Erysipelothrix rhusiopathiae is a significant opportunistic bacterial pathogen of swine, turkeys, and sheep. It is distributed worldwide and has also been isolated from cattle, horses, dogs, cats, mice, rats, fresh and saltwater fish, domestic poultry, marine mammals, and a variety of wild birds and mammals.
In turkeys, cyanotic skin lesions manifest most obviously as a "blue comb." Other sequelae of E rhusiopathiae infection in this species include muscle petechiae and hemorrhaging, sudden deaths, and male infertility. Incidence of erysipelas in poultry appears to be increasing in association with the change to cageless production systems, particularly in Europe.
E rhusiopathiae infection causes sporadic but serious disease in captive marine mammals. Newly described manifestations of E rhusiopathiae infection also include large-scale mortality events in northern wild ungulates. Erysipelothrix spp have also recently been described as a cause of low to moderate mortality in ornamental fish.
As a zoonosis, it manifests as erysipeloid, a condition characterized by localized skin infections and cellulitis. This may develop in people who work with infected animals, infected carcasses, or infected animal byproducts. Other, less common manifestations of E rhusiopathiae infection in humans include a generalized cutaneous form and a septicemic form that may involve endocarditis.
Postdipping lameness is characterized by severe lameness that results from infection caused by the penetration of E rhusiopathiae through skin abrasions in the hoof. With time and repeated use, sheep dipping solutions become contaminated with E rhusiopathiae and other bacteria. Discarding heavily contaminated dips is the best way to prevent infection and the associated lameness. Because dipping is now rarely used as a means to control external parasites, this condition is now rare.
The genus Erysipelothrix is subdivided into two major species: E rhusiopathiae and E tonsillarum. Other species (ie.,E species 1, E species 2 , and E inopinata) are less well-characterized and are rarely associated with clinical disease. At least 28 different serotypes of Erysipelothrix spp are recognized, and pigs are considered to be susceptible to at least 15. Field cases of swine erysipelas are predominantly caused by E rhusiopathiae serotypes 1a, 1b, or 2.
The bacterium can survive in the soil for up to 5 weeks; however, soil is not an effective growth medium, and the organism is unable to survive for extended periods of time in the environment. Soil and surface water contamination represent routes of exposure. Asymptomatic carriers are the usual source of infectious organisms, but the bacteria may also be introduced to animal production units by surface water runoff, wild mammals, wild birds, pets, and biting insects. E rhusiopathiae has food safety implications, because it can survive for several months in animal tissues such as frozen or chilled pork, cured and smoked ham, and feed byproducts such as dried blood.
E rhusiopathiae is a nonmotile, gram-positive, facultative anaerobic bacillus. It is catalase negative, coagulase positive, oxidase negative, resistant to high salt concentrations, and produces H2S on triple sugar iron media. Colonies of E rhusiopathiae are either smooth or rough, with rough colonies being slightly larger, with irregular edges. On agar media, colonies are clear, circular, nonhemolytic, and very small (0.1–1.5 mm in diameter) after 24 hours of incubation. They increase in size after 48 hours and tend to develop a pale blue opacity. A zone of incomplete hemolysis also becomes evident around colonies.
The organism is very hardy and can survive and grow in a wide range of pH and environmental temperatures. E rhusiopathiae has demonstrated the ability to resist the action of several classes of disinfectants used in animal production units, including alcohols, aldehydes, oxidizing agents, and phenols. Classes of disinfectants and/or compounds considered to effectively inactivate E rhusiopathiae include hypochlorites (bleach) and caustic soda (lye; NaOH). Regardless of which disinfectant is used, removing organic matter by thorough cleaning before application will improve effectiveness. The organism is sensitive to the beta-lactam (penicillin, ampicillin), cephalosporin (ceftiofur), and tetracycline classes of antibiotics and is resistant to sulfonamides and vancomycin.