Anthrax is an infectious disease caused by the bacteria Bacillus anthracis. The disease can affect both humans and animals although it is more common among livestock and wild animals. The causative bacteria Bacillus anthracis is a spore bearing bacteria and these spores can endure extreme climatic conditions (spores can be found even in Antarctica) for many years, even for decades. These spores are the source of anthrax infection as they can cause the disease after entering the body through inhalation, ingestion or through direct contact with skin lesion.
The disease occurs in herbivorous animals either through inhalation or by direct consumption of the spores during grazing in the wild. Carnivorous animals are infected by consuming the affected herbivorous animals, whereas humans are affected either through direct contact with infected animals (livestock) or by eating the flesh of the infected animals.
There are mainly four forms of anthrax depending upon the route of entry of the anthrax spore; these are cutaneous anthrax (occurring through direct contact with the anthrax spore with broken skin), pulmonary anthrax (occurring through inhalation of spores), gastrointestinal anthrax (occurring through ingestion of anthrax spores) and injection anthrax (occurring through sharing of contaminated needles usually during elicit drugs). Anthrax may lead to death of the affected person.

Causes
Anthrax infection is caused by the spores of the bacteria Bacillus anthracis. Spores are the dormant forms of certain bacteria which can survive in extreme whether conditions and germinates into the bacteria again once there is favorable climatic condition. Infections with the spores have been reported from interment of infected animal’s grave even after 70 years.
The spores of anthrax are soil borne can be found in several countries around the world namely USA, Canada, Eastern part of the Europe, Russia, several countries of Asia and Africa etc. Natural hosts of anthrax include wild and domestic livestock like sheep, cattle, goats, horses etc.
The incidence of the disease is quite rare in the US however it is still occurring in developing countries like Iran, Iraq, Pakistan, countries of sub-Saharan Africa etc.
Infection in the humans usually occurs through contact with the spores either through ingestion, inhalation or direct contact. The disease does not spread from infected persons directly; spores are the source of infection. As such there are other routes of transmission of the diseases; in the US in the year 2001 22 people developed anthrax when they were exposed to anthrax spores sent through mails. 5 of these affected persons ultimately died of anthrax. Again recently 54 cases have been reported in the Europe people contracted anthrax through injection of illegal drugs (heroin); 18 people out of this 54 people died of anthrax. It is thought that the heroin was produced in the area where anthrax is common.
As the spores of anthrax are hardy and can easily be produced outside the natural biological environment (in vitro) like in laboratory, there is high risk of using these spores as biological weapon.

Symptoms
The presenting symptoms of anthrax depend upon the type of anthrax and can thus be categorized into four classes. These are
1. Cutaneous anthrax also known The skin lesions of anthrax usually present with elevated itchy lesions resembling insect bite and the center of the lesion is characteristically black (eschar). The eschar then leads to large typically painless ulceration of the skin with swelling of the adjacent glands (lymph nodes).
2. Gastrointestinal anthrax: Common presenting symptoms include nausea, vomiting, episodes of pain in the abdomen, headache, loss of appetite (anorexia), bloody diarrhea especially in the later stages of the disease, sore throat, difficulty in swallowing, high fever etc.
3. Inhalation or pulmonary anthrax:
Resemble those of other respiratory disease
           a. Sore throat, difficult and painful swallowing, mild degree of fever, tiredness, weakness, generalized body ache, etc.
           b. Chest pain or discomfort
           c. Difficulty in breathing
           d. Nausea
           e. Blood spitting
           f. High degree of fever,
           g. Severe shortness of breathing,
           h. Shock characterized by severe fall in blood pressure, cold, clammy extremities, mental confusion etc due to circulatory collapse may occur.
4. Injection anthrax:
           a. Reddening of the site of injection instead of black discoloration as in cutaneous anthrax (eschar).
           b. Swelling at the site of injection
           c. Multiple organ failure and the patient may also go in shock.
Finally bleeding in the brain may lead to death.