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overview of the epidemiological cycles of Bacillus anthracis

This figure gives a nice overview of the epidemiological cycles of Bacillus anthracis (

Anthrax infection in humans

Human anthrax infections are often contracted during work activities in oneofthe following fields:

  • Tanneries

  • Wool sorters

  • Bone processors

  • Slaughterhouses

  • Laboratory workers

Infection routes for humans of Bacillus anthrax

When humans become infected, the disease is usually presented as skin wounds that heal very slowly. The bacteria can penetrate the skin if they come in contact with a fresh skin wound.

Cutaneous anthrax ulcus in a human.
anthrax ulcus on the finger of a tannery worker

These photos demonstrate the type of wound that results from such an infection. The person with the wound on the left image worked on a cattle carcass that died from anthrax. While handling this carcass, he injured himself by a sharp bone fragment that was infected with the anthrax bacteria ( The person on the right image is probably a tannery worker, who infected himself by rubbing his knuckles on the skin of an animal that died of anthrax (

Severe wound caused by Bacillus anthracis on the arm of a humen that needs immediate treatment

If untreated or if the infected wound is big, the bacteria can spread in a large area around the wound, as is shown here. This severe wound needs immediate treatment with the right antibiotic.

Anthrax spores can also be inhaled. In the lungs the anthrax bacteria can cause a very severe inflammation. On the left image you can see an X-ray of healthy lungs, with a clear heart shadow. On the right X-ray you can distinguish a big mass in the thorax that does not allow the x-rays to get through. If this disease is left untreated until obvious symptoms occur, it is usually fatal. This patient had a business where he made drums using cattle and goat skins imported from Africa. He died 1 day after this X-ray was made. (

Radiograph of healthy human lungs
Radiograph of the chest of a person with sever pneumonia caused by Bacillus anthracis

Anthrax infection in animals


Typically, the incubation period is 3–7 days (range 1−14 days). The clinical course ranges from peracute to chronic. The peracute form (common in cattle and sheep) is characterized by sudden onset and a rapidly fatal course. Staggering, dyspnea, trembling, collapse, a few convulsive movements, and death may occur in cattle, sheep, or goats with only a brief evidence of illness. Often, the course of disease is so rapid that illness is not observed and animals are found dead. A very characteristic feature of acute anthrax is free non-coagulating blood running from body openings, due to the disturbed coagulation.


The disease in horses may be acute. Signs may include fever, chills, severe colic, anorexia, depression, weakness, bloody diarrhea, and swellings of the neck, sternum, lower abdomen, and external genitalia. Death usually occurs within 2–3 days of onset.


Anthrax bacteria disturb the natural blood coagulation. This results in bleedings in the skin and all internal organs. Non-coagulated blood is collected in the lymph nodes, while free-running blood appears from all openings. These symptoms usually lead to a sudden death.

Lion that died of anthrax. Note the free running blood from the nose
Kudu that died of anthrax. Note the multiple small bleedings in the skin

Anthrax can affect multiple species, like cattle and wild ruminants (greater kudu), zebras as well as predators (lion). Note the running blood from nostrils or eyes in all these animals and the small bleedings in the skin of the kudu.


Hippopothamus that died of anthrax
Kudu that died of anthrax. Note the multiple small bleedings in the skin
Zebra that died of anthrax. Note the free running blood from the nostrils

Multiple outbreaks of anthrax in wild hippopothamus has been reported in several southern African countries (

Cow that died of anthrax. Note the free running blood from the eyes and the nose
Schematic drawing of Bacillus anthrax. Note the spores and the sharp edges of the bacteria.
Bacillus cereus. Note the long chain of bacteria with rounded edges, which differentiate them from B.anthracis

Animal to animal transmission


There are several ways of transmission of B. anthracis between animals. Animals grazing in areas where anthrax victims have been buried, can be infected when the carcass remnants are digged up either by the feeding animal or through human activities (road or building constructions). Flies that have fed on an anthrax-carcass can easily spread the bacteria through their droppings that remain on leaves. Predators (big cats) that feed on infected carcasses can become infected and die of anthrax.

Flies feeding on an anthrax carcass
Flies feeding on an anthrax carcass. B.anthracis can be found in the droppings of the fly
Droppings of flies that have been feeding on an anthrax carcass
Flies feeding on an anthrax carcass. B.anthracis can be found in the droppings of the fly

Flies that feed on an infected carcass may spread B.anthacis through their droppings as illustrated on these images (

Anthrax in elephants


Anthrax in elephants is usually a gastro-intestinal infection. The animal ingests the spores while feeding food or water contaminated with spores. After an incubation period of a few days, the animal dies of septicemia. Multiple cases have been reported from several range countries in Asia (Kumaraguru A. et al. 2015). In some areas Asian elephants play a role in the transmission of anthrax between wildlife and farm animals (Walsh M.G. et al. 2019). Like in other mammals, symptoms consist of rapid detoriation after infection. Usually the elephant is found dead before symptoms were observed. Running blood from the trunk, mouth, eyes, rectum or vagina should alarm the finder of the carcass for this being an anthrax case.

Anti-PA antibodies were detected in elephants, which suggests that they can mount adaptive immune responses against anthrax. In addition, these results suggest that elephants can be infected with anthrax and survive infection under some circumstances (Cizauskas et al. 2014).

A fatal case of anthrax in a 15-yrs-old African elephant was reported from a wildlife park in Nigeria (Okewole, 1993). Frequent urination, restlessness and weakeness of the hind quarters were observed prior to death. A co-infection with Cowdria ruminatium was diagnosed at post mortem examination (coccoid intracytoplasmatic bodies in the endothelia of the brain).

Asian elephant victim of anthrax. Note the free running blood on the ground in the area of the head

A wild Asian elephant that died of anthrax in the forest of Myanmar. Note the amount of free running blood around the head. Photo courtesy: Myanmar Forest Police

Asian elephant victim of anthrax. Note the free running blood on the ground in the area of the head

A wild Asian elephant that died of anthrax in the forest in India (Kumaraguru A. 2015)


Early detection of the disease is essential, though difficult. Multiple classes of antibiotics can be used if treatment is started in time: oxytetracycline, penicillins, aminoglycosides, fluoroquinolones, macrolides, and sulfonamides. Dosages can be obtained from the website of Elephant Care International:


Diagnosis (post-mortem)

​Post mortem findings in elephants are:

  • Bleedings

    • In and under the skin

    • Around muscles

    • In organs

    • Free blood in the intestines

    • Free blood in the lungs

    • Free blood in the abdomen

  • Edematous swelling of the skin

  • Swollen spleen with bleedings

  • Liver and lymph nodes are swollen and contain a lot of blood


Disposal of an anthrax carcass

If a dead elephant is suspected of anthrax, a full necropsy is not recommended. A blood smear from a small incision made in an ear should first be made and examined microscopically for the presence of Gram-positive stained rods, lying in chains, sometimes accompanied by spores. The carcass should be disposed off as soon as possible in a proper way. The disposal must be done following the next steps:

  • To minimize the spread of blood, you should try to plug the openings (trunk, ears, mouth, anus, vulva) with non-absorbent material. You can also wrap the head of the elephant in plastic and tape it with duct tape or tie it with a rope to the skin of the neck.

  • Don’t move the animal around

  • Incinerate the carcass if possible

  • If incineration is not possible, burry the carcass as deep as possible. Use heavy excavating equipment (backhoe loader) to dig a deep, large hole, at least 2 meters deep

  • Disinfect all materials that have been in contact: 10% formalin or 5% lime solution (sodium hydroxide)


Necropsies of any animal should always be performed with great care. If there are signs of anthrax, a peripheral blood smear should always be examined first. If accidently the diagnose was missed, any signs of internal bleedings should alarm the prosector. B. anthacis can be cultured quite easily. Every necropsy should be performed with adequate body protection: proper eye protection, a respiration mask, long gloves, rubber boots and protective clothing. 


Elephants can be vaccinated against anthrax with commercially available vaccines. This is highly recommended in areas where anthrax is seen in farm animals or if there is a history of anthrax in elephants in that area.

References/further reading



Recommended websites:

General information


Merck Veterinary Manual (2021): Anthrax is a zoonotic disease caused by the sporeforming bacterium Bacillus anthracis. Anthrax is most common in wild and domestic herbivores (eg, cattle, sheep, goats, camels, antelopes) but can also be seen in people exposed to tissue from infected animals, to contaminated animal products, or directly to B anthracis spores under certain conditions. Depending on the route of infection, host factors, and potentially strain-specific factors, anthrax can have several different clinical presentations. In herbivores, anthrax commonly presents as an acute septicemia with a high fatality rate, often accompanied by hemorrhagic lymphadenitis. In dogs, people, horses, and pigs, it is usually less acute although still potentially fatal.

Toxins are the source of most of the disease symptoms associated with anthrax. Edema toxin complex (EdTx) causes the fluid and edema seen in cutaneous anthrax infections, and lethal toxin complex (LeTx) causes shock and death from systemic anthrax (Hanna, 1998).

B anthracis spores can remain viable in soil for many years. During this time, they are a potential source of infection for grazing livestock but generally do not represent a direct risk of infection for people. Grazing animals may become infected when they ingest sufficient quantities of these spores from the soil. In addition to direct transmission, biting flies may mechanically transmit B anthracis spores from one animal to another. The latter follows when there have been rains encouraging a high fly hatch and reporting has been delayed on the index ranch, such that there are 4–6 moribund or dead cattle for the flies to feed on. Feed contaminated with bone or other meal from infected animals can serve as a source of infection for livestock, as can hay muddy with contaminated soil. Raw or poorly cooked contaminated meat is a source of infection for zoo carnivores and omnivores; anthrax resulting from contaminated meat consumption has been reported in pigs, dogs, cats, mink, wild carnivores, and people. Human cases may follow contact with contaminated carcasses or animal products (raw meat, skins of animals that died of anthrax).

Flies that have fed on a carcass from an anthrax victim can spread the disease over longer distances.


Anthrax can be diagnosed in fresh blood smears taken from the ear. Microscopically, B. anthracis can be recognized as long chains of Gram-positive bacteria. If the smear has been exposed to air, the bacteria may have formed spores that can be easily detected. B. anthracis differs in shape from other Bacillus species, that may contaminate the sample in case the animal has been dead for a longer period. Whereas the bacteria chains of B. anthracis seem to be sharply cut off with a knife, the chains of B. cereus have round edges.

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