Just as progress is being made on PRRS, another “mystery” disease surfaces.
The newest “mystery disease” is PMWS, or postweaning multi-systemic wasting syndrome. It shares many features with porcine reproductive and respiratory syndrome (PRRS):
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Both started out as mysteries to scientists and veterinarians;
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Both seemed to begin in Europe and slowly spread to North America;
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Both are very economically devastating in the most severe form;
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Both seemingly have a porcine-specific virus as their root cause;
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Both have distinct strains that dictate the severity of the disease; and
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Both have had scientists scratching their heads and arguing in the early stages of the syndrome.
The other similarity is the variation in clinical signs and severity between farms. Nearly every farm and population of pigs has evidence of circovirus — with some farms seriously impacted, and others showing little or no clinical signs. In some cases, there may be one finishing barn out of four with severe signs, while the pigs in the other three barns remain clinically normal.
Disease Symptoms
Up to half the pigs in a group can be affected in severe cases, but generally 10-20% are affected; nearly every pig that shows clinical signs of PMWS eventually dies. The clinical signs are pretty well described by the syndrome's name: postweaning multi-systemic wasting syndrome.
Most recently reported cases occur not only postweaning, but also post-nursery in the early stages of grow-finish production.
Many infected grower pigs carry a respiratory component of the disease in addition to the wasting syndrome.
Clinical signs, other than simply falling back, can be very subtle: increased respiratory rate, pale in color, rougher coat and slightly dehydrated. Often, the caretakers report: “The pigs just ain't doin' right.”
A small number of pigs in the group may have skin lesions or dermatitis, also often associated with kidney problems. This condition is referred to as PDNS, or porcine dermatitis and nephropathy syndrome.
Diagnosis
A definitive diagnosis of PMWS requires the veterinarian to observe clinical signs, perform a necropsy on a typical pig and submit tissues to a diagnostic lab for confirmation.
Control of PMWS
While there are no vaccines or treatments commercially available in the United States for PMWS, a number of management practices seem to help control this syndrome.
First, the producer must attempt to eliminate or minimize the effects of other pathogens commonly impacting pig populations, including PRRS virus, swine influenza virus, parvovirus and Mycoplasmal pneumonia.
Next, control the secondary bacterial pathogens such as Pasteurella multocida and salmonella with properly timed treatments.
Finally, reassess all management practices that have been helpful for other disease outbreaks:
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Adhere strictly to all-in, all-out pig flows;
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Decrease stocking density and utilize hospital pens or barns in order to promptly remove affected pigs;
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Minimize mixing and moving of unaffected pigs;
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If possible, stick to a single source of pigs from suppliers with no history of PMWS. It may also be crucial to switch genetic lines.
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Concentrate on all biosecurity protocols, and follow disinfectant measures to minimize the spread of viral pathogens.
Case Study
The manager of a 10,000-head finishing site called to report that “quite a few” pigs were falling back and beginning to appear unthrifty. This group of pigs had been placed about eight weeks earlier, and had been performing well to that point. It was late summer, and since the new corn crop had yet to reach the mill, the manager was concerned about feed quality and the affect it could be having on the pigs.
Upon examination, I found that 5% of the pigs marked as “fall behinds” were obviously distressed and had a slightly increased respiratory rate. One pig had PDNS lesions.
At necropsy, I found that the affected pigs had rather mild lung lesions and marked edema of the spiral colon, along with a slight jaundice. Blood and tissues were collected and immediately submitted to the diagnostic laboratory.
The manager immediately removed the affected pigs to hospital pens and treated them individually with a broad-spectrum, long-acting injectable antimicrobial to address the respiratory component of the symptoms.
Attention was given to ventilation, temperature, stocking density and feed quality to assure optimal pig comfort.
While the laboratory confirmed moderate lesions indicative of PMWS and the presence of porcine circovirus Type 2, the early intervention in this case appeared to forestall severe losses.
