anthrax anthrax anthrax is an infection caused by the bacterium bacillus anthracis. it can occur in four forms: skin, lungs, intestinal, and injection. symptom onset occurs between one day and more than two months after the infection is contracted. the skin form presents with a small blister with surrounding swelling that often turns into a painless ulcer with a black center. the inhalation form presents with fever, chest pain and shortness of breath. the intestinal form presents with diarrhea (which may contain blood), abdominal pains, nausea and vomiting. the injection form presents with fever and an abscess at the site of drug injection. for its use in biological warfare, see anthrax weaponization. anthraxa skin lesion with black eschar characteristic of anthraxspecialtyinfectious diseasesymptomsskin form: small blister with surrounding swellinginhalational form: fever, chest pain, shortness of breathintestinal form: nausea, vomiting, diarrhea, abdominal paininjection form: fever, abscessusual onset1 day to 2 months post contactcausesbacillus anthracisrisk factorsworking with animals, travelers, postal workers, military personneldiagnostic methodbased on antibodies or toxin in the blood, microbial culturepreventionanthrax vaccination, antibioticstreatmentantibiotics, antitoxinprognosis20–80% die without treatmentfrequency>2,000 cases per year according to the centers for disease control and prevention in the united states, the first clinical descriptions of cutaneous anthrax were given by maret in 1752 and fournier in 1769. before that anthrax had been described only through historical accounts. the prussian scientist robert koch (1843–1910) was the first to identify bacillus anthracis as the bacterium that causes anthrax. anthrax is spread by contact with the bacterium's spores, which often appear in infectious animal products. contact is by breathing or eating or through an area of broken skin. it does not typically spread directly between people. risk factors include people who work with animals or animal products, travelers, and military personnel. diagnosis can be confirmed by finding antibodies or the toxin in the blood or by culture of a sample from the infected site. anthrax vaccination is recommended for people at high risk of infection. immunizing animals against anthrax is recommended in areas where previous infections have occurred. a two-month course of antibiotics such as ciprofloxacin, levofloxacin and doxycycline after exposure can also prevent infection. if infection occurs, treatment is with antibiotics and possibly antitoxin. the type and number of antibiotics used depend on the type of infection. antitoxin is recommended for those with widespread infection. a rare disease, human anthrax is most common in africa and central and southern asia. it also occurs more regularly in southern europe than elsewhere on the continent and is uncommon in northern europe and north america. globally, at least 2,000 cases occur a year, with about two cases a year in the united states. skin infections represent more than 95% of cases. without treatment the risk of death from skin anthrax is 23.7%. for intestinal infection the risk of death is 25 to 75%, while respiratory anthrax has a mortality of 50 to 80%, even with treatment. until the 20th century anthrax infections killed hundreds of thousands of people and animals each year. anthrax has been developed as a weapon by a number of countries. in herbivorous animals infection occurs when they eat or breathe in the spores while grazing. animals may become infected by killing and/or eating infected animals. etymology the english name comes from anthrax (ἄνθραξ), the greek word for coal, possibly having egyptian etymology, because of the characteristic black skin lesions developed by people with a cutaneous anthrax infection. the central black eschar surrounded by vivid red skin has long been recognised as typical of the disease. the first recorded use of the word "anthrax" in english is in a 1398 translation of bartholomaeus anglicus' work de proprietatibus rerum (on the properties of things, 1240). anthrax was historically known by a wide variety of names indicating its symptoms, location and groups considered most vulnerable to infection. they included siberian plague, cumberland disease, charbon, splenic fever, malignant edema, woolsorter's disease and la maladie de bradford. signs and symptoms skin skin lesion from anthrax skin anthrax lesion on the neck cutaneous anthrax, also known as hide-porter's disease, is when anthrax occurs on the skin. it is the most common form (>90% of anthrax cases). it is the least dangerous form (low mortality with treatment, 23.7% mortality without). cutaneous anthrax presents as a boil-like skin lesion that eventually forms an ulcer with a black center (eschar). the black eschar often shows up as a large, painless, necrotic ulcer (beginning as an irritating and itchy skin lesion or blister that is dark and usually concentrated as a black dot, somewhat resembling bread mold) at the site of infection. in general, cutaneous infections form within the site of spore penetration between two and five days after exposure. unlike bruises or most other lesions, cutaneous anthrax infections normally do not cause pain. nearby lymph nodes may become infected, reddened, swollen, and painful. a scab forms over the lesion soon, and falls off in a few weeks. complete recovery may take longer. cutaneous anthrax is typically caused when b. anthracis spores enter through cuts on the skin. this form is found most commonly when humans handle infected animals and/or animal products. injection in december 2009, an outbreak of anthrax occurred among injecting heroin users in the glasgow and stirling areas of scotland, resulting in 14 deaths. the source of the anthrax is believed to have been dilution of the heroin with bone meal in afghanistan. injected anthrax may have symptoms similar to cutaneous anthrax, with the exception of black areas, and may also cause infection deep into the muscle and spread faster. this can cause it to be harder to recognise and treat. lungs inhalation anthrax usually develops within a week after exposure, but may take up to 2 months. during the first few days of illness, most people have fever, chills, and fatigue. these symptoms may be accompanied by cough, shortness of breath, chest pain, and nausea or vomiting, making inhalation anthrax difficult to distinguish from influenza and community-acquired pneumonia. this is often described as the prodromal period. over the next day or so, shortness of breath, cough, and chest pain become more common, and complaints not involving the chest such as nausea, vomiting, altered mental status, sweats, and headache develop in one-third or more of people. upper respiratory tract symptoms occur in only a quarter of people, and muscle pains are rare. altered mental status or shortness of breath generally brings people to healthcare and marks the fulminant phase of illness. it infects the lymph nodes in the chest first, rather than the lungs themselves, a condition called hemorrhagic mediastinitis, causing bloody fluid to accumulate in the chest cavity, thereby causing shortness of breath. the second (pneumonia) stage occurs when the infection spreads from the lymph nodes to the lungs. symptoms of the second stage develop suddenly within hours or days after the first stage. symptoms include high fever, extreme shortness of breath, shock, and rapid death within 48 hours in fatal cases. gastrointestinal gastrointestinal (gi) infection is most often caused by consuming anthrax-infected meat and is characterized by diarrhea, potentially with blood, abdominal pains, acute inflammation of the intestinal tract, and loss of appetite. occasional vomiting of blood can occur. lesions have been found in the intestines and in the mouth and throat. after the bacterium invades the gastrointestinal system, it spreads to the bloodstream and throughout the body, while continuing to make toxins. cause bacteria photomicrograph of a gram stain of the bacterium bacillus anthracis, the cause of the anthrax disease main article: bacillus anthracis bacillus anthracis is a rod-shaped, gram-positive, obligate aerobe bacterium about 1 by 9 μm in size. it was shown to cause disease by robert koch in 1876 when he took a blood sample from an infected cow, isolated the bacteria, and put them into a mouse. the bacterium normally rests in spore form in the soil, and can survive for decades in this state. herbivores are often infected while grazing, especially when eating rough, irritant, or spiky vegetation; the vegetation has been hypothesized to cause wounds within the gastrointestinal tract, permitting entry of the bacterial spores into the tissues. once ingested or placed in an open wound, the bacteria begin multiplying inside the animal or human and typically kill the host within a few days or weeks. the spores germinate at the site of entry into the tissues and then spread by the circulation to the lymphatics, where the bacteria multiply. the production of two powerful exotoxins and lethal toxin by the bacteria causes death. veterinarians can often tell a possible anthrax-induced death by its sudden occurrence, and by the dark, nonclotting blood that oozes from the body orifices. most anthrax bacteria inside the body after death are outcompeted and destroyed by anaerobic bacteria within minutes to hours post mortem. however, anthrax vegetative bacteria that escape the body via oozing blood or through the opening of the carcass may form hardy spores. these vegetative bacteria are not contagious. one spore forms per one vegetative bacterium. the triggers for spore formation are not yet known, though oxygen tension and lack of nutrients may play roles. once formed, these spores are very hard to eradicate. the infection of herbivores (and occasionally humans) by the inhalational route normally begins with inhaled spores being transported through the air passages into the tiny air sacs (alveoli) in the lungs. the spores are then picked up by scavenger cells (macrophages) in the lungs and are transported through small vessels (lymphatics) to the lymph nodes in the central chest cavity (mediastinum). damage caused by the anthrax spores and bacilli to the central chest cavity can cause chest pain and difficulty breathing. once in the lymph nodes, the spores germinate into active bacilli that multiply and eventually burst the macrophages, releasing many more bacilli into the bloodstream to be transferred to the entire body. once in the bloodstream, these bacilli release three proteins named lethal factor, edema factor, and protective antigen. the three are not toxic by themselves, but their combination is incredibly lethal to humans. protective antigen combines with these other two factors to form lethal toxin and edema toxin, respectively. these toxins are the primary agents of tissue destruction, bleeding, and death of the host. if antibiotics are administered too late, even if the antibiotics eradicate the bacteria, some hosts still die of toxemia because the toxins produced by the bacilli remain in their systems at lethal dose levels. bacillus anthracis color-enhanced scanning electron micrograph shows splenic tissue from a monkey with inhalational anthrax; featured are rod-shaped bacilli (yellow) and an erythrocyte (red) gram-positive anthrax bacteria (purple rods) in cerebrospinal fluid: if present, a gram-negative bacterial species would appear pink. (the other cells are white blood cells.) exposure the spores of anthrax are able to survive in harsh conditions for decades or even centuries. such spores can be found on all continents, including antarctica. disturbed grave sites of infected animals have been known to cause infection after 70 years. historically, inhalational anthrax was called woolsorters' disease because it was an occupational hazard for people who sorted wool. today, this form of infection is extremely rare in advanced nations, as almost no infected animals remain. occupational exposure to infected animals or their products (such as skin, wool, and meat) is the usual pathway of exposure for humans. workers who are exposed to dead animals and animal products are at the highest risk, especially in countries where anthrax is more common. anthrax in livestock grazing on open range where they mix with wild animals still occasionally occurs in the united states and elsewhere. many workers who deal with wool and animal hides are routinely exposed to low levels of anthrax spores, but most exposure levels are not sufficient to develop anthrax infections. a lethal infection is reported to result from inhalation of about 10,000–20,000 spores, though this dose varies among host species. little documented evidence is available to verify the exact or average number of spores needed for infection. mode of infection inhalational anthrax, mediastinal widening anthrax can enter the human body through the intestines (ingestion), lungs (inhalation), or skin (cutaneous) and causes distinct clinical symptoms based on its site of entry. in general, an infected human is quarantined. however, anthrax does not usually spread from an infected human to an uninfected human. if the