the barn. They would swear they weren't there yesterday.”
Another common observation producers are making is more graphic: “Producers will call and say, ‘We've got pigs with purple ears and purple butts; it kinda looks like salmonella, but kinda not. We've shot the heck out of these rainbow pigs (referring to the multitude of treatment marks on the pigs), but they just never respond,”’ he adds.
Erlandson shares producers' frustrations in trying to find anything that works against PCVAD. “It is very disheartening to me to go out and look at rainbow pigs and try to think of some therapeutic in my arsenal I can tell this producer to use that is going to help his pigs. We've tried several therapeutic strategies, and many times none of them have seemed to work.”
The Illinois swine veterinarian says the most common co-infections implicated with PCVAD in his practice include porcine reproductive and respiratory syndrome (PRRS), Mycoplasmal pneumonia, salmonella, swine influenza virus and E. coli.
Even PRRS serum inoculation has been blamed for igniting PCVAD problems. “Some of the veterinarians in our clinic say they have really seen an increase in circovirus in herds that have undergone serum therapy,” he says.
Erlandson says equally frustrating is the inability to find a pattern or common denominators in herds that get infected with PCVAD.
“I've got well-managed, PRRS-negative, mycoplasma-negative herds and there is nothing they can do to save the pigs. I've seen herds that are PRRS-positive and mycoplasma-positive that get PCVAD, but other PRRS-positive and mycoplasma-positive herds that never seem to get any circovirus-associated disease,” he explains.
Vaccination for PCVAD has been implemented in a number of production units experiencing problems, he says. But product has been in short supply in the face of heightened demand. Fort Dodge Animal Health's Suvaxyn PCV2 One Dose is currently the only fully licensed vaccine for PCVAD. Several other companies are reported to have vaccines waiting in the wings.
Erlandson recently spoke at a PCVAD Strategic Planning Workshop in South Sioux City, NE, sponsored by the National Pork Board, to develop research priorities.
In a talk at the George Young Swine Conference just preceding the Pork Board workshop, Nebraska swine veterinarian Keith Schumacher of Howells, NE, says he has heard comments about moving to small finishing pens to combat the effects of PCVAD. However, his clients with large-pen finishing rooms (250-500 head) have had fewer problems in general than other producers with small, 30-head finishing pens.
Typically, operations will go through “3-4 weeks of just like a nightmare to get through circovirus,” he explains. In his practice, Salmonella cholerasuis is a common co-infection. In the past, salmonella breaks lasted 7-10 days. With PCVAD, salmonella problems can last three weeks, he adds.
Recent outbreaks include a trio of players: circovirus coupled with salmonella and PRRS virus. To a lesser extent, circovirus co-infections consist of Streptococcus suis, Pasteurella multocida, mycoplasma, ileitis and a little bit of swine influenza.
Many pigs with PCVAD will look like a greasy pig, but often perform similar to normal-appearing penmates, he says.
Schumacher has not had much success using antibiotics to control disease factors associated with PCVAD. “But anti-inflammatory drugs (aspirin) have proven helpful in reducing viremia (the presence of virus in the blood) and fever, stimulating appetite and just making the pigs feel better.
“Inferon alpha pulsed in the water once a day for 20 days has been implemented to try and help reduce viremia,” he says.
While it has been difficult to identify proper control measures for PCVAD, Schumacher believes it is important to focus on environment and pig comfort. “If you have really healthy pigs, you can get away with being lax on a lot of that stuff. But if you have a lot of bugs in there, those things can really come back and bite you,” he stresses.
The bulk of PCVAD cases that Pipestone (MN) Veterinary Clinic swine veterinarian Cameron Schmitt sees are in the pigs ranging from 90-130 lb., commonly observed as wasting, mild diarrhea and pale pigs that get stomach ulcers.
What's striking to Schmitt is that when he submits samples to the diagnostic lab, circovirus is invariably present in low levels in lymphoid tissues in pigs of all ages, from birth to market. He says surveys of slaughter hogs have shown a high prevalence of circovirus.
He suggests the disease is also sex-linked. “We lose 2-3 times as many barrows to this disease as we do gilts,” he relates.
Circovirus-salmonella co-infections are controlled through vaccinating for salmonella. Circovirus-ileitis co-infections are more common; vaccine has worked fairly well to control ileitis.
Pneumonia problems linked to PCVAD can be severe, and he has yet to find an antibiotic that works consistently to treat it.
Economic Case Study
Tom Gillespie, DVM, Rensselaer, IN, provided a glimpse at what PCVAD can cost an operation. A 1,200-sow, two-site production unit in Indiana was producing 26-27 pigs weaned/mated female/year during 2002-2004. PRRS-naïve weaned pigs were overstocked into conventional nursery and finishing barns.
In late 2004, the system was diagnosed with pneumonia, a variant form of H3N2 swine flu, but no PRRS virus. Lymphoid depletion with porcine circovirus Type 2 (PCV2) was present, and a histological (tissue) diagnosis of inflammation by the pathologist supported the clinical disease expression. The herd was experiencing PCVAD, he says.
The disease challenges produced the following changes in production:
A 3.24% increase in finishing mortality, producing an increase in costs of $2.78/pig;
A loss of 22.7% in average daily gain, valued at $2.09/pig; and
A loss in feed efficiency of 0.23 g./pig, worth $1.73/pig.
In all, the direct loss from the disease insult came to $6.60/pig. Based on 13,300 pigs placed during the six-month period of PCVAD losses, there was a lost opportunity of $87,780.
Gillespie says those losses due to PCVAD during 2004-2005 actually constituted a $100,000 difference in returns, because the feed the dead pigs consumed, which was not counted as a loss in the above numbers, was instead included with the feed consumed by the live pigs.
But that still doesn't tell the whole story of the impact of PCVAD and related diseases, he says. Before the disease bout, 90% of all weaned pigs went to market.
In contrast, based on the last set of 1,073 pigs placed in the finisher, 635 were marketed, 255 were lights, 110 were “off pigs” that the producer didn't receive value for, and 73 died.
“Suddenly we were dealing with 7% mortality and almost 24% lights and culls. We ended up marketing just 59% of the pigs that were placed in a typical 1,000-head finisher room. That's the true cost of this disease. It's the deads that get our attention. But what do we do with these lightweight pigs and under-market value pigs?” questions Gillespie.
He points out the costs of PCVAD are “very, very similar” to the cost of a PRRS break.
PCVAD Task Force
The American Association of Swine Veterinarians (AASV) has developed a PCVAD Task Force with members from the United States, Mexico and Canada, says task force chairman Gillespie. He spoke at a PCVAD conference sponsored by Boehringer Ingelheim Vetmedica, Inc., held at their Swine Health Management Center in Ames, IA.
The main thrust of the task force is to explore epidemiology — “where this disease is and where it is going,” explains Gillespie.
He says the key disease characteristics of PCVAD include a doubling of mortality and attrition — pigs that don't make market weight. PCVAD exists in many forms — reproductive, respiratory and enteric — well documented by European experience.
The University of Minnesota and Purdue University are coordinating an effort to track PCVAD cases worldwide.
The National Pork Board, using $300,000 in Pork Checkoff dollars and $200,000 in funding from the U.S. Department of Agriculture (USDA), has assigned 10 projects to researchers in the United States and Canada, according to Pam Zaabel, DVM, director of Swine Health Information and Research for the Pork Board.
“We asked the USDA to allocate funds for PCVAD because it is a high priority for the industry,” she explains.
The projects look at the unique causes of PCVAD, strain or type differences, immune responses, transmission, pathogenicity or how disease develops, the role of co-factors and biosecurity.
Zaabel's goal is to build a specific research initiative at the Pork Board to address PCVAD issues similar to the PRRS Initiative.
Circovirus Cases on the Upswing
Diagnosticians have been identifying porcine circovirus in pig tissues for quite a long time at the Iowa State University (ISU) Diagnostic Lab in Ames, according to Kent Schwartz, DVM.
Over time, the swine circoviruses have seemingly evolved and grown in virulence. It used to be that non-pathogenic Type 1 was most common. In recent years, pathogenic Type 2 has become more prevalent than Type 1.
As it has become more prevalent in the swine herd, porcine circovirus Type 2 (PCV2) has caused more damage as it teams up with a seemingly endless variety of co-infections, Schwartz reported during the George Young Swine Conference in South Sioux City, NE.
After somewhat of a dip in cases submitted to the ISU lab in the last few years, Schwartz has seen a resurgence in porcine circovirus-associated disease (PCVAD) positive samples submitted to the lab in the last 12 months.
“What has really struck me in the last couple of years is the amount of PCV2 associated with inflammation that we are seeing in multiple organ systems of the pig,” he says.
Schwartz postulates that inflammation and immune response associated with co-infections or co-factors can augment PCVAD severity. The virus seems to zero in on areas of inflammation to make conditions worse, he continues. The virus is transported in blood and likes to localize in lymph nodes and lymphoid tissues.
In some cases, gastric ulcers contribute substantially to high mortality, he comments. He reports of the 30% spike in finisher mortality in his own hog operation, 10% was traced to gastric ulcers and circovirus, with not much else detected at the time of death.
He reminds veterinarians and technicians not to forget to cut open the stomachs of submitted pigs to check for this ulceration.
While lungs are often damaged by PCVAD, increasingly, Schwartz finds cases where lungs are okay but the intestines, kidneys or other vital organs are severely affected.
The bottom line is that quite a few different tissues can be affected by circovirus, making diagnosis of PCVAD and host co-infections in each case a unique challenge, he points out.
Select three acutely affected pigs and a couple of chronically affected pigs and submit a complete set of tissues for laboratory work-up to identify agents associated with disease and mortality.
This information can be supplemented by a serological profile (for example, porcine reproductive and respiratory syndrome virus, swine influenza virus, Mycoplasmal pneumonia) of 5-10 pigs at several time points leading up to and following peak mortality.
“Often, peak mortality is a crescendo of the effects of infections occurring in previous weeks. Careful selection of pigs several weeks before peak mortality will likely reveal the agents that will be associated with peak mortality,” says Schwartz.
For producers/veterinarians working with Boehringer Ingelheim Vetmedica, Inc. (BIVI) on PCVAD, the company has developed MAGIC — Monitoring Assignment for Global Insight into Circovirus.
The goal of the program is to understand how the syndrome is linked to farm practices and how the disease impacts pig production, says BIVI's John Kolb, DVM.
The process starts with a serological screening of the breeding herd to establish a case diagnosis of PCVAD.
Then five pigs are selected for further diagnosis — four sick pigs and one healthy pig. Samples are collected at specific times during and before peak mortality to attempt to define all of the specific disease agents at work in the herd, says Kolb.
Kent Schwartz, DVM, Iowa State University (ISU) Diagnostic Lab, conducted a pig necropsy session during a recent swine conference on porcine circovirus-associated disease (PCVAD), hosted by Boehringer Ingelheim Vetmedica, Inc. Swollen mesenteric lymph nodes are a good sign that salmonella or porcine circovirus Type 2 (PCV2) may be present.
In the second panel, Schwartz dissects a lung with lesions of interstitial pneumonia; this is not specific for a particular disease agent, but is often associated with multiple agents and co-infections.
The yellowish abscess appears to be due to improper pig castration procedures, emphasizing that not all diseases or wasting conditions are infectious
In finishing up a necropsy, Schwartz stresses that it's vital to post several pigs to confirm a pattern of disease. Laboratory assistance is helpful to determine which agents are involved before making a disease diagnosis.