What causes typhoid fever? Be careful of bacteria and viruses!

Typhoid fever, also known as enteric fever, is a common acute intestinal infectious disease in clinical practice. Many people do not know what causes typhoid fever. In this case, it is generally closely related to typhoid Salmonella infection. The patient's own immunity is low, which can easily lead to bacterial infection, thus causing typhoid fever.

1. The amount of bacteria infected:

When Salmonella typhi enters the digestive tract through the mouth, it can usually be killed by stomach acid. However, if the invading bacteria are large in number, or the defense barrier functions such as gastric acid secretion and normal intestinal flora are damaged, Salmonella typhi can enter the small intestine and invade the intestinal mucosa.

2. Virulence of the strain:

Endotoxins released by Salmonella typhi play an important role in the pathological process of typhoid fever. However, studies have shown that clinical phenomena such as persistent fever and toxic blood symptoms in typhoid patients are not directly caused by endotoxemia. The actual reasons are far more complicated than simple endotoxemia. Endotoxins enhance the inflammatory response of local lesions, activate monocytes-macrophages and neutrophils, causing them to produce and release various cytokines, and the toxic substances produced by necrotic tissue may be closely related to the clinical manifestations of typhoid fever. In addition, endotoxins of Salmonella typhi can also induce DIC or hemolytic uremic syndrome, the latter of which is a clinical syndrome caused by intravascular coagulation limited to the kidneys.

3. The body's immune status:

After the fourth week of the disease, the human body's various immune capabilities gradually strengthen, especially the cellular immunity. The typhoid bacilli gradually disappear from the blood and organs, the intestinal wall ulcers gradually heal, the clinical manifestations gradually recover, and the disease is finally cured. A small number of patients may have insufficient immunity, and the pathogens that have not been eliminated in the latent lesions may multiply again, invade the blood circulation and cause relapse. The main pathological feature of typhoid fever is the systemic mononuclear-macrophage system (including liver, spleen, bone marrow, lymphoid tissue, etc.), the proliferative reaction of monocytes and macrophages, forming "typhoid nodules". The lesions are most prominent in the intestines, especially the terminal ileum. The pathological process includes four stages: hyperplasia, necrosis, ulcer formation, and ulcer healing.