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anthrax (ănˈthrăks), acute infectious disease of animals that can be secondarily transmitted to humans. It is caused by a bacterium (Bacillus anthracis) that primarily affects sheep, horses, hogs, cattle, and goats and is almost always fatal in animals. The bacillus produces toxins that kill cells and cause fluid to accumulate in the body's tissues.
Anthrax spores, which can survive for decades, are found in the soil, and animals typically contract the disease while grazing. Transmission to humans normally occurs through contact with infected animals but can also occur through eating meat from an infected animal or breathing air laden with the spores of the bacilli. The disease is almost entirely occupational, i.e., restricted to individuals who handle hides of animals (e.g., farmers, butchers, and veterinarians) or sort wool.
In the cutaneous, or skin, form of the disease, which is not usually fatal to humans, the bacillus enters the skin through a scratch, cut, or sore. Pustules occur on the hands, face, and neck; if the disease is not treated with antibiotics, the bacteria can migrate to the blood vessels, causing septicemia (blood poisoning) and death. Gastrointestinal anthrax is more likely to be fatal. Nausea, vomiting, and fever can be followed by abdominal bleeding, tissue death, and septicemia. Pulmonary, or inhalation, anthrax begins with flulike symptoms and ultimately causes lesions in the lungs and brain. It is rarer, but is usually fatal if not treated early. Because of this, individuals without symptoms who have been exposed to inhaled anthrax are treated with antibiotics for 60 days, anthrax vaccine, and other measures.
Anthrax is a well-known, ancient disease; the fifth plague visited upon the Egyptians in Genesis (see plagues of Egypt) resembles the disease. Pure cultures of the anthrax bacillus were obtained in 1876 by Robert Koch, who demonstrated the relationship of the microbe to the disease. Confirmation of the bacillus as the cause of anthrax was provided by Louis Pasteur, who also developed a method of vaccinating sheep and cattle against the disease. Anthrax is now uncommon in the United States because of widespread vaccination of animals and disinfection of animal products such as hides and wool.
Anthrax spores have been used experimentally by various nations as a biological warfare agent, but effective delivery of anthrax to a population is difficult, and such use is now banned by international convention. Because anthrax has been tested as a biological weapon, the United States has developed a vaccine for military use, but it requires several injections and annual boosters. An accidental release of anthrax from a military laboratory near Sverdlovsk (now Yekaterinburg) in the Soviet Union resulted in 68 deaths from pulmonary anthrax in 1979. In 2001 a number of people in the United States were exposed to spores that were sent through the mails and contracted anthrax; several persons died. Although these bioterror attacks occurred shortly after the terrorist attacks on the World Trade Center and the Pentagon, it did not appear to be linked to them.
S. D. Jones, Death in a Small Package (2010).
An acute infectious zoonotic disease caused by the bacterium Bacillus anthracis and primarily associated with herbivorous mammals. Carnivorous mammals, birds, reptiles, amphibians, fish, and insects are generally resistant to anthrax infection. However, carnivorous and omnivorous mammals often succumb after ingestion of infected meat containing the anthrax toxins, which can cause swelling in the throat and suffocation. Humans primarily present with cutaneous lesions, appearing as black scabs or eschars, after contact with infected animals, carcasses, or animal products. See Zoonoses
Anthrax is responsible for the deaths of thousands of domesticated and wild herbivorous animals annually. Parts of Africa, Asia, southern Europe, and North and South America are subject to repeated outbreaks. In the Western Hemisphere, anthrax is well controlled in livestock.
Bacillus anthracis is a gram-positive, rod-shaped, endospore-forming bacterium, approximately 1.0–1.2 micrometers in diameter and 3–8 μm long. The spores resist drying, cold, heat, and disinfectants, and can remain viable for many years in soil, water, and animal hides and products. Bacillus anthracis possesses three virulence factors: lethal toxin, edema toxin, and a poly- d -glutamic acid capsule. Lethal toxin is composed of two proteins, lethal factor and protective antigen. The protective antigen is produced by the anthrax bacillus at a molecular weight of 83 kDa, but must be cleaved by either serum or target cell surface proteases to 63 kDa before it complexes with lethal factor to form lethal toxin. The edema toxin is composed of edema factor and protective antigen, and it is believed to complex in a manner similar to that seen for lethal toxin. Protective antigen plays a central role in that it is required for transport of lethal factor and edema factor into host target cells. The macrophage appears to be the primary host target cell for lethal toxin, whereas the neutrophil appears to be the target cell for edema toxin in addition to other cells involved in edema formation. The third virulence factor is the capsule, which inhibits phagocytosis through its negatively charged poly- d -glutamic acid composition. All three toxin components are encoded by a plasmid, pXO1, whereas the enzymes required for capsule synthesis are encoded for by the pXO2 plasmid. Strains lacking either or both plasmids are avirulent, such as the veterinary vaccine Sterne strain, which lacks the pXO2 plasmid.
Anthrax consists of two clinical forms, cutaneous and septicemic. The cutaneous form begins as a blisterlike lesion that eventually becomes an intensely dark, relatively painless, edematous lesion forming a black eschar. The lesions rapidly become sterile after antibiotic therapy and take several weeks to resolve, even with treatment. The cutaneous form is reported only in humans, rabbits, swine, and horses.
The septicemic form arises from various initial sites of infection, including cutaneous, oropharyngeal, gastrointestinal, or inhalational exposures. The course of septicemic disease depends on the exposure route and the susceptibility of the animal host. The vast majority of systemic anthrax cases in herbivorus animals occur from trauma to mucosal linings of the mouth and upper alimentary canal caused by ingested fibrous foods. Inhalation anthrax is believed to be initiated by phagocytosis of spores within the lungs by alveolar macrophages. Spore-laden macrophages pass through lymphatic channels to the sinuses of regional lymph nodes or migrate to the spleen, where the spores germinate within the macrophages, multiply, and overwhelm and escape the macrophages to invade the efferent lymphatics. For other portals of entry, mesenteric lymph nodes become involved. The bacilli move to the spleen, where they induce pronounced splenomegaly (enlargement of the spleen), and finally enter the bloodstream, where they induce secondary sites of infection, massive bacillemia, toxemia, and sudden death. Failure of the blood to clot, hemorrhages of skin, hemorrhagic meningitis, and reduced rigor mortis are frequently found in anthrax-infected carcasses. Exposure of contaminated body fluids to the lower atmospheric levels of carbon dioxide results in sporulation of the bacilli. Therefore, opening of infected carcasses should be avoided.
Besides its central role for binding the lethal and edema toxins to target cells, protective antigen plays an important role in the host's protective immune response against anthrax, hence the term protective antigen. Vaccines lacking protective antigen are not protective. For United States and United Kingdom human anthrax vaccines, protective antigen bound to aluminum salts is the principal immunogen. However, veterinary vaccines are composed of viable spores of B. anthracis Sterne strain, a nonencapsulated toxigenic variant. Full protection against anthrax with the veterinary vaccine is afforded by primary and annual booster vaccinations. See Infectious disease
an acute infectious disease of animals and man that is caused by Bacillus anthracis. The causative agent forms spores that can survive in the soil for years and withstand boiling for as long as one hour.
In man. The main sources of anthrax are diseased animals. Infection may result from caring for a diseased animal, slaughtering and dressing a diseased carcass, or eating infected animal products, for example, infected meat and milk. The disease is also transmitted by contact with an infected animal, for example, with its wool, skin, or bristles, or by contact with contaminated soil and water.
Anthrax is often an occupational disease, for example, of livestock breeders. Forms of the disease include cutaneous, intestinal, and pulmonary anthrax; the last two occur more rarely. Infection with cutaneous anthrax occurs through superficial wounds of the skin or as a result of bites from such insects as tabanids and stable flies. The incubation period ranges from a few hours to eight days. The area where the causative agent enters the skin is characterized by the development of edema and a red spot that successively changes into a nodule, blister, pustule, and black scab. The scab is frequently surrounded by small blisters that coalesce in two or three days into one painless ulcer. Other symptoms include high temperature, headache, and weakness.
Intestinal anthrax is characterized by nausea, bloody vomiting, bloody diarrhea, and pain in the abdomen and lower back. The symptoms of pulmonary anthrax include chest pains and a cough initially containing mucous sputum and later blood. Intestinal and pulmonary anthrax, which result in death in two to four days, are rarely encountered in the USSR. The septic fulminant form of the disease, in which the causative agent penetrates the blood and causes a systemic infection, is also rare.
A stable immunity to anthrax results from having the disease. The bacteriological method and an intracutaneous test with anthraxin are used to make a diagnosis. Treatment includes the use of anthracic gamma globulin and antibiotics. The implementation of health and veterinary measures and the establishment of a quarantine are preventive actions that can be taken; the health education of the population should also be provided. Individuals in danger of being infected are immunized with a live vaccine. Persons who have been in contact with infected persons, animals, or animal products are administered anthrax gamma globulin and antibiotics. Those who have contracted anthrax must be hospitalized in order that the focus of the disease may be disinfected.
V. L. VASILEVSKII
In animals. Anthrax is characterized by septicemia and the serous and hemorrhagic infiltration of subcutaneous and subserous connective tissue. There were outbreaks of the disease even in ancient times. It was frequently epizootic, killing enormous numbers of livestock. More than 660,000 animals (excluding reindeer) contracted anthrax in Russia from 1901 to 1914, and 84 percent of this number died. Anthrax is distributed worldwide and is especially widespread in East Africa and West Asia. Cases of the disease were reported in 99 countries in 1972. Only sporadic cases and outbreaks occur in the USSR.
Sheep, goats, cattle, buffalo, horses, asses, deer, and camels are particularly susceptible to anthrax, whereas swine are rarely susceptible. Wild ungulates and rodents may also contract the disease. Carnivorous animals often become infected with anthrax after eating infected carcasses; their feces may for a long period of time contain spores of the causative agent.
Thus, sick animals are a source of the disease’s causative agent. An infected carcass is a great danger to the environment, especially to the soil. The spores of the causative agent are highly resistant to the environmental conditions, and, as a result, contaminated soil is dangerous for herbivorous animals for dozens of years. Plowing and excavating in areas where animal carcasses are buried bring spores to the surface from deep in the soil; the overflowing of rivers can have the same result. Infection is primarily through feed and water and generally occurs in pasture. The causative agent may also penetrate injured skin, oral mucosa, and conjunctiva. Animals are often infected by stinging insects in wooded areas.
There are two forms of the disease: cutaneous, or carbuncular, anthrax and intestinal anthrax. Cutaneous anthrax generally occurs in horses and cattle and is characterized by the appearance of burning, solid, and painful edemas at the site of entry of the causative agent or, secondarily, on the head, chest, shoulders, udder, and mucosae. Ulcers with uneven edges subsequently develop at the site of the edemas. The intestinal form is characterized by functional disturbances of the gastrointestinal tract, including bloat in cows, colic in horses, and the excretion of bloody masses from the rectum in some animals.
The disease may occur in fulminant, acute, subacute, or chronic form. In the fulminant form the animal dies in a few hours after experiencing convulsions and difficult breathing. Bodily discharges include a bloody foam from the nose and mouth and dark blood from the rectum. In the acute form the body temperature rises, and the mucosae become cyanotic. The animals are either extremely depressed or excited; the gastrointestinal tract becomes disturbed and pregnant animals abort. Blood oozes out of body openings after death. Subacute and chronic anthrax are usually observed in swine; tonsillitis or pharyngitis develops, as do lesions of the submaxillary or mesenteric lymph nodes.
Animals that recover from anthrax develop a prolonged and stable immunity. Diagnosis is based on clinical and epizootiological findings and is conclusively confirmed by laboratory tests of pathological material. It is strictly forbidden to open the carcass of a dead animal if anthrax is suspected. The most effective form of treatment is the injection of hyperimmune antianthrax serum.
Preventive and control measures include the implementation of sanitary measures to improve conditions in endemic areas. If anthrax occurs the farm involved is quarantined, sick animals are isolated and treated, farm buildings are disinfected, and carcasses are burned. If diseased animals die in a field, the soil is disinfected and replowed. The other farm animals are immunized.
REFERENCESibirskaia iazva. Moscow, 1970.
a genus of flies of the family Bombyliidae. The body length is approximately 1 cm. The wings are dark, with light spots near the tip. The body is black, with white markings. Adults are usually predators but are also found on flowers. The larvae parasitize the caterpillars and pupae of butterflies and the egg packets of locusts, as well as the parasites of these insects. The genus is distributed mainly in the steppe and desert zones. In the forest zone they are found in open places. They are active in sunny weather.