Bacteria Photomicrograph of a Gram stain of the bacterium Bacillus<unk> is, the cause of the<unk>  disease Bacillus<unk> is is a rod-shaped, Gram-positive, facultative anaerobic 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 GI tract, permitting entry of the bacterial spores into the tissues, though this has not been proven. 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<unk> -induced death by its sudden occurrence, and by the dark, nonclotting blood that oozes from the body orifices. Most<unk>  bacteria inside the body after death are outcompeted and destroyed by anaerobic bacteria within minutes to hours post mortem. However,<unk>  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<unk>  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. File:Bacillus<unk> is.Bacillus<unk> is File:Anthrax color enhanced micrograph.Color-enhanced scanning electron micrograph shows splenic tissue from a monkey with inhalational<unk> ; featured are rod-shaped bacilli (yellow) and an erythrocyte (red) File:Gram Stain<unk> .Gram-positive<unk>  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<unk>  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<unk>  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<unk>  is more common.<unk>  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<unk>  spores, but most exposure levels are not sufficient to develop<unk>  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 mediastinal widening<unk>  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,<unk>  does not usually spread from an infected human to an uninfected human. If the disease is fatal to the person's body, though, its mass of<unk>  bacilli becomes a potential source of infection to others and special precautions should be used to prevent further contamination. Inhalational<unk> , if left untreated until obvious symptoms occur, is usually fatal.<unk>  can be contracted in laboratory accidents or by handling infected animals, their wool, or their hides. It has also been used in biological warfare agents and by terrorists to intentionally infect as exemplified by the 2001<unk>  attacks.
Anthrax
Plague 
Spanish flu
Rubella
Metal fume fever
Great Plague of London
Trench fever
Scrub typhus