Age affected: All ages, human risk.
Causes: Bacterium - Erysipelothrix rhusiopathiae.
Effects: Fever, sudden death, red skin ‘diamonds’, blue extremities, lameness.
Swine erysipelas is caused by the bacterium Erysipelothrix rhusiopathiae and its very close relative, E. tonsillarum. They are slender rod-shaped bacteria and form delicate colonies after 24-48 hours in culture. The two species cannot be distinguished easily in culture, but the antibodies to which they give rise demonstrate the existence of at least 28 serotypes of the two organisms. When the two species were separated, some serotypes (particularly serotypes 3, 7 and 10) were found to belong to E. tonsillarum.
The organisms survive for months or years in animal tissue kept cool or frozen, are rapidly destroyed by heat and are extremely sensitive to penicillin. Erysipelas organisms can enter the body through the tonsil, gut or through cuts and scratches on the skin. Within 1-7 days they give rise to clinical disease. Invasion is followed by multiplication in the blood stream and by fever which can cause abortion in pregnant animals. The organisms localise in the skin, the joints or the heart valves to cause skin lesions, arthritis and endocarditis. Antibody produced to the organism causing the disease cross protects against infection with most strains of the species concerned.
Mode of transmission
Erysipelas bacteria infect pigs orally via the gut and tonsil in most cases but can penetrate skin through abrasions. Infected animals shed the organism in faeces and urine and infection may be transmitted directly from pig to pig, particularly within a pen or along a drainage channel. The organisms survive outside the body for up to 35 days in soil and 7 days in slurry but do not multiply there. It infects birds and other mammals, so some infections can result from contact with organisms in slurry and soil deposited by pigs or by a range of birds and mammals.
Infected pigs die suddenly or are dull and collapse with a high temperature (41.1-42.8°C, 106-109°F) and a scarlet flush on the skin. In gilts, fattening pigs and young boars, inappetence and high fever of 41.1-42.2°C, 106-109°F is common and there may be flushing or blotching of the skin and ears. Affected animals are dull and reluctant to move. Diamond skin lesions occur within 48 hours of the onset of clinical signs and can be felt as raised patches along the back or neck but rapidly become purplish-red. Abortion may occur in sows, temporary infertility occurs in boars and served sows may return. Affected animals may recover completely, but the skin lesions may become necrotic (die), turn black and slough. The tips of the ears may also be lost. Arthritis of the elbow, hip, back, stifle and knee joints may develop and cause lameness. Affected joints become hot and painful to the touch but become firm after 2-3 weeks. The heart valves may develop lesions and give rise to a murmur. Sudden death or signs of congestive heart failure may occur later.
Erysipelas should be considered if fever of 41.1°C, 106°F occurs in finishing or adult pigs which have gone off their feed and show no respiratory signs, particularly in hot, humid weather. The development of the characteristic skin lesions in one of a group of affected animals confirms the diagnosis. Erysipelas should be considered in cases where lameness and fever occur together and also when sows at difficult farrowings are found to have fever. Serological (blood antibody) diagnosis is possible, but false negative results can occur if the test does not include the Erysipelas strain that is causing the infection.
Where pigs have died, post-mortem findings of purplish discolouration of the skin and cyanosis of the ears and the diamond skin lesions may be present. The spleen may be enlarged, lymph nodes haemorrhagic and swollen, and there may be spots of blood (petechiae) on the kidney, pleura, peritoneum and on the heart. Chronically affected pigs may have blackened skin lesions or enlarged joints with arthritis. The heart may be enlarged and large granular vegetations may occur on the heart valves. The organisms can be cultured from the blood and from most parts of the carcase in acute disease and PCR testing can confirm their presence. In chronic disease, they may only be recoverable from the joints or skin lesions.
Treatment and prevention
Injections of penicillin are used for the treatment of erysipelas and the response is normally rapid. It is advisable to give 2 or 3 daily injections to prevent relapse or the persistence of the organism to give chronic infection. As the erysipelas organisms are widespread in the environment and are carried by clinically normal pigs, exposure cannot be prevented. However, it is advisable to clean out and disinfect the pens of affected animals as high concentrations of virulent bacteria may be present.
The disease is usually prevented in the short term by injecting animals in contact with cases with long-acting penicillin. Vaccination is commonly employed to prevent clinical swine erysipelas. Most commercially available vaccines are formolised whole cultures and include an adjuvant. Vaccination is normally practised in recently weaned pigs (finisher protection) and in gilts or sows before service to prevent conception problems. Immunity lasts for 6 months and regular re-vaccination should be practised. The vaccination of pregnant animals is not recommended with some dead vaccines and all live ones. All boars should be vaccinated at 6 monthly intervals. Vaccines containing serotypes 2 and 10 protect against both E. rhusiopathiae and E. tonsillarum.
Erysipelas organisms can infect humans, usually producing a local lesion following contamination of cuts and abrasions present during post mortem examination of cases. The disease is a cause of condemnation of carcases at meat inspection.