Erysipelas in pigs is an infectious disease caused by Erysipelothrix rhusiopathiae. It is one of the oldest recognized diseases that affect growing and adult swine.
Etiology and Pathogenesis of Swine Erysipelas
E rhusiopathiae commonly resides in the tonsillar tissue, and pigs often become healthy carriers. These typical healthy carriers can shed the organism in their feces or oronasal secretions and are an important source of infection for other pigs.
Infection is transmitted via ingestion of contaminated feed, water, or feces and through skin abrasions. When ingested, E rhusiopathiae can survive passage through the hostile environment of the stomach and intestines and can remain viable in feces for several months.
On farms where E rhusiopathiae is endemic, pigs are exposed naturally to the organism when they are young. Maternal-derived antibodies provide passive immunity and suppress disease. Older pigs tend to develop protective active immunity as a result of exposure to the organism, which does not necessarily lead to disease.
Recovered pigs and chronically infected pigs can become carriers of E rhusiopathiae. Healthy swine also can be subclinical carriers.
Clinical Findings of Swine Erysipelas
Outbreaks of swine erysipelas can be acute or chronic, and clinically inapparent infections also occur. Acute outbreaks are characterized by sudden and unexpected deaths, febrile episodes, decreased appetite, painful joints, and skin lesions that vary from generalized cyanosis to the often-described diamond skin (rhomboid urticaria) lesions.
Acute erysipelas outbreaks tend to be followed by chronic erysipelas, which is characterized by enlarged joints and lameness. A second form of chronic erysipelas is vegetative valvular endocarditis. Pigs with valvular lesions might exhibit few clinical signs. With physical exertion, however, they can show signs of respiratory distress, lethargy, and cyanosis, and possibly suddenly succumb to the infection.
The acute and chronic forms of swine erysipelas can occur in sequence or separately. Pigs that succumb to the acute septicemic form can die suddenly without previous clinical signs. This acute form of the disease occurs most frequently in growing and finishing pigs.
Outbreaks of swine erysipelas can be related to stressful conditions, such as extreme heat during transportation. Acutely infected pigs are depressed, febrile (40–42°C [104–108°F]), and reluctant to stand and move. Affected pigs squeal excessively when handled, require assistance to stand, and prefer to lie down soon after being forced to stand. They might also walk stiffly on their toes and shift weight from limb to limb when standing.
Anorexia and thirst are common signs of swine erysipelas, and febrile pigs often seek wet, cool areas to lie down. Skin discoloration can vary from widespread erythema and purplish discoloration of the ears, snout, and abdomen, to diamond-shaped skin lesions almost anywhere on the body, but particularly on the lateral and dorsal regions.
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Erysipelas lesions can occur as discrete, pink or purple areas of varying size that become raised and firm to the touch within 2–3 days after the onset of illness (see skin lesions image). These lesions might disappear over the course of a week or progress to a more chronic type of lesion, commonly referred to as diamond skin disease. If untreated, necrosis and separation of large areas of skin can occur, and the tips of the ears and tail can become necrotic and slough.
Courtesy of Dr. Ranald D. A. Cameron.
Clinical signs of swine erysipelas are usually sporadic and affect individuals or small groups; however, larger outbreaks sometimes occur. The mortality rate varies from 0% to 100%, and death can occur up to 6 days after the first signs of illness. Acutely affected pregnant sows might abort, probably as a result of fever, and lactating sows can show agalactia.
Untreated pigs can develop the chronic form of erysipelas, usually characterized by chronic arthritis, vegetative valvular endocarditis (see endocarditis image), or both. Such lesions can also occur in pigs with no previous signs of septicemia. Valvular endocarditis is most common in mature or young adult pigs and is frequently manifested by death, usually resulting from embolism or cardiac insufficiency.
Courtesy of Dr. John Prescott.
Chronic arthritis, the most common form of chronic erysipelas infection, produces mild to severe lameness in pigs. Affected joints can be difficult to detect initially; eventually, however, they become hot and painful to the touch and then visibly enlarged. Dark purple, necrotic skin lesions that commonly slough can occur. The mortality rate in chronic cases is low, but the pig's growth is slowed.
Lesions of Swine Erysipelas
At necropsy, pigs acutely infected with erysipelas can exhibit skin lesions, enlarged and congested lymph nodes, edematous and congested lungs, splenomegaly, and hepatomegaly. The kidneys and heart can show petechial hemorrhages.
In chronic erysipelas, valvular endocarditis is evident as proliferative, granular growths on the heart valves, and embolisms and infarctions can develop. Arthritis can involve joints of one or more legs, as well as intervertebral articulations.
Joints affected by chronic erysipelas can be enlarged, with proliferative, villous synovitis and increased viscosity of synovial fluid, inflammatory exudates, and thickening of the joint capsule. Proliferation and erosion of articular cartilage can result in fibrosis and ankylosis of the joint.
Diagnosis of Swine Erysipelas
Clinical signs and/or gross lesions
Response to antimicrobial treatment
Demonstration of the bacterium or DNA in tissues (bacterial culture and/or molecular tests)
Diagnosis of erysipelas is based on clinical signs, gross lesions, response to antimicrobial therapy, and demonstration of the bacterium or DNA in tissues from affected animals.
Acute erysipelas can be difficult to diagnose in individual pigs showing only fever, poor appetite, and listlessness. In outbreaks involving several animals, however, the presence of skin lesions and lameness is likely in at least some cases and would support the diagnosis.
Rhomboid urticaria or diamond skin lesions are almost diagnostic of erysipelas when present. However, similar lesions can occur with classical swine fever or African swine fever, Actinobacillus suis septicemia, and porcine dermatitis and nephropathy syndrome.
Isolation of E rhusiopathiae from blood of affected pigs, especially after enrichment, is possible in acute cases and helps establish a diagnosis. In addition, molecular methods capable of detecting E rhusiopathiae DNA in affected tissues or blood (ie, PCR assays) can be used.
Immunohistochemical methods to demonstrate the presence of E rhusiopathiae in formalin-fixed, paraffin-embedded tissues are available. These methods are useful when pigs have been treated with antimicrobials before sample submission.
Rapid, positive response to penicillin therapy in affected pigs supports a diagnosis of acute erysipelas because of the susceptibility of E rhusiopathiae to this antimicrobial.
Chronic erysipelas can be difficult to definitively diagnose. Arthritis and lameness, coupled with postmortem presence of vegetative valvular endocarditis, can support a presumptive diagnosis of chronic erysipelas. However, these lesions can be caused by other infectious agents. Positive culture of valvular vegetations or demonstration of E rhusiopathiae DNA in the lesions by PCR assay is definitive for chronic erysipelas.
Serological tests cannot reliably confirm an erysipelas diagnosis; however, they can help determine previous exposure or success of vaccination protocols, because antibody titers should increase after vaccination. For this purpose, ELISAs and complement fixation tests are available in selected laboratories.
Differential diagnoses of erysipelas include conditions that can precipitate gross lesions suggestive of acute septicemia:
Septicemic salmonellosis due to infection by Salmonella enterica serotype Choleraesuis, classical swine fever due to pestivirus infection, and septicemia and endocarditis due to Streptococcus suis infection should be considered, given the similarity of lesions.
Similar skin lesions can be found with porcine dermatitis and nephropathy syndrome (caused by porcine circovirus) or infection with classical swine fever or A suis infection.
Glässer disease (caused by Glaesserella parasuis [formerly Haemophilus parasuis] infection) and Mycoplasma hyosynoviae infection can precipitate similar changes in synovial tissues and joints of affected pigs.
Treatment of Swine Erysipelas
Antimicrobials, particularly penicillin
E rhusiopathiae is susceptible to penicillin, and early treatment generally leads to recoveryfrom erysipelas. Ideally, affected pigs should be treated at 12-hour intervals for a minimum of 3 days with penicillin G procaine injection; however, longer durations of treatment might be necessary to resolve severe infections.
Economically, penicillin is the best choice for antimicrobial treatment of erysipelas, but ampicillin and ceftiofur also yield satisfactory results in acute cases. When injecting large numbers of affected pigs is impractical, tetracyclines delivered in feed or water can be useful; however, resistance to tetracycline is occasionally reported.
Fever associated with acute erysipelas can be managed with NSAIDs such as flunixin meglumine or with aspirin (not approved for use in animals in the US) in the water. Erysipelas antiserum is described as an effective adjunct to antimicrobial treatment in acute outbreaks, but it is not commonly available.
Treatment of chronic erysipelas is usually ineffectual and not cost effective.
Prevention of Swine Erysipelas
Vaccination against E rhusiopathiae is very effective in controlling disease outbreaks on swine farms and should be encouraged. Vaccination might not be as effective in preventing chronic arthritis, however. Cessation of vaccination on some farms has been linked to disease outbreaks.
Injectable bacterins and live attenuated vaccines delivered via the water are available and provide extended duration of immunity. Optimal timing of vaccination varies from farm to farm. When E rhusiopathiae is endemic in the production environment, vaccination should precede anticipated outbreaks.
Pigs susceptible to E rhusiopathiae infection can be vaccinated before weaning, at weaning, or several weeks after weaning. Males and females selected for addition to the breeding herd should be administered a booster 3–5 weeks later. Thereafter, breeding stock should be vaccinated twice yearly.
Vaccines should not be administered to animals undergoing antimicrobial treatment, because antimicrobials can interfere with the subsequent immune response to the vaccine.
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Vaccination failures can result from management stresses that compromise the immune system of vaccinated pigs. The use of live vaccines can lead to disease, particularly chronic erysipelas.
Antigenic differences between serotypes in vaccines and serotypes circulating on farms could also result in incomplete immunity and disease outbreaks. Such events are rare, however, because there is thought to be good cross-protection among the major E rhusiopathiae strains that infect pigs.
In addition to vaccination, attention to sanitation and hygiene and elimination of pigs with clinical signs suggestive of erysipelas infection are other viable methods that can help control the disease on swine farms.
Key Points
Erysipelas in swine is caused primarily by Erysipelothrix rhusiopathiae and has acute, subacute, and chronic manifestations.
Common clinical signs include characteristic diamond-shaped skin lesions, diffuse erythema, septicemia, and/or arthritis.
Pigs are often healthy carriers of E rhusiopathiae. Routine vaccination is effective at preventing acute disease, including animal losses and abattoir condemnations.
For More Information
Erysipelas. The Pig Site.
Erysipelas. UK National Animal Disease Information Service (NADIS).
Swine Erysipelas. New South Wales Government, Department of Primary Industries.
Also see pet owner content regarding erysipelas in potbellied pigs.
