Anthrax

What is Anthrax?

Anthrax is a rare and potentially fatal infectious disease. The pathogen responsible for it is a bacterium known as Bacillus anthracis. Often, it is herbivores like common livestock animals that tend to suffer from anthrax, although it is not unheard of in other animals. Humans acquire the pathogen either through contact with infected animals or through contact with or ingestion of contaminated animal products. Those who exhibit the symptoms of anthrax are at a risk of developing pneumonia or sepsis and may even die.

What Causes It?

When it is present within a living body, often that of a livestock animal such as a cow, sheep or goat, the bacterium is active and can multiply. When these bacteria are shed from the body of the infected animal and come into contact with the external environment, they turn into spores. A bacterial spore is the inactive state of the bacterium. In this form, the bacterium does not present a threat. These spores can persist in the soil for extended periods of time since they are resilient and capable of surviving high temperatures and extreme environmental conditions. They can even survive radiation up to a certain extent. When they re-enter living bodies of animals or humans either through contact, inhalation or ingestion, these spores become reactivated and the bacteria will once again have the potential to give rise to disease.

How Do Humans Acquire This Disease?

The mechanisms of transmission of anthrax are not very well understood. However, certain broad patterns are clearly identifiable. Cases of anthrax in humans occur through three potential pathways. These are the cutaneous, oral (ingestion) and inhalational pathways of exposure. In other words, you could potentially acquire the bacterium by touching the source of contamination, eating contaminated material or breathing in airborne spores. Cutaneous exposure accounts for the majority of anthrax cases in humans. It generally occurs when anthrax spores enter the body through cuts, breaks or sores in the skin, often while interacting with infected animals or handling contaminated animal parts such as hides or bones. Cutaneous anthrax may also be transmitted through insect bites and flies are often implicated in large-scale outbreaks of the disease.

How Do Symptoms Arise After Exposure?

Symptoms do not manifest immediately upon exposure. The space of time between exposure and onset of symptoms is called the incubation period. Once within the body, the bacterium becomes active and displays an ingenious method of circumventing the body’s natural defenses. Normally, macrophages (a type of white blood cell) are responsible for clearing away foreign matter, cellular debris, and pathogens. They do this by engulfing the foreign matter and breaking it down. This process is known as phagocytosis. The anthrax bacterium produces a polypeptide capsule that allows it to avoid being disabled by means of phagocytosis. Further, the bacterium produces substances called endotoxins that give rise to symptoms of the disease.

What Are The Different Types of Anthrax And Their Respective Symptoms?

Not all cases of anthrax exposure necessarily end up in symptomatic disease. According to the World Health Organisation, humans generally display a moderate level of resistance to this microbe. There are three major routes by which the bacterium can invade a human body. The nature of symptoms depends on which of these pathways is involved. These are discussed below.

• Cutaneous Anthrax. This is the most common form of anthrax in humans. In such instances, the incubation period can vary from as little as a few hours to about 3 weeks from the date of exposure. Typically, exposed stretches of skin will develop swelling and lesions where the tissue has suffered damage as a result of necrosis. Endotoxins released by the bacteria are responsible for causing tissue necrosis. This can be treated effectively by means of antibiotics if caught early enough. Otherwise, the disease can be fatal.
• Pulmonary Anthrax as a result of exposure via inhalation. In such cases, it may be about 4 to 6 days before onset of symptoms but it could also take as long as 10 days for this to occur. In the initial stages of the disease, symptoms are rather non-specific and can mimic those of influenza. The patient will normally exhibit symptoms such as fever or chills, headache, cough, sweats, muscle aches and weakness. As the disease progresses, patients may also experience nausea or vomiting, diarrhea and mental confusion. An excess of fluid could potentially build up between the pleural membranes and the lungs, affecting the patient’s ability to breathe. Eventually, the bacteria spill over into the bloodstream at which point the patient could develop potentially life-threatening blood poisoning.
• Oropharyngeal symptoms due to ingestion of spores. This is one potential outcome of oral exposure through ingestion of spores present in contaminated meat. The patient will develop lesions that remain largely localized to the oral cavity or pharyngeal wall. Other symptoms include a sore throat, difficulty in swallowing and lymphadenopathy. As the disease worsens, the patient will likely develop a swollen neck and the chest wall may also be affected similarly.
• Gastrointestinal Anthrax as a result of ingestion of spores. Again, this form of disease develops as a consequence of eating insufficiently cooked or contaminated meat from an infected animal. The incubation period ranges from a few days to a week. As the name suggests, the main site to be affected is the digestive system and lesions can develop anywhere along the length of the gastrointestinal tract. Hence, the patient will exhibit fever, vomiting, and diarrhea. As the disease advances, the patient may also notice blood in the watery stools. There is a high risk of the bacteria subsequently invading the bloodstream and setting off a widespread inflammatory response giving rise to sepsis.

What Are The Possible Complications?

If diagnosed early enough, it is possible to treat the patient effectively with antibiotics. However, in the event that the disease escalates, there can be a number of severe complications. For one, the patient may develop meningitis. As a result, he or she may display a high fever, vomiting and altered mental state. Another potential critical outcome is blood poisoning or sepsis. This happens because of an immune reaction to the presence of bacteria in the bloodstream. This can lead to organ failure, coma and death if it is not treated promptly. Delay in obtaining a correct diagnosis is more likely in instances of non-cutaneous disease. Hence, the associated risk of mortality is high in such cases.   

How Is It Diagnosed?

Since the symptoms vary as per the specific variant of the disease, the necessary means of diagnosis will typically vary. However, in all instances, the patient will be asked for their medical history and a description of symptoms from the time of the first onset. In the case of cutaneous disease, the presentation is difficult to differentiate from that of more common conditions. Similarly, early signs of both pulmonary and gastrointestinal disease are rather non-specific. If the physician suspects anthrax, it would be necessary to determine the mode of exposure. Culturing samples of fluid obtained from skin lesions help to clarify the identity of the pathogen. Similarly, stool, blood, sputum, pulmonary effusions or even cerebrospinal fluid will need to be examined as the case may be. Diagnostic imaging of areas such as the chest, brain and GI tract will help identify complications such as pleural effusion and meningitis.

Treatment & Prevention

An antibiotic course for around 2 months (60 days) is considered to be the standard treatment for anthrax. The antibiotic course comprises drugs such as doxycycline or ciprofloxacin.

The choice of drugs mainly depends on the factors such as the patient’s age, mode of infection, overall health etc. Infection treated promptly usually has a good outlook.

Some cases of advanced inhalation anthrax do not respond to antibiotics as the number of toxins produced exceeds the amount that the drugs can successfully eliminate.

• Antitoxin therapies- Focused research on antitoxin therapies initiated after the 2001 anthrax attacks in the United States. The antitoxin therapy aims at eliminating the toxins rather than killing the bacteria. These medications are still being studied.
• Surgical intervention– Surgical removal of the infected tissue was done in some of the cases where patients got the infection by an injection.

As per the information furnished by the World Health Organization, a vaccine is available to prevent the anthrax infection. However, meticulous testing of the vaccine in human trials has not yet been done. In some cases, the vaccine is given to an individual who might contract occupational exposure to the infection (such as military personnel, tannery workers etc.). The vaccine is unavailable for the purpose of mass immunization.

Prevention of the anthrax infection can be done through vaccination in the individuals at the risk of exposure to the bacteria. 3 doses of the vaccine are required.

Avoiding contact with livestock and animal skin in endemic regions is important to prevent the spread of the infection.

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