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Salmonella typhi is a bacterium. It lives in the intestinal tracts of many animals, and contamination of food or water by this bacterium in fecal matter transmits the disease typhoid. Typhoid is a potentially lethal disease and has a history of causing fevers in people living in countries with poor sanitation.
Many different types of disease are caused by Salmonella bacteria. Historically, each type of disease and the causative strain received a different species name. For example, Salmonella typhi causes typhoid in humans, and Salmonella typhimurium causes food-borne illness in humans and a typhoid-like disease in mice. Now, however, most of the pathogenic Salmonella bacteria that previously were a species unto themselves now form a part of the Salmonella enterica species.
As part of the Salmonella enterica species, S. typhi is one serovar of the of the S. enterica species. Each serovar has its own specific antigen profile compared to others in the subspecies. Therefore, S. typhi may also be more accurately referred to as the Salmonella enterica subspecies enterica serovar Typhi. Doctors generally take a shortcut and use the old name of S. typhi to refer to the bacterium.
S. typhi can live in the intestinal tract of animals with cold blood, like reptiles, and those that are warm blooded, like humans. The bacterium is very similar to Escherichia coli, a very common intestinal microbe. Salmonella typhi can survive in environments with or without oxygen and is shaped like a rod.
Typhoid fever is a disease that is caused by ingesting food or drink that is contaminated with fecal matter containing the bacterium. If the bacterium makes its way past the host's gastrointestinal defenses, it can then get into the bloodstream. Headaches, fever, and a lack of appetite result. Sometimes, the affected person displays a spotted rash but not always. Although typhoid can be lethal, immediate antibiotic treatment can resolve the condition.
The bacterium was first noticed to be present in cases of typhoid in the late 1800s. Before then, many different forms of gastrointestinal illnesses with fever were included under the name typhoid. The most famous case of typhoid was at the beginning of the 20th century, when a cook called Mary Mallon picked up the disease and became a symptomless carrier.
She then infected many people through contamination of food with the Salmonella typhi she carried in her intestinal tract. Typhoid Mary, as she became known, eventually had to be locked up in New York to stop her working as a cook and endangering the lives of the people she cooked for. Although typhoid is rare in countries with good sanitation, it still infects people in poorer countries that lack adequate sanitation infrastructure.