R. L. Wood

“ Although neuraminidase activity may be largely responsible for the pathogenicity of E. rhusiopathiae, it does not explain virulence, which is the ability of an infectious agent to overcome the host's defenses and initiate the pathologic process. ”

“ Chronic SE Information on the pathogenesis of chronic SE is derived primarily from studies on development of the arthritic lesion, which has stimulated interest because of its apparent similarity to the lesion of rheumatoid arthritis of humans. ”

“ EPIDEMIOLOGY Sources of Infection The most important reservoir of E. rhusiopathiae is probably the domestic pig. It is estimated that 30-50% of apparently healthy or convalescent swine harbor the organism in their tonsils and other lymphoid tissues. These carriers can discharge the organism in their feces or oronasal secretions, creating an important source of infection. Swine affected with acute erysipelas shed E. rhusiopathiae profusely in feces, urine, saliva, and nasal secretions. ”

“ Specific antibodies to the organism have been detected in synovial fluid of chronically arthritic joints and apparently are produced locally by plasma cells in the synovial tissue, which can assume a lymphoid function. It is not known whether the chronicity of the joint lesion is maintained entirely by specific immune reactions against E. rhusiopathiae antigen or whether superimposed autoimmune reactions are involved.
A preponderance of evidence exists to indicate that erysipelatous arthritis is initiated by active infection of the joint. ”

“ Swine erysipelas (SE) or its equivalent in other languages _Schweinerotlauf, vlekziekte, rouget du porc, mal rossino, entrace eresipelatoso, rozyca, and erisipela del cerdo_is a disease caused by the bacterium Erysipelothrix rhusiopathiae (Sneath et al. 1986) and manifested by acute or subacute septicemia and chronic proliferative lesions. The disease is worldwide in distribution and is of economic importance throughout Europe, Asia, and the Australian and American continents. ”

“ Mild synovitis and arthritis have been induced in rabbits and rats by massive intravenous or intraarticular injections with nonliving whole cells or fractions of the organism (White et al. 1975; Hermanns et al. 1982) , but the lesions were not as severe as those typically caused by infection. White et al. (1975) suggested that the mild response induced by such antigens may predispose the joint to infection during a subsequent transient septicemia. ”

“ There is evidence that the bacteria do not entirely disappear from chronically affected joints, and the longterm progressive lesion may occur in response to the continued presence of either whole bacterial cells or their antigens. Schulz et al. (1977) reported that living E. rhusiopathiae was occasionally isolated from such joints for up to 2 years. Furthermore, they stated that E. rhusiopathiae antigen could be detected by immunofluorescence and whole or fragmented bacteria could be seen with the electron microscope in culturally negative joints. ”

“ Development of immunity in vaccinated swine may be adversely affected by such environmental factors as overheating or poor nutrition.
A serious deficiency of SE vaccination is its inability to prevent the chronic form. Most investigators agree that vaccination has little effect on the incidence of arthritis caused by E. rhusiopathiae, although this observation is difficult to evaluate in the field, since SE vaccination is not universally practiced in the United States. It is possible that vaccination reduces the overall prevalence of arthritis by reducing the prevalence of acute erysipelas. ”

“ Specific antibody activity against E. rhusiopathiae neuraminidase has been demonstrated in sera of swine with chronic SE, in commercial equine antierysipelas serum, and in serum of rabbits hyperimmunized with a preparation of neuraminidase from the organism. This latter preparation also induced a low level of protection in mice to E. rhusiopathiae infection. Neuraminidase is not a toxin; it must be produced in large amounts to be pathogenically active. It can act on substrates in cell membranes throughout the body, and no doubt its activity reaches high levels in an acute septicemia. ”

“ Bacteriologic Diagnosis Isolation of E. rhusiopathiae from the acutely affected animal provides a definite laboratory diagnosis of SE. Hemoculture is a useful diagnostic aid in living animals, but specimens should be taken from several affected animals in the herd, as the presence of the organism in the blood of an individual may be inconstant. At necropsy of a pig that has died in the acute phase, the organism is easily cultured from a variety of body organs (heart, lungs, liver, spleen, kidneys, joints) . ”

“ The organism can readily gain access to the body through the palatine tonsils or other lymphoid tissue in the wall of the digestive tract, but entrance is probably not limited to these areas.
Natural infection no doubt can result from infected skin wounds, which may be concealed or too small to be readily noticeable. ”

“ An agglutination test involving the use of growing culture as antigen was developed by Wellmann (1955) . In this test, called the Wachstumsprobe or growthagglutination test, a culture of E. rhusiopathiae growing in liquid medium in the presence of sterile test serum agglutinates if sufficient specific antibody is present.
No serologic test has proved useful for routine diagnosis of acute infection or for differentiation between immune and susceptible pigs. Serologic diagnosis may have some value in detection of chronic infection, primarily on a herd basis. ”

“ In humans E. rhusiopathiae causes erysipeloid, a local skin lesion that occurs chiefly as an occupational disease of persons engaged in handling and processing meat, poultry, and fish as well as of rendering-plant workers, veterinarians, game handlers, leather workers, laboratory workers, and the like. The organism occasionally is isolated from cases of endocarditis in humans and rarely causes acute septicemic disease. ”

“ Synovitis and arthritis of chronic SE in a hock joint 8 weeks after exposure to E. rhusiopathiae. Note hyperemia and proliferation of synovial tissue. (Courtesy National Animal Disease Center, Ames, Iowa) . Vegetative endocarditis consists of proliferative granular growths on the heart valves and may be accompanied by lesions resulting from cardiac insufficiency. Other internal organs may show chronic inflammatory changes such as infarcts of kidneys and spleen. ”

“ Vascular lesions can be seen in the heart, kidney, lung, liver, nervous system, skeletal muscle, and synovial membranes. Cellular response to infection by E. rhusiopathiae consists predominantly of mononuclear leukocytes and macrophages. Neutrophils may appear but do not predominate. Purulent lesions are not characteristic of E. rhusiopathiae infection.
Affected lymph nodes usually show acute hyperplastic lymphadenitis, with hyperemia and hemorrhage. In some nodes there may be evidence of thrombosis and necrosis of small blood vessels and capillaries. ”

“ Culture of E. rhusiopathiae from tissue specimens is relatively simple and requires only basic laboratory equipment and culture media such as tryptose or meat infusion media with or without blood or serum added. Care should be taken to avoid accidental skin infection, as the organism is pathogenic for humans. ”

“ Attenuated vaccines should not be given to swine being treated with antibiotics to which E. rhusiopathiae is sensitive. Antibiotic treatment should be discontinued at least 8-10 days before vaccination.
Attenuated vaccines are usually given by injection or administered orally in drinking water. Some manufacturers provide a product that can be given either way. In some parts of Europe and the former Soviet Union, vaccination by aerosol has been practiced. Elaborate equipment for generating and distributing the aerosol is necessary. ”

“ Good sanitation is important in general herd management and is essential following the cessation of an outbreak. Walls and floors should be cleaned and disinfected. Phenolic, alkali, hypochlorite, or quaternary ammonium disinfectants are effective against the organism but must be applied to clean surfaces.
Immunization A variety of biological products have been produced for the purpose of conferring immunity to SE in swine. The simultaneous or serum-culture method of immunization was introduced in 1893 and consists of concomitant injections of virulent culture and antiserum. ”

“ Chronic SE Chronic SE may follow acute or subacute disease or subclinical infection and is characterized most commonly by signs of arthritis. Signs of cardiac insufficiency may be seen occasionally and will be most noticeable following exertion, sometimes causing sudden death. Chronic arthritis results in joints that show various degrees of stiffness and enlargement, sometimes as early as 3 weeks after infection. Interference with locomotion ranges from a slight limp to complete refusal to put weight on the limb, depending upon the extent of damage. ”

“ Naturally acquired active immunity is induced by previous infection with E. rhusiopathiae. It is well known that immunity to acute SE follows clinical disease. Less well recognized is the immunity that can be induced by organisms of low virulence, which are capable of causing mild unnoticed subacute disease or subclinical infection.
PREDISPOSING FACTORS. SE can occur with other swine diseases, but the significance of preexisting infectious disease as a predisposing factor is uncertain. ”

“ Use of living vaccines leaves open the possibility, however remote, of vaccinated animals becoming carriers and disseminators of the organism, which conceivably could undergo increased virulence through serial passage. There is no experimental evidence, however, that attenuated SE vaccines can regain their virulence and pose a hazard to susceptible swine. ”

“ When attempting to evaluate factors that may be related to the occurrence of SE on the farm, it should be kept in mind that a variety of stimuli in the animal's total environment can affect the level of susceptibility existing at any given time. ”

“ GROWTH CHARACTERISTICS. Growth of E. rhusiopathiae at 37°C in a nutrient broth appears at 24 hours as a faint turbidity with no odor or pellicle. Shaking typically reveals a momentary appearance of rolling clouds. Slight sedimentation will be seen after 36-48 hours of incubation. Growth is much heavier in broth enriched with serum. In gelatin stabs incubated at 22ûC for 4-8 days, growth of the organism radiates out from the stab in all directions, resembling a test-tube brush. ”

“ For maximum effectiveness the serum must be given early in the course of the disease. The recommended therapeutic dose, given subcutaneously, varies from 5 to 10 mL for pigs weighing less than 50 pounds (23 kg) to 20-40 mL for pigs weighing more than 100 pounds (45 kg) .
It is generally accepted that the treatment of choice for acute erysipelas is administration of penicillin. E. rhusiopathiae is highly sensitive to this antibiotic, and treatment early in an acute outbreak usually results in dramatic response within 24-36 hours. ”

“ It is typically made from selected strains of serovar 2 that produce a soluble immunogenic product when grown in a complex liquid medium containing serum. This substance, most of which is released into the medium, has been described as a glyco-lipoprotein (White and Verwey 1970) . It is considered by most investigators to be a necessary ingredient for stimulation of immunity by the bacterin. ”

“ On the light-skinned pig they can be seen as small, light pink to dark purple areas that usually become raised, are firm to the touch, and in most instances are easily palpated. In animals with dark-pigmented skin, one must rely mainly on palpation, although the weltlike lesions may be detected by observing raised areas in the hair coat. ”

“ The entire herd may also be given antiserum if the outbreak is very severe. As an alternative, long-acting penicillin may be given in severe outbreaks, and procaine penicillin G in less severe cases. The use of antiserum for treatment of suckling pigs is a fairly common practice. Initiation of a vaccination program in previously unvaccinated herds where outbreaks occur is strongly recommended. ”

“ Infrequently, severely affected pigs do not die, and skin necrosis may follow the severe cutaneous lesions. The areas of necrotic skin are dark, dry, and firm and eventually become separated from the healing underlying tissue. Affected areas, particularly the ears and tail, will eventually slough. Healing may require many weeks as a result of secondary infection.
Subacute SE Subacute SE includes signs that are less severe in their manifestations than the acute form. The animals do not appear as sick; temperatures may not be as high or may not persist as long; appetite may be unaffected ”

“ Those visibly sick will have temperatures of 104–108 ̊F (40–42 ̊C) and over, and those with the higher temperatures may show signs of chilling. Some pigs may appear normal and yet have temperatures of around 106 ̊F (41 ̊C) . In surviving pigs, temperatures usually return to normal within 5–7 days.
Affected animals withdraw from the herd and will be found lying down. When approached, they resent being disturbed but usually will get up and move away. This usually is accompanied by squealing; when walking, they show a stiff, stilted gait. ”

“ The proliferating tissue also may extend across the surface of articular cartilage, forming a pannus that leads to destruction of the articular surface and eventually to fibrosis and ankylosis of the joint. ”

“ The liver usually is congested. The appearance of the spleen is of particular note, for it may be congested and markedly enlarged, particularly in animals affected for several days. Petechial hemorrhages may be present in the cortex of the kidneys. ”

“ Strains that do not possess the specific antigen are referred to as serovar N.
Immunizing antigen is discussed in the section on prevention.
Biological Characteristics GROWTH REQUIREMENTS. E. rhusiopathiae is facultatively anaerobic; some strains grow better in an atmosphere of reduced oxygen containing 5–10% carbon dioxide. The organism will grow at temperatures of 5–42 ̊C. Optimum growth occurs at 30–37 ̊C and at a pH range of 7.4–7.8. Growth is enhanced by serum, glucose, protein hydrolysates, or surfactants such as Tween-80. The organism is fastidious ”

“ Light pink to light purplish-red lesions are characteristic of acute nonfatal SE, whereas angry dark purplish-red lesions usually precede death of the animal. In acute fatal disease, extensive dark purplish discoloration often occurs over the belly, ears, tail, posterior aspect of the thighs, and jowls. ”