The bacterium Salmonella Typhi causes the infectious disease typhoid fever. It is a pathogenic enterobacterium that has a high probability of causing disease. An infectious dose of 100 to 1000 pathogens is already sufficient. The rate of disease increases with the number of pathogens. Infection occurs primarily through humans.
What is Salmonella Typhi?
Salmonella Typhi is a pathogenic bacterium. It can be transmitted by people who are already ill or by so-called permanent carriers. These are ill persons in whom the bacterium can be detected for at least ten weeks. Typhoid fever may also be triggered by the consumption of contaminated food, such as fertilized fruit and vegetables, mussels and oysters. Unclean water and fly droppings are also possible carriers. Salmonella Typhi exclusively affects humans and has an incubation period of seven to twenty days. Infection with this pathogen is reportable. If it has been ingested with food, the bacterium enters the bloodstream via the lymphatic system. Thus, typhoid fever can travel to all organs (systemic disease). If typhoid fever is not treated, the disease is very dangerous and can be fatal.
Occurrence, distribution, and characteristics
Salmonella Typhi belongs to the rod-shaped bacterial genus Salmonella and, in turn, to the Enterobacteriaceae family. Salmonellae are multiply actively motile and usually do not form spores. Their distribution is worldwide. Many types of salmonellae are also found in animals at the same or different temperatures as well as in special habitats far from living organisms. Very often, infection occurs through contaminated or stagnant water as well as food. Salmonella particularly colonize eggs and poultry meat. Diseases caused by salmonellae (salmonelloses) are generally notifiable in Germany. The number of cases has declined significantly in recent decades. It is estimated that every fifth person in Germany is a carrier of salmonella. Worldwide, the number of typhoid fever cases is estimated at around 16 million per year. People in developing countries are almost exclusively affected. In this context, it is assumed that about 500,000 people die each year. Salmonella can survive for several weeks under relatively extreme conditions. In dried excrement, they can be detected for more than two and a half years. Only strong sunlight and high heat can cause them to die. Heating food to 75 °C for a period of at least ten minutes can relatively reliably prevent infection by Salmonella. Freezing food generally does not kill the bacteria. Suitable disinfectants, on the other hand, can destroy the pathogens in a few minutes. Salmonella Typhi is common in both temperate and subtropical areas. Among those who do not receive treatment, an estimated ten percent remain permanent carriers for an extended period of time. They shed typhoid pathogens with their stool or urine for up to three months. This can even occur over a period of more than a year if the bacteria persist in the gallbladder and bile ducts. The presence of gallstones may further promote these permanent excretions. Many of the persistent excretors do not show the typical signs of illness, but they can infect other people very easily.
Diseases and symptoms
In the 1st week of a typhoid fever illness, the so-called stage incrementi, headache, nausea and fever occur. This may rise to a level of 41°C. The heartbeat may drop to less than 60 beats per minute (bradycardia). The white blood cell (leukocyte) count in the blood may drop well below normal. This is often accompanied by constipation. Bowel movements occur less frequently during this time. In the subsequent stage acmes (2nd to 3rd week), the pathogen reaches other organs via the bloodstream. For example, the spleen may enlarge (splenomegaly). The small-spotted, red roseolae form on the skin, and the characteristic, swelling typhomas form in the intestine. Salmonella Typhi can then be detected in the stool. The fever moves steadily at about 40 °C during this phase. The frequency of bowel movements increases markedly, and the consistency becomes mushy. The patient is seized with a permanent dizziness. In the 4th to 5th week, the decrementi stage follows, in which the symptoms of the disease usually decrease.However, bleeding in the digestive tract and severe inflammation of the peritoneum are possible and require decisive medical action. Typhoid infection is usually treated with antibiotics. For this purpose, samples of stool and blood are evaluated to rule out resistance of the pathogen to the antibiotic agents commonly used. The best prophylaxis against Salmonella Typhi is attentive and thorough hygiene. It is advisable to strictly adhere to the avoidance of questionably prepared food and tap water whenever traveling to tropical and subtropical areas. Vaccination programs against typhoid fever have been proven for decades and are implemented with both live and inactivated vaccines. The live vaccine uses Salmonella typhi bacteria, which have a non-disease-causing effect and stimulate the immune system to produce antibodies. The vaccine is well tolerated and gives effective protection in endemic areas for about one year. For repeated travel, booster vaccination is advised after one year. In most cases, the inactivated vaccine consists of a polysaccharide, which also controls antibody formation. Here, protection against typhoid fever can even be expected for three years.
