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Overview of Infectious Disease

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Jul 2020| Content last modified Jul 2020
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Microorganisms are tiny living creatures, such as bacteria and viruses. Microorganisms are present everywhere. Despite their overwhelming abundance, relatively few of the thousands of species of microorganisms invade, multiply, and cause disease in people.

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Certain microorganisms have the potential to be used as biological weapons Biological Weapons Biological warfare is the use of microbiological agents as weapons. Such use is contrary to international law and has rarely taken place during formal warfare in modern history, despite the... read more . These microorganisms include those that cause anthrax Anthrax Anthrax is a potentially fatal infection with Bacillus anthracis, a gram-positive, rod-shaped bacteria (see figure How Bacteria Shape Up). Anthrax may affect the skin, the lungs, or, rarely... read more Anthrax , brucellosis Brucellosis Brucellosis is an infection caused by several species of the gram-negative bacteria Brucella and characterized by fever and bodywide symptoms. Brucellosis is acquired mainly by having contact... read more , hemorrhagic fever (Ebola virus infection Ebola Virus and Marburg Virus Infections Marburg and Ebola virus infections cause bleeding and organ malfunction. These infections often result in death. Marburg and Ebola infections are spread through handling live or dead infected... read more and Marburg virus infection Ebola Virus and Marburg Virus Infections Marburg and Ebola virus infections cause bleeding and organ malfunction. These infections often result in death. Marburg and Ebola infections are spread through handling live or dead infected... read more ), plague Plague and Other Yersinia Infections Plague is a severe infection caused by the gram-negative bacteria Yersinia pestis and often involving the lymph nodes and/or lungs. The bacteria are spread mainly by the rat flea. Depending... read more Plague and Other Yersinia Infections , smallpox Smallpox Smallpox is a highly contagious, very deadly disease caused by the variola virus. The disease is now considered eliminated. There have been no cases of smallpox since 1977. People can acquire... read more Smallpox , and tularemia Tularemia Tularemia is infection that is caused by the gram-negative bacteria Francisella tularensis, which is acquired when people have direct contact with infected wild animals, usually rabbits, or... read more Tularemia and those that produce botulinum toxin. Each of the diseases is potentially fatal and, except for anthrax, botulism, and tularemia, can be passed from person to person. Direct person-to person transmission of brucellosis is extremely rare.

Effects of Infection

Infections may affect only part of the body (a local infection) or the whole body (a systemic infection). Abscesses and urinary bladder infections are examples of local infections. Severe systemic infections may have life-threatening effects, such as sepsis or septic shock Sepsis and Septic Shock Sepsis is a serious bodywide response to bacteremia or another infection plus malfunction or failure of an essential system in the body. Septic shock is life-threatening low blood pressure ... read more .

Most effects resolve when the infection is effectively treated.

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Ebola Virus and Marburg Virus Infections
Ebola and Marburg virus infections are extremely serious and frequently fatal. Like other viruses in the class known as filoviruses, Ebola and Marburg infections cause extensive bleeding. Which of the following statements about Ebola and Marburg infections is NOT correct?
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