Tularemia, also known as rabbit fever and deer fly fever, is caused by Francisella tularensis, a gram-negative, rod-shaped, intracellular bacterium that is hardy, aerobic, and highly infectious. There are four subspecies of F. tularensis. The infectiousness of these subspecies varies, as does the virulence of the disease they produce in humans. One or more of these subspecies have been found throughout most of North America, Europe, and Asia. The disease is spread via the bites of ticks and deer flies, who pick up bacteria when they bite infected animals. Hunters and taxidermists may also become infected when handling the carcasses of killed, infected animals because the bacteria can be transmitted via the skin. Such an infected animal is known as an animal reservoir, an organism in which a pathogen can replicate, often without causing disease, and that serves as a source of infection for humans.
Plague is an infectious disease caused by the bacillus bacterium Yersinia pestis and has three clinical forms: bubonic, pneumonic, and septicemic. Yersinia pestis is a gram-negative rod-shaped bacterium capable of reproducing in any cell type, including lymphocytes. Bubonic plague is a form of plague in which infection by the virulent bacterium Yersinia pestis spreads through the lymphatic vessels and the lymph nodes swell, forming large, colored nodules called buboes. Septicemic plague form of plague in which the bloodstream is so severely infected by the virulent bacterium Yersinia pestis that tiny clots form throughout the body, potentially causing death by blocking blood vessels and causing organ failure.Pneumonic plague is a form of plague in which the lungs are heavily invaded/infected by the virulent bacterium Yersinia pestis. Bubonic and septicemic plague are spread via the bite of an infected flea that lives on the skin of rats. Rats that live off of human waste foods in urban environments can pass the fleas on to humans, who become infected when the fleas bite. Pneumonic plague can result from septicemic plague or can be passed from person to person when an infected person coughs and/or sneezes aerosolized bacteria into the air. Y. pestis is endemic in many areas of the world, and a vaccine is used to prevent infection in high-risk areas. The severity of outcomes for Y. pestis infections varies depending on the form of plague considered. Bubonic plague is currently the most common disease form resulting from Y. pestis infection but is the least severe in terms of mortality if promptly and properly treated. Most other modern cases of plague occur as pneumonic plague. However, of the three types of plague, the pneumonic form results in the fastest death and highest mortality rates when is not promptly or properly treated with antibiotics such as streptomycin or tetracycline. Septicemic plague has a mortality rate intermediate between that of bubonic or pneumonic plague, but it is much less common than those plague varieties.
Because the spores of B. anthracis are so hardy and the disease they cause is so deadly, they have been identified as a potential biological weapon, an infective agent administered to people in order to intentionally cause disease. In order to counter this, anthrax vaccines have been developed for humans but because of adverse side-effects are not commonly administered to the general population and are inconsistently protective. Individuals at high risk of exposure to B. anthracis, whether natural or weaponized, and individuals suspected to have come in contact with anthrax recently are prescribed the vaccine as a preventive measure. Typical treatment includes the antibiotics penicillin and ciproflaxin and monitoring of a patient’s symptoms to make sure they do not become worse.