Introduction

We’ve heard that anthrax is deadly, but what exactly is it? A bacterial infection caused by spore-bearing bacillus anthracis,¹ found in soil across the world. When the soil is disturbed, it exposes the spores to herbivores or grazing animals. If a person comes into contact with the infected animals or contaminated animal products they can get anthrax from the exposure.

Types of anthrax

Symptoms vary depending on how anthrax enters the body, but all types can lead to death if not treated with antibiotics.

There are four ways anthrax can enter your system:

Cutaneous anthrax 

• Anthrax spores can enter a cut or scrape on the skin when handling an infected animal or contaminated animal products like wool, hide or hair
• On entering the skin, the bacteria can germinate and cause anthrax
• Developing between 1-7 days after initial exposure
• The incubation period is up to 17 days.² 
• Untreated patient mortality is 20% and drops to less than 1% in those treated with antibiotics.³

Inhalation anthrax 

• The deadliest form of anthrax. 
• By inhaling anthrax spores, the spores enter the lungs and accumulate within lung alveoli,  tiny air sacs. They become enveloped by the immune cells, and transported to the lymph nodes (system) 
• Bacteria germinates, multiply and starts producing toxins, resulting in toxin-induced cell damage and cell death, proceeding to bloodstream infection, and leading to septic shock and death⁴ 
• People who work in wool mills, tanneries and slaughterhouses are most susceptible
• The incubation period is between 1-7 days
• Untreated patient mortality was 90% and dropped to 45% with treatment²

Injection anthrax 

• This type is commonly found in intravenous drug users(e.g. heroin), in Europe. With contamination of the drug or needle by spores
• The incubation period between 1-4 days of exposure with a 30% mortality rate⁵ 

Gastrointestinal anthrax 

• Consumption of raw or undercooked meat from an infected animal
• The upper gastrointestinal tract (oesophagus and throat), stomach and intestines are all affected
• Food or drinking water can also be contaminated with spores
• The incubation period is between 1-7 days after eating contaminated meat with the untreated mortality rate, over 50% and less than 40% with treatment

Anthrax meningitis 

• Rare but should be considered in an individual who has a severe headache, altered mental state, meningeal signs or neurological deficits 
• Intracranial bleeding occurs in two-thirds of patients with anthrax meningitis² 
• Anthrax meningitis is fatal, with mortality within 1-6 days after the onset of anthrax.⁶

Symptoms

The symptoms differ between the different types of anthrax¹ 

Cutaneous anthrax 

• Several clustered itchy small blisters
• Massive swelling around the sore
• Painless sore commonly found on the face, neck, arms or hands, and has a black centre

Injection anthrax  

• infected sores that become abscesses deep under the skin at the injection site 
• Extensive bruising forms at the injection site and most patients become septic²

Inhalation anthrax 

• Fever and chills
• Chest pain, cough or shortness of breath
• Heavy sweating
• Confusion or dizziness
• Nausea, vomiting or stomach pains
• Headaches or body aches
• Extreme fatigue 

Gastrointestinal anthrax 

• Fever and chills
• Swelling of neck or neck glands
• Diarrhoea or bloody diarrhoea
• Red eyes and face
• Nausea and vomiting or bloody vomiting
• Sore throat, hoarseness and pain when swallowing
• Stomach pain and swelling
• Fainting

Epidemiology

Since anthrax is a zoonotic disease, meaning it is transmissible from animals to humans, the areas of the world primarily affected are in agricultural regions, such as:

• Sub-Saharan Africa 
• Central and South America
• Central and Southwestern Asia
• Southern and Eastern Europe

Cutaneous anthrax is the most frequently reported type of this disease across the world, accounting for about 95% of human anthrax, whereas inhalational anthrax is 5% and gastrointestinal anthrax is 1%.⁷ 

Diagnosing anthrax

The main tests to establish an anthrax diagnosis are:

• Blood test - measurement of antibodies or toxins
• Test for Bacillus anthracis from any of the following:
  • Skin lesion swab 
  • Cerebrospinal fluid sample 
  • Respiratory secretions

To assist in the diagnosis of inhalation anthrax chest X-rays or CT scans may be used⁸

Treatment

The antibiotics used to treat anthrax are dependent on the type of anthrax. Once exposed to anthrax, oral ciprofloxacin, doxycycline or amoxicillin can be used for post-exposure prophylaxis.

Inhalation or gastrointestinal anthrax should be treated with ciprofloxacin or doxycycline, in patients 12 years old and older, combined with other antibiotics such as rifampicin or vancomycin. 

Cutaneous anthrax should be treated with oral ciprofloxacin or doxycycline, in patients 12 years old and older. Antibiotics are effective against the germinating Bacillus anthracis form but not against dormant spores already inside the body. Therefore, post-prophylaxis treatment should be continued for up to 60 days in combination with administering the vaccine to reduce the threat posed by delayed spore germination.⁹

Antitoxins have also been developed for use with antibiotics, utilising antibodies that target the Bacillus anthrax protective antigen, the main component of the anthrax toxin. Raxibacumab and Obiltoxaximab are human monoclonal antibodies that bind to the antigen, blocking the binding of the toxin to host cells. It is administered intravenously (into a vein) and has shown promising results in animal models for inhalational anthrax in combination with antibiotics.¹⁰ However, antitoxins cannot be used by themselves to treat anthrax, as it does not remove the bacteria and only neutralise the toxins.

Development of anthrax vaccines

Vaccines are an option for individuals who are at an increased risk of coming into contact with the bacteria, but it is not available for the general public. The vaccine is intended to be used as a pre-exposure prophylaxis but can also be used post-exposure.

Two main types of anthrax vaccines have been developed. The first is a cell-free filtrate made of a mixture of components including: 

• Antigenic proteins from cultures of weakened strains of Bacillus anthracis precipitated or adsorbed using an aluminium-based adjuvant. An ingredient to enhance the immune response to the antigen 
• Active ingredient -  Protective antigen that evokes an immune response for creating the antibodies that target this antigen

The vaccines include:

Anthrax vaccine adsorbed (AVA) or BioThrax 

• Containing aluminium hydroxide as the adjuvant. 
• For pre-exposure, this vaccine is administered intramuscularly (into the muscle), in 5 doses for 18 months, followed by annual boosters and can be used with antibiotics. 
• For post-exposure, the CDC recommends 3 subcutaneous doses (into the fatty layer of the skin) for 4 weeks in conjunction with a 60-day course of antibiotics. 

• The AVA anthrax vaccine provides high levels of protection against all types of anthrax, including inhalational anthrax. 
• It has an effectiveness of 93% for people who have completed the course and maintained the booster vaccinations.¹¹

Anthrax vaccine precipitated (AVP)

• This vaccine is licensed in the UK. 
• It consists of anthrax antigens that have been precipitated through aluminium potassium phosphate. 
• This vaccine is administered intramuscularly in 3 injections three weeks apart, and a fourth injection 6 months later, with booster shots administered annually. 

• This is a live attenuated vaccine, which contains live, but weakened Bacillus anthracis spores prepared in a glycerol-saline solution. 
• Examples include the Russian vaccine containing live spores from the weakened attenuated strain of Bacillus Anthracis STI-1 and the Chinese A16R strain of Bacillus anthracis, both administered subcutaneously.¹² 
• Although this vaccine type is effective, it is riskier compared to the non-live vaccines due to the potential to cause the disease.

Safety concerns 

After administration, the following adverse effects have been reported at the injection site: 

• Redness

• Swelling
• Soreness 
• Lump or bruise
• Itching 
• Muscle ache or temporary limitation of movement of the arm where the injection was given¹¹
• Fatigue
• Fever
• Headaches

Patients are advised to contact their healthcare professional if any of the following symptoms occur:

• An allergic reaction or anaphylaxis (emergency)
• High fever
• Dizziness
• Feeling weak

Reasons to not receive the vaccine?

• Those with an allergy to any component of the vaccine
• Those with a weakened immune system as a result of medication or illness
• Previous anthrax infection
• Feeling unwell, wait until fully recovered before getting the vaccine¹¹ 

Summary

• Anthrax is a deadly disease with a high mortality, however, it’s rare and avoidable in humans
• Workers who are at high risk of contracting anthrax should receive the vaccine as pre-exposure and post-exposure prophylaxis 
• The vaccine is effective as protection against both cutaneous and inhalation anthrax