Opportunities for nickels and dimes have greater impact when profit margins are tight. For example, occasional lameness in finishing pigs and discounts at slaughter are common realities that sometimes seem beyond our control. However, recent research suggests that we could still improve diagnosis and control of an “old disease” – erysipelas.
Erysipelas continues to affect pigs worldwide, with economic losses stemming from disease outbreaks or animals being condemned at slaughter. It is estimated that 30-50% of swine harbor Erysipelothrix rhusiopathiae, the causative agent of swine erysipelas. Pigs carrying E. rhusiopathiae, shed the organism and are thought to be the source of infection for acute outbreaks of erysipelas, which often follow a stress-inducing event.
Pigs can be infected with erysipelas without signs, or can suffer clinical disease ranging from lameness, septicemia, skin lesions, or they can suddenly die without signs of disease. Herd or barn outbreaks of erysipelas are typically due to acute bacterial septicemia, which may include fever, decreased feed intake, depression, reluctance to move and often the classic rhomboid skin lesions (diamond skin disease). Lameness (arthritis) and inflammation of the heart valves (endocarditis) are more chronic forms of the disease.
Economic losses occur from increased numbers of acute deaths, treatment costs, vaccination costs and slow growth of diseased pigs. In addition, there is economic loss from slaughter condemnations or trimming that is often unexpected, yet economically significant. It is frustrating for both producers and veterinarians when disease or slaughter condemnations occur despite implementation of vaccination and control strategies.
Carcass Condemnations
Data collected from the United States Department of Agriculture (USDA) and USDA’s Food Safety Inspection Service (FSIS) is summarized in Figure 1. Swine erysipelas continues to be associated with condemned swine carcasses, and ranks in the top 10 causes for swine condemnations from 2003-2008, continuing previous trends. Furthermore, it is unknown how many of the slaughter condemnations classified as septicemia or arthritis are actually due to swine erysipelas.
A visual diagnosis of swine erysipelas can be challenging for inspectors at slaughter plants as several diseases can manifest with similar signs. Interestingly, over the past 10 years, trends show that when erysipelas condemnations increase, condemnations due to septicemia and arthritis increase as well (Figure 2). This suggests the full economic impact of erysipelas to the swine industry perhaps is underestimated.
Causes
There are many potential causes for septicemia, arthritis or skin lesions. Some of the differentials for clinical signs of erysipelas may include: Actinobacillus suis, Haemophilus parasuis, Staphylococcus hyicus, Streptococcus suis, Mycoplasma hyosynoviae, osteochondrosis, fungal agents, porcine dermatitis and nephropathy syndrome, rickets, and a host of others.
Recent work at the Iowa State University Veterinary Diagnostic Laboratory (ISU-VDL) has expanded the diagnostic capabilities available to veterinarians and producers. By revisiting and modifying some previously described methods, the ISU-VDL has increased the ability to detect, isolate and identify cases of swine erysipelas, either from field cases or from specimens from slaughter facilities.
Improved Diagnostics
The ISU-VDL has recently improved diagnostic methods for isolating the organism from affected organs (spleen, liver, kidney, lung, heart, skin, lymph nodes, joint fluid) by using a modified enrichment process. Immunohistochemistry can identify the organism in formalin-fixed tissues (skin, synovium, kidney, spleen, liver, heart, lungs). Serotyping and polymerase chain reaction (PCR) can also be used to determine the specific characteristics of an Erysipelothrix isolate. Some isolates and types are known to be more pathogenic than others.
Diagnostic data from the ISU-VDL data warehouse indicates the incidence of swine erysipelas to be relatively constant throughout all seasons with no clear seasonal effect. Erysipelas is not just a late spring/early summer disease, but is detected year-round. (Figure 3).
Submitting Samples
When clinical signs are suggestive of swine erysipelas, samples can be submitted to a veterinary diagnostic laboratory for confirmation. Tissue submissions from suspected acute outbreaks of erysipelas should be from non-medicated pigs and include: lung, liver, heart, spleen, kidney, skin lesions, tonsil and joint fluid. Multiple tissues should be submitted because E. rhusiopathiae is not always present in all organs and other types of insults need to be ruled out.
In the more chronic cases of swine erysipelas, lameness may be more prevalent and the entire affected joint along with the other tissues mentioned for acute disease are recommended for submission to a laboratory. In either case, both chilled (not frozen) fresh, as well as formalin-fixed tissue samples, should be included from non-treated animals. If tonsil is included, it should be placed in a separate specimen bag. E. rhusiopathiae can be present on the tonsil of normal swine and isolation of E. rhusiopathiae from tonsil will confirm infection, but does not confirm disease (erysipelas).
Control is Key
Despite being one of the oldest and most recognized diseases in the swine industry, erysipelas continues to be a challenge to control, in part because E. rhusiopathiae is ubiquitous in the environment and is carried by several different animal species (birds, fish, rodents). These features of the bacteria complicate prevention and make eradication nearly impossible. Herd losses can be quantified based on cost of prevention, treatment, and death loss, but it is difficult to quantify losses associated with full or partial slaughter condemnation. Prevention is best achieved through implementing reliable management practices and through use of commercially available vaccines.
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Joe Bender and Darin Madson, DVM
Iowa State University Veterinary Diagnostic Laboratory
madson@iastate.edu