Explainer | What is Anthrax and why is it dangerous?

Anthrax

Anthrax is an infection that is caused by the gram-positive bacteria called Bacillus Anthracis. Anthrax can either be cutaneous, gastrointestinal or inhalation.

History

Anthrax was known by the names wool sorters and rag-pickers disease in 1800. This was because workers used to contract the disease through bacterial spores present in wool or fabric fibres. Spores are small thick-walled in the dormant stage of some bacteria; this enables them to withstand and thrive under unfavourable conditions. Louis Pasteur perfected the first anthrax vaccine in 1881.

The firth plagues described in some Jewish literature may be among the earliest description of anthrax. Robert   Koch ‘s experiment with anthrax led to the theory of the relationship between bacteria and diseases and John Bell ‘s work in inhalation anthrax led to wool disinfection.

Present

Anthrax at present is common in south pacific Asia, Africa, and the west Pacific region. In the western or instead of first world countries, a significant concern is the use of anthrax in biological warfare. Iraq reportedly produced about 8500L of anthrax. That is why a total of 150,000 United States soldiers were vaccinated after the September 2011 attack of the world trade centre. Most recent cases of anthrax are the use of the postal system to distribute anthrax.

Pathogenesis

The most common form of anthrax is cutaneous and can be contracted by close contact with exposed skin and products taken from infected animals. E.g. cattle, sheep and goats.

Occurrence

Anthrax is caused by gram-positive Bacteria called Bacillus Anthracis, which has a diameter of 1-1.5 micrometres and the width of 3-10 micrometres. Anthrax bacilli tend to form long chains and may appear similar to streptobacilli on culture. Bacillus anthracis produces capsules that can easily be seen through negative staining. The bacteria grows very well in the presence of carbon dioxide and is catalase positive. Anthrax can be differentiated from other gram-positive rods when culturing due to its lack of motility in broth and the absence of hemolysis on blood agar.

Optimal growth conditions result in vegetative phase and bacterial multiplication. Drought or rain can trigger the germination of anthrax spores while flies and vultures are distributors.

Anthrax Bacteria

There are three types of anthrax toxins, the first one is a protective antigen, a lethal antigen and oedema factor. The protective antigen is the 83 KD proteins that bind to cell receptors with the target cell, once bound a fragment is cleaved free to expose another additional binding site. The binding of the oedema factor at this site results in the formation of oedema toxins.

Oedema toxins act by converting ATP to cAMP. The increase in cAMP leads to oedema within the target tissue. It may also inhibit neutrophil phagocytosis; lyse macrophages, because of the release of tumour necrosis factor and interleukin-1. Death occurs is as a result of lethal toxins that are produced, which sometimes causes animals to bleed from all orifices.

Modes of Infection

Cutaneous anthrax

Humans are relatively resistant to cutaneous anthrax. Bacillus Anthracis my gain access through microscopic or gross breaks in the skin. A malignant Pustule (a central area of coagulation, Necrosis surrounded by blisters filled with bloody or clear fluids) Bacillus Anthracis multiply locally and may spread to other organs through the lymphatics. The organism remains in the capillaries and fatality is dependent on the toxins that are produced by the bacteria.

Intestinal Anthrax

Intestinal anthrax mainly affects the caecum and produces a local lesion similar to the one presented in the cutaneous form. In this case, spores invade the Gastrointestinal mucosa, and in some cases, ulceration and necrosis at the site of infection produce GI haemorrhage.

Inhalation Anthrax

Inhalation Anthrax occurs after a person inhales the spores in the lungs. Inhaled spores are ingested by the pulmonary Macrophages and then carried to the hilar and mediastinal lymph nodes. The incubation period is from one to six days. Spores germinate and multiply in the lungs but do not cause pneumonia. Anthrax spores cause haemorrhagic mediastinitis and pulmonary oedema. Pleural effusions frequently accompany inhalation anthrax, and if not treated early the mortality rate is very high.

Clinical Presentation

Cutaneous Anthrax

Cutaneous anthrax begins as papule that enlarges within 24-48 hours to form a 1 cm vesicle, and then it turns into an ulcer surrounded by an oedematous halo. A cutaneous anthrax lesion is usually 2-3 cm in diameter and has a round regular raised edge. If the injury of cutaneous anthrax affects the neck it may cause swelling due to oedema and enlarged cervical lymph nodes may impose stridor and respiratory distress.

Inhalation Anthrax

Inhalation anthrax is usually in two phases. The initial stage begins with Myalgia, Malaise, fatigue and non-productive cough, hypoxaemia and cyanosis. The second phase lasts for 24 hours, the patient may have low fever or hypothermia and develop shock.

According to the CDC, Inhalation anthrax is the most dangerous for, without treatment, only 10-15% of people survive. However, with aggressive treatment, 55% of people with Inhalation anthrax survive.

Intestinal Anthrax

Patients with intestinal anthrax may have severe abdominal pain, multiple ulcerative lesions are found throughout the GI tract secondary to haematogenous spread. Primary intestinal anthrax causes injuries that resemble an ulcer of oropharyngeal anthrax. Intestinal anthrax is hard to diagnose, and death may occur within 2-5 days of onset.

Management

Anthrax is relatively rare in developed countries due to the widespread animal vaccination and practices used to disinfect hides or other animal products. Anyone visiting a country where anthrax is common or was heard animals are not often vaccinated and decontaminated should avoid contact with livestock and eat meat that is poorly prepared. Another form of management is carefully handling dead animals suspected of having anthrax.

In the case of contaminated mail, the precautions include inspecting mail from an unknown for excessive tape powder, uneven weight or lumpy spots. Restrictive endorsement such as personal or confidential and a postmark different from senders address.

Treatment

In the event of exposure, such a bioterrorist attack a course of antibiotics can prevent the disease from occurring. Anthrax vaccines are used in a high-risk situation, along with prophylactic antibiotics. Before 2001 the first line of treatment for anthrax was penicillin. This is different from terrorist attack because of the concern of genetically engineered penicillin-resistant strains.

Conclusion

Anthrax is a treatable disease if caught early and treated with the right antibiotics. Inhalation anthrax is the most dangerous for, without treatment, only 10-15% of people survive. However, with aggressive treament, 55% of people with Inhalation anthrax survive.

Sources

Moayeri, M., Leppla, S. H., Vrentas, C., Pomerantsev, A. P., & Liu, S. (2015). Anthrax pathogenesis. Annual review of microbiology69, 185-208.

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