RICHARD D. SHUMAN AND O. L. OSTEEN.
SWINE erysipelas is present in the United States wherever hogs are raised. It is worst in regions, like the Midwest, where the hog population is dense. It is serious in Europe, parts of Asia, and North America.
R. Koch, F. A. J. Loffler, L. Pasteur, and M. L. Thuillier all of whom are famous in scientific history are associated with the discovery of the causative organism of erysipelas in the 1880's. Previously swine erysipelas was confused with anthrax. The work of Theobold Smith, in the former Bureau of Animal Industry, showed that the disease was present in this country before 1900. G. T. Creech, also of the Bureau of Animal Industry, in 1921 demonstrated the relationship of diamond skin disease (a clinical form of swine erysipelas) and the causative agent of erysipelas. The disease caused little trouble until the 1930's, when A. A. Fosterman, a veterinarian in South Dakota, directed attention to its acute aspect. Swine erysipelas has since become one of the most serious hazards of the swine industry.
The causative agent is a bacterium, Erysipelothrix rhusiopathiae. It is a hardy organism and can live in dead animal tissue and decaying matter. It can resist the effects of pickling, smoking, freezing, and drying of meats for long periods. It is rather sensitive to heat, however, and is killed at temperatures necessary to cook the chop or roast well.
The organism is considered to live in the soil as a saprophyte and can multiply under favorable conditions of moisture and in soil rich in humus.
Disinfectants commonly available and used according to directions will destroy it.
The organisms have been found in all parts of the world and in a wide variety of animals, birds, fish, and insects. Of major economic importance is the effect of the disease in swine, turkeys, and sheep.
Infection of people is not uncommon (erysipeloid). It is an occupational hazard of veterinarians, persons who handle fresh meat and meat products, and commercial handlers of marine fish. Home butchering and processing of pork also has been the source of infection of people.
Probably the chief source of swine erysipelas infection is the organism present in the soil. A saprophyte, the organism can live on dead and decaying organic material it does not require a living animal to maintain itself. Perhaps it has always been present as a soil organism.
Another source is the animal carrier. The organism can exist in the tonsils and the lymphoid tissue of the intestinal tract of apparently normal swine.
Hogs that become affected with swine erysipelas may or may not show actual clinical symptoms of the disease, but in each instance it is possible for the organism to be eliminated from the animal's body through the feces and urine. Hogs that die from the disease and remain undetected in the field can contaminate the soil and can be the source of an outbreak when eaten by other hogs.
Very likely birds and other wildlife that carry the organism contaminate the soil in the hog lots with their droppings.
Animals become infected through contact. with the soil that contains the organism by ingestion of contaminated feed and water and by infection of wounds. Fighting may lead to wounds of the lips, face, and shoulders. Sharp rocks, glass, and other objects cause wounds in and around the claws or lips while rooting. Protruding nails or broken boards and pieces of wire fence also can cause tears and breaks of the skin.
One sick hog can cause an outbreak of the disease through its elimination of the organism in its dung and urine.
Because the organism can be found also in the circulating blood of an infected animal, there is a possibility that bloodsucking insects may transmit the disease to other hogs. G. Wellmann of Germany has shown this to be possible by experimentally transmitting the disease with biting flies.
SWINE ERYSIPELAS has a peculiar behavior: Why did the disease apparently lie dormant for many years and then become a menace in the early 1930's? Why does it show itself on a farm for several seasons and then seemingly disappear? Why do some areas remain known as erysipelas areas? Some outbreaks years ago could have been confused with hog cholera (they can occur at the same time), but the real reason is not known.
The other peculiarities can be explained on the basis of what is known to be possible. We have known for a long time that the causative agent can be one of relatively low virulence or one of great virulency: Because it is not always the same, its ability to produce disease can vary a lot. It is possible that we may even be dealing with different strains or variants of the same organism. At any rate, since the infectiveness of an organism can be increased or lowered by artificial means in the laboratory, it is very likely that such external factors as climate and soil conditions also can alter its disease-producing ability. This could then be demonstrated on the farm by either a high incidence of disease, with many dead animals, or a low incidence, with just a few sick ones in the herd.
Swine erysipelas also can be present in a herd in such a mild form that it remains unnoticed. Many animals therefore become immune through natural infection. On a farm where this condition occurs, one could easily conclude that erysipelas died out or disappeared, although actually it was still there. All that would be needed to change this situation into an outbreak would be an increased virulency of the organism and the presence of susceptible hogs.
THE CLINICAL SYMPTOMS of swine erysipelas are classed as acute, subacute, and chronic.
Acute swine erysipelas is characterized by its sudden onset. Many animals in the herd may be affected at once. Only a few may be visibly sick, but a number of others may run temperatures of over 104 . Sick pigs tend to stay where they are bedded, yet at the same time their eyes give an impression of alertness. If stirred up and forced to move, they will protest with squeals as though it were painful to put weight on their feet. Sometimes the animals may show a peculiar stilty and stiff gait, or they may stand with their feet under them, and head hanging down. so that the back line has an arched appearance. The attitude becomes one of dejection or depression. Left alone, they quickly make themselves as comfortable as possible in the bedding again. Most animals show little desire for food or go off feed altogether. A not uncommon symptom is nausea and vomiting. Some animals breathe with difficulty and have a husky cough. If there is any change in the feces, it is more likely to be dry and reduced in quantity. Several of the pigs may die suddenly; others will be obviously sick, as we described, and a few may die in 7 or 10 days.
During the acute phase, many hogs may develop what is called diamond skin disease, or the urticarial form of swine erysipelas. This phase is marked by light-pink to dark-purple areas on the skin that usually become raised and firm to the touch and in most instances have clearly defined borders. The shape is quite characteristic when seen or felt, because the outline of the skin lesion assumes a square, a rectangular, or a rhomboidal geometric pattern. The lesions might join and cover quite a large area of the skin. Although the lesions are best seen on a light-skinned animal, they can be felt (but are easily overlooked in either case, particularly if they are not too numerous) on animals with darker skins. The number of "diamond skin" lesions can vary from one to so many that it would be hard to count them.
The skin lesions may disappear in several days, or they may become areas of dry, firm, darkened, scabby, dead skin and under tissue. These areas of dead skin will eventually fall off, leaving an ugly scarred area. It is here that one will also see loss of tips of the ears and tail. Secondary infection usually takes place during this stage and prolongs the healing process. Although the mortality rate of hogs showing diamond skin disease may not be particularly high, animals that have it will probably be affected with arthritis and the owner will be left with a number of pigs, which are unprofitable to feed out.