Organism Bacillus anthracis is a rod-shaped organism occurring in pairs or chains and staining positively with Gram's stain. In the vegetative state in the animal or where there is a low oxygen content, the bacillus is surrounded by a capsule. If the dead animal's tissues become exposed to the air or the organism is cultured aerobically, then spores develop, which appear as round-filling defects in the stained rods.

The vegetative form is killed by heat at 55°C for 1 h, or if the carcass is not opened, putrefaction will raise the internal temperature sufficiently (30°C for 80 h) to render it free of organisms. However, if it is butchered or a post-mortem performed, then exposure to the air encourages the development of highly resistant spores, which are one of the most persistent forms of life known. They have survived 160°C for 1h and -78°C despite thawing and re-freezing, while in pastures they have been found viable after 12 years and possibly up to 60 years.

Clinical features Essentially an infection of cattle, anthrax ranks with rabies and plague as a much feared and fatal disease. Infection commences with a small papule at the site of inoculation. By the second day, a ring of vesicles surrounds the lesion, which are at first clear, but then become blood-stained. The central papule then ulcerates and enlarges to form a depressed dark eschar, which increases in size and darkens to the black coal colour that gives the disease its name (anthrax is coal in Greek). Pus is never present despite the development of oedema around the lesion. The oedema is extensive and may cause respiratory embarrassment if around the neck. The associated lymph nodes are often enlarged, but must be left to resolve spontaneously. The primary lesion commonly occurs on the head or face, while the neck and forearm are also often affected. Surprisingly, the fingers are rarely involved.

As well as the primary lesion and its surrounding oedema, there are systemic symptoms of varying severity. The patient feels unwell although the temperature is normal or only slightly raised. A high temperature or weak pulse is a serious sign, generally indicating pulmonary disease, which results from the inhalation of a large dose of spores. Illness sets in rapidly with cough, dyspnoea and cyanosis. Lymph nodes enlarge and there is splenomegaly. This passes into a stage of cardiovascular collapse and the patient is dead within 2-3 days.

Intestinal anthrax is another uncommon, but severe form of the disease resulting from people eating infected meat. The primary lesion occurs in the intestines and the massive oedema that results produces intestinal obstruction as well as systemic symptoms. However, cutaneous anthrax is the commonest form even in people who butcher and subsequently eat an animal that has died from anthrax.

Diagnosis is made by examination of the fluid from the vesicle in a person who gives a history of contact with an animal that recently died. A smear is made on to two slides, one being stained by Gram and the other fixed by heat and stained with methylene blue or Giemsa. The first shows Grampositive rods and the second demonstrates the red capsule surrounding the blue bacilli. This finding can be confirmed by culture on selective media.

Transmission Anthrax spores are ingested or become accidentally inoculated through the skin, such as by thistle scratches around the muzzle or legs of an animal close grazing in an infected pasture. Biting flies have also been incriminated. The spores germinate into the vegetative form, which rapidly invades, increasing in virulence. A local lesion grows at the point of inoculation and extensive oedema develops around it. The capsulated bacilli produces a lethal factor, which causes anoxic hypertension or cardiac collapse, resulting in sudden death of the animal. After death, the animal appears black from tarry blood that is slow to clot.

People are infected by contact with the deceased animal, either in butchering and handling of the infected meat, or at a place far removed from the death of the animal from spores in its hide, hair or bones.

Incubation period is less than 7 days, with as short as only 2 days in the rapidly fatal pulmonary form.

Period of communicability Not transmitted from person to person.

Occurrence and distribution The disease commonly affects cattle, sheep, goats and horses, but has occurred in dogs and cats. It is probably widespread in the wild and has been found in elephants, hippopotamuses and on the claws and beaks of vultures and other scavenger birds. Widespread in the bovine populations of the world, its persistence in the environment and in the produce of cattle makes it an ever-present threat both in the developing and developed world. It is a particular problem in Africa, Southwest Asia, Russia, South and Central America.

Control and prevention is difficult due to the persistence of the organism in the environment, but once an outbreak starts, it should be possible to bring it to an end by vigorous control of animals and their slaughter. No animal that dies from anthrax should be allowed to be butchered and sold for meat. Its hide and bones are also infectious, so should be deep buried with lime or burnt. Anthrax is a common disease in pasturalists. For fuel, they often conserve dried cow dung, which also makes an ideal material to incinerate the carcass as it burns slowly but continuously.

The animal should not be cut open to obtain specimens or perform autopsy, but cutting off an ear is quite sufficient for diagnostic purposes.

Once anthrax is recognized, then all animals should be vaccinated with a live, attenuated vaccine. Due to the persistence of the organism in the soil, especially at a site where an infected animal has been buried, anthrax is likely to recur year after year at the same site, so-called anthrax districts. Hot, moist areas are particularly liable to offer the right conditions for continuous sporulation and germination, leading to a steady infectious state throughout the year. In contrast, hot arid areas encourage spore formation and when the vegetation dries out, close grazing brings the animal into proximity with the spores in the dust, so a dry season outbreak is more common. This can be anticipated and cattle vaccinated prior to the anthrax season.

Anthrax is an occupational disease in those persons who deal with hides, hair (including wool) and bones of animals. The spores can persist almost indefinitely in these animal remains and when tested are found to be present in a large proportion. Pasturalists particularly will not waste an animal that dies and taking off its skin and leaving the bones to dry in the sun encourages formation of spores which remain with these products when they are shipped all over the world. It is an impossible task to identify these infected animal products and because of the high proportion involved, an uneconomical process to destroy them. Quite surprisingly, people who handle infected hides and products only rarely develop anthrax, but they should, of course, be warned and provided with facilities to be examined and treated. Protective clothing should be provided and a ventilation system to remove spores from the air when unpacking, beating or a similar process occurs. Many industrial processes disinfect the animal products, but where this does not occur, sterilization can be introduced. With persons at increased risk of developing anthrax, vaccination can be offered. The vaccine is from a sterile filtrate of B. anthracis and is given in 0.5 ml doses at 6 weeks after the initial dose, then 6 months and thereafter at annual intervals. Modified anthrax can occur in the vaccinated.

Treatment is with penicillin to which the organism is very sensitive. Benzylpenicillin 4 million IU every 4-6 h for 7 days or if still available, procaine penicillin 1 mega unit daily for 3 days can be used. No local treatment is required and surgical removal of the eschar or incision of oedema only leads to unpleasant scarring and development of intractable sinuses. Ciprofloxacin or doxycy-cline can be used for respiratory and intestinal cases. Supportive measures need to be given for shock and tracheostomy may be required when there is severe oedema of the neck.

Surveillance Anthrax is a notifiable disease in many countries. Where no animal source can be shown, then bioterrorism should be considered (Section 18.5).

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