By Angela E. Pillatzki, DVM, MS, Dipl ACVP, South Dakota State University
Erysipelothrix rhusiopathiae causes a disease in pigs known as erysipelas, which can manifest in acute, subacute or chronic clinical forms. This organism, E. rhusiopathiae, is a facultative, Gram-positive bacillus and it has global distribution. It can also cause systemic clinical disease in other animals including farmed turkeys, chickens, ducks and emus, and polyarthritis in sheep and lambs6.
This organism also causes clinical disease in humans, a condition called erysipeloid. Erysipeloid most commonly manifests as a localized, painful skin infection, and it usually affects the fingers and hands7. E. rhusiopathiae causes the greatest economic losses to the turkey and swine industries, and swine erysipelas, specifically, has caused economic losses throughout North America, Europe, Asia and Australia7. Increased mortality, treatment costs and vaccination costs, and slower growth of pigs with clinical disease are the factors associated with economic losses due to swine erysipelas7. Recently, several outbreaks of swine erysipelas have been reported in the United States2, China8, Japan5 and the United Kingdom3. These outbreaks may suggest a re-emergence of an economically important swine pathogen that has been documented since the late-19th century and reaching epidemic status in the domestic swine population in the mid-20th century.
It is estimated that approximately 30-50% of healthy pigs carry E. rhusiopathiae in their tonsils and other lymphoid tissues4. These subclinically affected pigs can shed organisms in urine, feces, saliva and nasal secretions, and they are believed to be the source for erysipelas outbreaks4. The primary modes of direct transmission are through oronasal secretions and feces, and indirectly via environmental contamination4. Erysipelothrix spp. can be inactivated by several common disinfectants. However, a combination of deep cleaning and disinfection are required to thoroughly remove organic material, which can harbor the organism4.
Swine erysipelas most commonly occurs in pigs older than 12 weeks of age or in the grow-finish stage of production, or in young, naïve adults. Three clinical forms of swine erysipelas are recognized. The acute form is manifested as sudden death, or rapid onset of high fever, depression and lethargy, reluctance to move and vocalization during movement, painful joints and the characteristic red-purple, raised, square to diamond-shaped, skin lesions. During necropsy, additional but less specific changes such as an enlarged spleen, enlarged and reddened lymph nodes, reddened and somewhat firm lungs, and red pinpoints and streaks throughout the outer portion of the kidneys and the heart muscle, may be observed. The mortality rate in acute swine erysipelas can reach 30-40% in naïve herds. Tissues surrounding affected joints may be loose and expanded by fluid, and joints may contain an increased amount of thin watery and cloudy joint fluid. Joint fluid may also contain thin, delicate strands of inflammatory exudate (cells and protein that accumulate during the process of inflammation).
The subacute form displays similar clinical signs to the acute form, but pigs are less severely affected, and the mortality rate is lower. Fevers are not as high, skin lesions are not as severe or may be absent, and pigs recover faster. Reproductive failure can also occur in both forms with an increased rate of abortions occurring in the acute form. Infertility and an increased rate of mummies or smaller litters can occur with the subacute form of swine erysipelas.
Chronic swine erysipelas can develop in some pigs that seemingly recover from the acute or subacute forms, or in pigs that only develop a very subtle, often undetected, clinical form of disease (subclinical animals). Pigs suffering from chronic erysipelas either develop arthritis or vegetative valvular endocarditis (infection of heart valve), or both. Chronic arthritis is the most economically significant manifestation of the chronic form of this disease because animals become lame, feed intake is reduced and animals lose condition. Affected joints are enlarged and firm. When joints are examined, the synovial membrane (thin and delicate, opaque lining of the non-bone portion of a joint) is often thickened, red or tan colored, and may be nodular. The amount of joint fluid is increased, and the fluid is dark yellow to red, thin and watery and cloudy. Signs of arthritis may appear in animals suffering from the chronic form of erysipelas as soon as three weeks after an initial outbreak in a herd. Animals with vegetative valvular endocarditis may suffer from cardiac dysfunction, and develop respiratory signs due to pulmonary edema, lethargy, cyanosis (a bluish discoloration of the skin), or sudden death. During necropsy, one or more valves of the heart are dark red to tan, thickened and nodular, and have a granular texture. The mitral valve, the heart valve separating the left atrium and ventricle, is most commonly affected.
The clinical signs of acute swine erysipelas can be difficult to differentiate from other systemic bacterial diseases caused by Salmonella cholerasuis, Actinobacillus suis, Actinobacillus pleuropneumoniae, Haemophilus parasuis and Streptococcus suis. The skin lesions of swine erysipelas can also resemble skin lesions observed with porcine dermatitis and nephropathy syndrome, which is caused by porcine circovirus type-2, systemic infection by Actinobacillus suis and classical swine fever. Therefore, definitive diagnosis of infection with Erysipelothrix rhusiopathiae is important for application of effective therapy and prevention strategies. Definitive laboratory diagnosis of swine erysipelas can be achieved by direct culture of E. rhusiopathiae from noncontaminated, diseased tissues (e.g. skin, joint tissues or fluid, heart, spleen, lung, kidney). However, certain conditions such as chronic cases, contaminated tissues, and tissues from animals that had previous treatment with antibiotics can decrease the likelihood of bacterial isolation. Use of enrichment media may aid in the isolation of E. rhusiopathiae in some cases. Other laboratory tests such as immunohistochemistry and polymerase chain reaction are also available. It is important to demonstrate the organism within diseased tissues in order to reach a definitive diagnosis.
Serotyping of Erysipelothrix spp. isolates is also available but is not routinely used for general diagnostic purposes. Field cases of swine erysipelas are predominantly caused by E. rhusiopathiae serotypes 1a, 1b, and 2 worldwide4. Other less common serotypes of E. rhusiopathiae are occasionally associated with less severe disease outbreaks. However in recent years, there have been reports of clinically relevant swine erysipelas caused by several different serotypes (serotype 212, serotypes 7, 10, and 111, serotype 153 and untypeable isolate5). In a situation where commonly effective therapies and preventative measures are not successful, serotyping of E. rhusiopathiae from demonstrated cases of swine erysipelas may be useful.
Swine erysipelas is an economically important disease that may be undergoing a resurgence in the swine industry worldwide. Consultation with a veterinarian and laboratory diagnostic testing are important components to achieving effective treatment, management and prevention strategies.
1. Bender JS, Irwin CK, Shen HG, Schwartz KJ, Opriessnig T. Erysipelothrix spp. genotypes, serotypes, and surface protective antigen types associated with abattoir condemnations. J Vet Diagn Invest 2011; 23:139-142.