Synonyms: sometimes referred to as splenic fever (but this term can be used for other diseases too) and formerly known as woolsorter’s disease.

What is it?

Anthrax is a non-contagious zoonotic bacterial disease caused by the spore-forming bacterium, Bacillus anthracis. B. anthracis is transmitted by the spores it forms when exposed to air. These spores can survive for decades in the environment but only develop and multiply as bacteria when a susceptible individual absorbs them. Herbivorous mammals are particularly susceptible but omnivores, including human, and carnivores may also be infected and even die from the disease. There are three ways in which infection occurs: when spores are swallowed, through inhalation or when spores come into contact with the skin. Animals are mostly infected through the digestive route, whereas all three routes are reported in humans. The cutaneous form of the disease is relatively common among butchers and tanners handling infected meat and hides. The aerial route used to be common among woolsorters. Infection through the digestive route occurs when contaminated food or infected animals are consumed. Herbivores usually become infected when grazing on short grass (close to the ground where the spores persist). Infection through the licking of bones of animals that died of anthrax was also reported in herbivores in search of minerals.

The pulmonary and gastro-intestinal forms are the most severe and often lethal. The death of the host contributes to the dissemination of B. anthracis: B. anthracis produces numerous spores when fluids and tissues of infected animals are exposed to air, for instance when fluids drain out of carcasses or when dead animals are cut open. Spores can survive in contaminated soil for decades. Chalky and alkaline soils increase their survival. Sandy soils and floods have a tendency to bring the spores to the surface of the earth.

As opposed to the spores, the unsporulated bacteria die within a few days during the decomposition of unopened carcasses.

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How to recognize it

In herbivores, anthrax is usually an acute disease causing the death of animals without specific symptoms. Staggering, trembling and dyspnea (breathlessness) may be seen in some animals, followed by rapid collapse, terminal convulsions and death. In less acute forms, fever and excitement followed by depression, stupor, disorientation, muscle tremors, dyspnea and congested mucous membranes may be observed 1 or 2 days before death. Pregnant cows may abort, and milk production can drop dramatically. Bloody discharges from the nose, mouth and anus are sometimes seen. In dead animals, rigor mortis is usually absent or incomplete, and the carcass is typically bloated and decomposes rapidly. Post-mortem examinations should be carried out with extreme caution if anthrax is suspected because of the risk of sporulation and contamination of the soil. Signs of blood infection are obvious: the blood is dark, thick, does not clot readily and petechiae (small reddish spots indicative of bleeding under the skin) are abundant. Hemorrhages and ulcers are also common in the intestinal mucosa and the spleen, which is usually enlarged, has a ‘blackberry jam’ consistency.

Diagnosis is based on the identification and isolation of bacteria from blood or biopsies. Serology and skin tests are sometimes useful for the retrospective diagnosis of an outbreak.

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In humans, three forms are described.  With the exception of bioterrorist attacks, the pulmonary form, which is the most lethal, has become very rare since countries involved in the wool industry have controlled the disease. The cutaneous form is often an occupational disease of people working with animal products, skins and hides. Cutaneous anthrax is characterized by a papular (pimple like) skin lesion, which becomes surrounded by a ring of fluid-filled vesicles. The central papule ulcerates, dries and develops a firmly adherent, depressed black scab. The skin lesion is usually painless, but it is often surrounded by significant edema (fluid retention). Fever, pus and pain are seen only if secondary infections occur. Cutaneous lesions often heal spontaneously but fatal infections occur in approximately 20% of cases. Small anthrax lesions usually heal with minimal scarring, inducing immunity. Gastrointestinal anthrax develops after eating contaminated meat. When spores germinate in the intestinal tract, they cause ulcerative lesions. Reported cases range from asymptomatic infections to fatal disease. Symptoms include malaise, fever, nausea, vomiting, diarrhea and anorexia (lack of appetite). Severe gastrointestinal symptoms may be observed: severe abdominal pain, blood in stools (faeces) and bloody diarrhea. Severe gastrointestinal anthrax rapidly progresses to shock, coma and death. This form of anthrax may not always be severe and some people may recover spontaneously.

Diagnosis is based on the identification and isolation of bacteria from biopsies. Serology and skin tests may be used for retrospective diagnosis.

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Anthrax CDC (English only)

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Disease Fact Sheets Iowa University (p2, English only)

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How to control it

Contaminated soils are the main source of infection for herbivores. Soils remain contaminated for extensive periods of time (several decades), depending on the nature of the soil. Sandy soils and floods tend to bring buried spores up to the surface of the earth. As a consequence, domestic animals grazing in contaminated areas should be vaccinated. More importantly, new contaminations should be avoided by disposing of carcasses in an appropriate way. The principle is that B. anthracis bacteria present in infected animals should not be exposed to air to prevent sporulation: they should not be butchered and post-mortem examinations should not be performed. Soil and objects contaminated by body fluids should be disinfected.

Carcasses should be burned or buried deep and covered with lime. Alternatively, unopened carcasses should be wrapped in sealed plastic sheets and left in the sun to destroy the unsporulated bacteria. People should not eat meat from wild and domestic animals that die of unknown reasons.

A live attenuated vaccine is available for animals. Annual vaccination (1 month before the season when outbreaks generally occur) should be recommended in endemic areas. Human vaccination is restricted to persons at risk (bioterrorism).

Effective treatment in humans depends on early recognition of the symptoms: treatment for cutaneous anthrax is usually effective, but the pulmonary and gastrointestinal forms are difficult to recognize early and the mortality rates are higher. Most natural strains of B. anthracis are susceptible to several antibiotics, including penicillin. (Strains used in bioterrorism are usually resistant to penicillin.)

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Cultural and geographical specificities

Pastoralist communities

People should be advised not to consume meat from animals that died naturally. For the same reason, the slaughter of animals on the point of death and subsequent consumption of their meat also poses danger. Vaccination of animals could be used to reduce the incidence in animals and, consequently, in humans in endemic areas. Pastoralists are usually receptive to livestock vaccination, especially if it protects their animals against a lethal disease.

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Communities in northern Africa and the Sahel region

In many communities religious or traditional dietary rules prohibit the consumption of meat from unhealthy animals or animals that do not bleed. This significantly reduces the risk of human gastro-intestinal infections. Cutaneous cases might exist among butchers and tanners, especially in areas where animal cases are regularly observed. Vaccination of animals could be used to reduce the incidence in animals and, consequently, human cutaneous anthrax. 

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Mixed farming communities in more humid regions

People should be advised not to consume meat from animals that died naturally or from sick animals, including wildlife. Some areas might present high risks of exposure to anthrax. The Zambezi valley, for instance, is known to be endemic because of the composition of the soil and annual flooding. Land that is shared by wildlife and livestock also present serious risks since wildlife that died from anthrax might disseminate spores very widely via the vultures that feed on their carcasses. Vaccination of livestock should be used to reduce the incidence in animals and, consequently, in humans in endemic areas.

An increase in anthrax outbreaks may be associated with interruptions in regular anthrax vaccination campaigns or with political upheavals and food shortages.

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