Anthrax

C. D. STEIN AND G. B. VAN NESS.

ANTHRAX, or splenic fever, is an acute, infectious, febrile disease that has a rapidly fatal course. Sometimes it is referred to as charbon and milzbrand in animals, and as a malignant pustule and the woolsorter's disease in people.

Anthrax is one of the oldest and most destructive diseases of livestock. Outbreaks that took many animal and human lives are recorded by many medieval and modern writers. The disease has been associated closely with early discoveries that lead to the development of the modern sciences of bacteriology and immunology. It was the first infectious disease of animals in which the causative agent was definitely demonstrated to be a specific micro-organism and the first disease against which a bacterial vaccine was found to be an effective and practical means of prophylaxis.

The specific cause of anthrax is Bacillus anthraces, a Gram-positive, non-motile, spore-forming, rectangular-shaped bacterium of relatively large size. The growing bacilli are usually arranged in chain formation in animal tissue or cultures, but they may occur singly or in pairs. When properly stained, the bacilli in blood and tissue smears of animals dead of the disease usually reveal a distinct capsule.

The organisms are highly virulent. When they gain access to the animal body, they multiply rapidly, invade the blood stream, and produce a rapidly fatal blood infection (septicemia). It, the presence of oxygen, sufficient moisture, and a favorable temperature, the bacilli develop spores of remarkable tenacity. It is generally believed that spores do not form in the unopened carcass, but sporulation occurs readily when organisms are discharged from the body of an infected animal or when the carcass is opened for autopsy.

Anthrax spores are highly resistant to heat, low temperatures, chemical disinfectants, and prolonged drying.

They may retain their viability for many years in the soil, in water, on hides, and on any contaminated objects held in storage.

On some marshy or bottom land or in soils that contain decomposed vegetable or animal matter, the organisms survive for long periods. In anthrax districts where the soil is known to be seriously infected, the disease may occur in epizootic form among livestock on pasture, especially during late summer and early fall, when grazing is closer because of scanty pasturage and when flies are numerous. Anthrax tends to be seasonal, but sporadic outbreaks may occur anywhere at any time.

ANTHRAX OCCURS in all parts of the world. Districts where repeated anthrax outbreaks occur exist in southern Europe, parts of Africa, Australia, Asia, and North and South America.

Large recognized areas of infection exist in South Dakota, Nebraska, Arkansas, Mississippi, Louisiana, Texas, and California, and small areas exist in a number of other States. Anthrax has been recognized as a disease of livestock in the United States for more than 60 years. There were 3,447 outbreaks in 39 States, with losses of 17,604 head of livestock, between 1945 and 1955.

Anthrax is spread from one country to another mainly through infected animals and the interchange of infected objects closely associated with animal life, such as hides, hair, wool, bonemeal, meat scraps, fertilizer, and forage.

When anthrax is once established in an area, it may spread to adjoining localities and even to distant points by contamination of soil, drinking water, and pasture plants with discharges of diseased animals; by dogs, cats, coyotes, and other carnivore that have fed on infected carcasses; by carrion-eating birds, especially buzzards; by flies and possibly other types of insects; by streams contaminated with surface drainage from anthrax-infected soil and tannery wastes; and by mixed feeds containing contaminated bone-meal, meat scraps, and other animal proteins.

All animals are susceptible to anthrax in some degree. Cattle, horses, sheep, and goats are most commonly affected. Man and swine possess a greater natural resistance to the disease. Dogs, cats, and wild animals of prey, as well as birds, frogs, and toads may become infected under certain conditions. Mice, guinea pigs, and rabbits, which are commonly used in the laboratory diagnosis of anthrax, are highly susceptible, but rats have considerable resistance.

Infection in cattle, horses, mules, sheep, and goats is usually the result of grazing on infected pastureland. Infection may also be caused by contaminated fodder or artificial feed-stuffs, such as bonemeal, blood meal, oilcake, and tankage; by drinking from contaminated pools; or by the bites of contaminated flies. Swine, dogs, cats, mink, and wild animals held in captivity usually acquire the infection from consumption of infected meat. Widespread outbreaks in herds of swine in the Midwest in 1952 were traced to mixed feeds containing contaminated bonemeal.

THF, SYMPTOMS OF ANTHRAX vary according to the species of animals and the acuteness of the attack. The average period of incubation that is, the period of time elapsing between exposure to infection and the appearance of the first symptoms under natural conditions is not known definitely, but experimental evidence indicates it may vary from 24 hours to 5 days or much longer.

The disease may occur in a peracute, acute, subacute, or chronic form.

The peracute form, most common in cattle, sheep, and goats, occurs at the beginning of an outbreak and is characterized by its sudden onset and rapidly fatal course. Victims present a picture of cerebral apoplexy sudden staggering, difficult breathing, trembling, collapse, a few convulsive movements, and death. Death may occur without any noticeable illness.

In the acute and subacute forms, most common in cattle, horses, and sheep, there is first a rise in body temperature and a period of excitement, followed by depression, stupor, spasm, respiratory or cardiac distress, staggering convulsion, and death. During the course of the disease, the body temperature may reach 107 F. Rumination ceases, the milk secretion of milking cows is materially reduced, and pregnant animals may abort. Bloody discharges may emanate from the natural body openings. Swellings may appear in different parts of the body.

Horses may show fever, chills, severe colic, loss of appetite, extreme depression, muscular weakness, a bloody diarrhea, and swellings in the region of the neck, sternum, lower abdomen, and external genitals. The acute form usually terminates in death in a day or two. The subacute form may result in death in 3 to 5 days or longer or recovery.

A cutaneous, or localized, form of anthrax characterized by swellings in various parts of the body may occur in cattle and horses when anthrax organisms lodge in wounds or abrasions of the skin. This form of the disease may occur following bites by infected flies or in highly susceptible animals following vaccination.

Chronic anthrax, with local lesions confined to the tongue and throat, occurs mostly in swine but is observed occasionally in cattle, horses, and dogs.

The symptoms of anthrax in swine are marked swellings of throat and tongue. Often a blood-stained, frothy discharge comes from the mouth.

Some swine may die of acute anthrax without having shown any previous signs of illness. Others in a herd may have a high temperature, loss of appetite, depression, and rapidly progressing swelling about the throat, which sometimes causes death by suffocation. A comparatively large percentage may develop the disease in a mild and chronic form and may make a gradual recovery; some of them, when presented for slaughter as normal animals, however, on the postmortem examination may show some evidence of chronic anthrax infection in the cervical lymph glands and tonsils.

In animals dead of anthrax there is usually an oozing of blood from the nostrils and anus, rapid decomposition, and marked bloating. The blood fails to clot readily and is darker than normal. Rigor mortis (stiffening of the muscles) is frequently absent or incomplete. Hemorrhages beneath the skin are common. Clear or blood-tinged gelatinous exudates are found at the site of swellings. The spleen is usually greatly enlarged. The splenic pulp is soft or semifluid in consistency and dark red to black. The liver, kidneys, and lymph glands are usually congested and enlarged.