Anthrax (Gr., 'a carbuncle'), the name now generally used of a widely-distributed and very destructive disease, most common among sheep and cattle. Besides its practical importance, it has special theoretical interest, because it was the first infectious disease proved to be due to the presence of microscopic vegetable organisms (bacilli; see GERM THEORY), and because it has been more fully studied than any other analogous disease.
Synonyms and Distribution.—Anthrax has received many names; the most important are Splenic Apoplexy, Splenic Fever; as it occurs in man, Malignant Pustule, Woolsorter's Disease; in French, Charbon, Sang de Rata, Mal de Sang; in German, Milzbrand. It occurs in most countries of Europe, especially France, Germany, Austria, and Italy; in Turkey in Asia, Persia, China, South Africa, and South America; in Siberia, chiefly among horses, as Siberian Plague. The Loodiana Fever and Pali Plague of India, and the disease which was very fatal to horses and cattle in the Zulu war, are closely allied, if not identical. The disease of cattle called Black-leg or Quarter Evil, though very similar, is now proved to be distinct from anthrax.
Animals affected.—Cattle and sheep are most commonly attacked by anthrax. Among horses and camels it is also very destructive. Rabbits, hares, mice, guinea-pigs are readily affected, and probably many other herbivorous mammals. It has been found that rats are susceptible to it when fed on vegetables, but not when on animal diet; and probably food has a similar influence in man. Carnivorous animals become affected with difficulty, if at all. Fowls can contract it, but only when their temperature, naturally higher than that of mammals, is artificially reduced.
Symptoms in Animals.—In the most acute (apoplecticiform) cases, the animal falls as if it had received a severe blow, and goes into convulsions; the pulse is quickened, the breathing becomes rapid and laboured, and death follows in a few minutes or hours. In less acute cases, the animal loses its appetite, becomes thirsty and feverish, and often has bloody diarrhoea; may appear to recover, only to have a more severe seizure after a short interval; and in a fatal case dies with great enfeeblement, convulsions, and laboured breathing, usually within two days of the first symptoms.
Occurrence and Symptoms in Man.—Anthrax does not readily attack man, and is very rarely communicated by one human being to another. It occurs in those whose occupations bring them into contact with diseased animals or their hides, wool, &c.—i.e. butchers, farriers, porters, &c. In this country, the source of infection is generally imported wool or hides. Two distinct forms are met with: (1) Internal Anthrax, or Woolsorter's Disease; (2) External Anthrax, or Malignant Pustule. (1) Peculiar cases of rapid fatal illness had long been known to occur in those employed among wool from abroad, especially at and near Bradford, but were first identified with anthrax in 1879. The symptoms are much like those in animals, but less rapid; 'apoplecticiform' cases are very rare, and death usually occurs between the third and seventh day after the first severe symptoms. In such cases the poison is probably inhaled, and enters the blood from the respiratory organs. (2) In External Anthrax, the poison is introduced through an abrasion or wound of the skin. The disease begins as a small red spot, but soon leads to destruction of the portion of skin involved, and inflammation of the surrounding tissues. The affected part now forms a defined hard lump surrounded by a soft swollen area of skin. There is a singular absence of pain and suppuration, which distinguishes it from the ordinary forms of inflammation. Within a few days of the first appearance of this malignant pustule, constitutional symptoms may set in and run much the same course as internal anthrax. But at first the disease is a purely local one, and energetic treatment by excision or cauterisation of the affected tissues will prevent its becoming general, and save the patient from a probably fatal issue.
Post-mortem appearances vary much in detail in different animals. Generally speaking, the blood is dark and uncoagulated; most of the internal organs, particularly the spleen, are swollen and congested; jelly-like infiltrations, either yellow or in large measure composed of blood, are found in various situations, particularly where there is much loose connective tissue—e.g. beneath the peritoneum; there are hemorrhages into the tissues; and often fluid effusions in the serous cavities. On microscopic examination, the capillaries in affected parts are found distended with blood containing abundant bacilli; and the kidneys, spleen, &c. are inflamed.
Bacillus Anthracis.—The characteristic organism, the bacillus, which is the cause of this disease, consists of straight or slightly curved rod-shaped bodies, usually about 0.001 millimetre ( in.) in thickness, and from 0.005 to 0.02 millimetre ( to in.) in length. They are composed of a number of joints, rather longer than broad, each of which consists of an envelope with protoplasm in its interior. The rods increase in length by transverse division of these cells, never become branched, and are motionless. When they are exposed to the air (not within the animal body), bright glistening oval spores may be seen to develop within some of the cells. The bacilli can grow in any fluid containing nutritive material, and at any temperature between 15° and 45° C. (60° and 113° F.), best between 25° and 40° C. (77° and 104° F.). Provided air has free access to the bacilli, spores may form at any of these temperatures. While the bacilli themselves are readily killed by freezing, boiling, complete drying, or the action of antiseptics, the spores are extremely tenacious of life, and dry wool, blood, &c. containing them probably retain their virulence for years.
Preventive Inoculation (badly named 'animal vaccination').—In 1881 Pasteur announced that by cultivating this bacillus at 42–43° C. (108° F.), he was able to obtain a form which produced a modified anthrax in sheep and cattle inoculated with it, much less virulent and fatal than the ordinary disease; and that the animals thus treated were proof against the ordinary anthrax poison. The previous year Toussaint obtained similar results by a slightly different process. Subsequent experimenters have not fully confirmed Pasteur's results; but his method is largely employed on the Continent, frequently, though not always, with success. He stated in 1886 that half a million animals are inoculated annually for anthrax in France alone. Klein has found that the blood of white mice killed by anthrax produces a mild protective attack in sheep. Roy obtained similar results in the case of cattle and horses (but not sheep), with blood from the biscacha or prairie-dog, when investigating the disease in the Argentine Republic in 1883. Among other difficulties in the use of accurate results is the very different susceptibility to the disease even of different breeds of the same species of animal; e.g. one breed of sheep may be killed by a virus which produces a mild protective attack in another. At best, moreover, the immunity conferred by inoculation seems not to last more than a year.
These facts, and somewhat similar results obtained by inoculations in the case of other infectious diseases of animals (black-leg, chicken cholera, pleuro-pneumonia, or foot-and-mouth disease), have special interest from the analogies they present to smallpox and its prevention by vaccination, and seem to point to indefinite possibilities in regard to methods of dealing with other similar maladies. See Reports of Medical Officer to Local Government Board for 1880-81-82-83; Koch On Traumatic Infective Diseases (1880); Klein in The Practitioner for 1884.