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The term rickettsiosis, or rickettsial disease, is used to describe several types of diseases caused by different bacterial infections, and with varying symptoms ranging from relatively mild to very severe. Examples of rickettsial diseases are epidemic and endemic typhus and Rocky Mountain spotted fever. Different types of rickettsiosis are caused by different species of bacteria, mainly belonging to the genus Rickettsia, and they are transmitted to humans by fleas, ticks, mites, or lice. Common symptoms of rickettsiosis include fever, headache, gastrointestinal problems, skin rash, skin lesions, joint pain, and muscle pain. Treatment varies depending on the specific disease and often includes antibiotics and steroids.
Based on certain characteristics of the bacteria causing infection, rickettsial diseases are often divided into the spotted fever group and the typhus group, though some disease experts disagree with this classification. The bacteria causing rickettsial disease were first discovered in 1909 by Howard Ricketts, an American scientist, and are named after him. All bacteria causing rickettsiosis are intracellular bacteria, meaning they live inside the cells of the body. These bacteria have traits that make the infections they cause difficult to diagnose with standard medical tests, such as blood tests, and diagnosis is often based on observation of symptoms rather than laboratory analysis.
Humans are usually infected with rickettsiosis when they are bitten by ticks or mites that carry Rickettsia bacteria or by inhaling the feces of infected lice or fleas. Depending on what disease the specific species of bacteria causes, it can take from one to three weeks before an infected person shows any symptoms. Some rickettsial diseases like epidemic typhus, scrub typhus, and Rocky Mountain spotted fever, have very severe symptoms and a high fatality rate. Others, such as endemic typhus and rickettsialpox, have only mild to moderate symptoms and rarely cause death.
Rickettsial diseases occur globally, but some species of bacteria are found only in particular regions, meaning that the infections they cause occur only there. For example, scrub typhus does not occur in America, and some types of spotted fever are only found in specific countries or continents like Japan, Australia, or Africa. However, the two most well-known types of rickettsiosis, endemic typhus and epidemic typhus, are found all over the world.
Prevention of rickettsiosis is mainly focused on removing the organisms that transmit infection to humans. Good general hygiene, delousing, removing ticks, and using tick repellent is recommended. Rodent control is also considered important, because infected fleas often live on rodents before they are transmitted to humans.