Hog Cholera
Collier's New Encyclopedia (1921)
also known as Swine Fever, a malady affecting hogs, of which the chief symptoms include excessive diarrhea, purple coloring of the skin, lack of appetite, general irritation and inactivity. The virus has been located and is filterable, and is usually conveyed by the water supply. The seat of the disease is in the lungs and intestines and there is much inflammation. The percentage of loss from this disease is very large. There are different varieties of the disease, and two kindred maladies, hog cholera and swine plague, often set up a complication in the same hog. Physicians, however, have differentiated between the two, the former usually attacking the intestines, and the latter usually attacking the lungs. The principal symptom in hog cholera is in the discoloration of the skin; in the other the animal usually suffers from a continual cough. Very often the disease cannot be correctly diagnosed till after death, when the character is indicated by the lesions in the lungs, the intestinal canal or abdominal lymph glands. The disease is contagious and the methods of counteracting it when it affects a herd have to be drastic. The affected hogs have to be segregated, and the pens and surroundings in which they have been confined have to be burnt. Even the ground has to be put into disuse, and the bacilli must be destroyed by putting it into a state of cultivation if it is intended again to use it as a hog yard. The water has to be carefully examined, and the pens kept clean and occasionally whitewashed. Just as there are varieties in the malady so there are degrees in its virulence. In serious cases the hog may die at the end of a couple of days. In a less serious case the animal may continue sick for a period of about five weeks. Hogs have been successfully immunized. The most successful method has been to inject the immune serum into one side and blood from a hog sick with the malady into the other. Tonics containing sodium salts and sulphur have also had good effects.
What Has Changed in the Last Century
Collier's in 1921 could say only that "the virus has been located and is filterable"; it is now known to be a pestivirus of the family Flaviviridae, a relative of bovine viral diarrhoea virus, and the disease is generally called classical swine fever rather than hog cholera. The 1921 confusion with "swine plague" has been resolved: that condition is a bacterial pneumonia (Pasteurella), not a variety of the same malady. The serum-and-virus immunisation Collier's praised was itself a source of new outbreaks and was banned in the United States in 1969; safer attenuated vaccines and slaughter of infected herds allowed the US to declare itself free of the disease in 1978. It remains a major problem in parts of Asia, and European outbreaks such as the Dutch epidemic of 1997-98 have led to the culling of millions of pigs.
Written for this edition, 2026.