By Dr Edgar Ortmann, Howick Veterinary Clinic
Erysipelas is a peracute, acute, subacute or chronic infectious disease of pigs caused by Erysipelothrix rhusiopathiae. The peracute or acute forms manifest as an often fatal septicaemia. The common name “Diamond Skin Disease” is derived from the subacute form, which is characterised by large, roughly diamond-shaped, slightly raised, well-demarcated, purplish-red patches on the skin. Pigs suffering from the chronic form of the disease are usually unthrifty and may have vegetative valvular endocarditis and/or chronic polyarthritis.
In pigs, erysipelas can result in reduced production due to mortality, unthriftiness and increased condemnations at slaughter.
Erysipelas can occur in pigs kept under a variety of conditions and, unlike most of the currently important diseases of pigs, is not associated with intensification of production. Sporadic outbreaks in pigs occur periodically in South Africa.
Other susceptible species are humans, cattle, sheep, horses, white mice, pigeons, turkeys and several other species of birds, but the disease is probably only important in pigs, sheep and turkeys.
Pigs of all ages may contract the disease. It has been suggested that pigs aged between two months and one year, and pregnant sows, are most susceptible. In a herd, a large number of pigs may be affected by the acute septicaemic disease within a short time, or only occasional sporadic cases may occur.
Most infections are acquired from ingestion of food, soil and faeces contaminated with E. rhusiopathiae. Transmission may also occur via bites of infected flies or by contamination of skin wounds.
Under natural conditions, E. rhurhusiopathiae is readily spread by diseased or subclinically infected carrier pigs. All pigs should be considered potential carriers, as the bacterium may be recovered from the tonsils, gastrointestinal tract, gall bladder or faeces of healthy, immune pigs. Recrudescence of infection may occur when these pigs are stressed, with subsequent spread of infection to other pigs.
Other possible sources of thesiosiopathiae is readily spread by diseased or subclinically infected carrier pigs. Other possible sources of the organism are swill, slaughter-house offal, contaminated water and soil, and stable manure. The organism can be spread by slurry to cultivated lands, where it can survive for two to three weeks. Wild birds and rodents have also been incriminated as possible carriers of infection, as they may harbour the bacterium in their gastrointestinal tract.
Erysipelothrix rhusiopathiae may persist indefinitely in clinically healthy pigs, in pigs that have recovered from the disease, or in pigs suffering from chronic arthritis. However, isolation of organisms from chronic lesions or arthritis and endocarditis may be difficult.
Sudden changes in the weather, such as excessively hot or humid weather conditions, overfeeding (particularly of protein), poor hygiene, handling, transportation, and high population densities may predispose to outbreaks of erysipelas.It is precisely this type of weather that KwaZulu-Natal has been experiencing in recent months and numerous cases of erysipelas have been recorded on a number of piggeries.
However, sporadic cases are seen at abattoirs from time to time, when pigs are left to stand over for more than 24 hours. This has sometimes been the case during union strikes, mechanical breakdowns or mixing of pigs a few days before slaughter. These pigs are probably carrying the bacteria on their tonsils or in the intestines without any symptoms. Due to the stress of mixing, transportation and lack of feed intake, the disease breaks out within one to seven days, which is the incubation period.
It stands to reason that the source of infection can also be the lairage at abattoirs especially if these facilities are not disinfected between batches.No pigs should be left to stand over for more than 24 hours at any abattoir because erysipelas is likely to break out under these circumstances.
Producers are therefore warned to ensure that pigs are not stressed unnecessarily before dispatch to the abattoir and to liaise with abattoir personnel with regard to the timeous slaughter of the pigs. Once the producer has delivered the pigs to the abattoir, it is the abattoir’s responsibility to ensure that the pigs are cared for as humanely as possible and not to let them stand over for more than a day. If this should happen, as a result of some unforeseen circumstance, the pigs should be adequately fed and slaughtered as soon as possible. Abattoirs could be held responsible for any losses caused by erysipelas outbreaks if the above conditions are not met.
The accompanying pictures were taken at an abattoir. The producer had seven carcasses condemned after erysipelas was diagnosed at slaughter. The pigs were only slaughtered at the abattoir 3 days after they arrived due to a worker strike.