Typhoid Meaning Etiology Pathogenesis


Typhoid Etiology and Pathogenesis

Meaning of Typhoid: Typhoid fever is an acute infectious disease caused by typhoid. The lesion is characterized by the proliferation of cells in the whole body monocyte macrophage system. The lesions in the lymphatic tissue at the terminal ileum were the most prominent. The main clinical manifestations are persistent fever, symptoms of neurotoxicity and gastrointestinal symptoms, relative slowness, splenomegaly, skin roseola and reduction of neutrophils and eosinophils. Sometimes serious complications such as intestinal bleeding and intestinal perforation can occur.

Etiology and pathogenesis

 Group D in the genus Salmonella typhi, Gram-negative. Its bacterial "O" antigen, flagella "H" antigen and "Vi" antigen on the surface can cause the body to produce corresponding antibodies, especially "O" and "H" antigens are strong, so serum agglutination test (fat response), Widal Reaction) to determine the increase in antibodies in serum, can be used as a basis for clinical diagnosis of typhoid fever. Endotoxin released during bacterial lysis is the main cause of disease.

Typhoids or carriers are the source of the disease. Bacteria are excreted with feces and urine, contaminate food, drinking water, milk, etc., or infect the alimentary canal through flies. It is more common in children and young adults. Onset can occur throughout the year, with the most in summer and autumn. After the illness, a relatively stable immunity can be obtained, and rarely reinfected.

Typhoid bacteria are mostly destroyed in the stomach. Whether or not the disease mainly depends on various factors such as the amount of bacteria reaching the stomach.

When the amount of infected bacteria is large (105), the bacteria can enter the small intestine through the small intestinal mucosal epithelial cells and invade the lymphatic tissue of the intestinal wall, especially the collective lymph nodes or solitary lymph nodes at the end of the ileum. And along the lymphatic vessels to reach the mesenteric lymph nodes.

Typhoid bacteria in lymphoid tissues are engulfed by macrophages, grow and reproduce in them, and can enter the blood through the chest duct, causing bacteremia.

Bacteria in the blood are quickly swallowed by the cells of the whole body mononuclear macrophage system, and multiply in them, causing enlargement of the liver, spleen, and lymph nodes.
During this period, the patient has no clinical symptoms, so it is called the incubation period, which is about 10 days. Thereafter, as the bacteria multiply and the endotoxin is released into the bloodstream again, the patient develops symptoms of sepsis and toxemia.

Because a large amount of typhoid bacteria in the gallbladder enters the intestine again with bile, it repeatedly invades the sensitized lymphoid tissue, causing it to have a strong allergic reaction, causing intestinal mucosal necrosis, shedding and ulcer formation.

Typhoid Pathology

Typhoid Pathological changes and clinicopathological connections

The inflammation caused by typhoid bacteria is an acute proliferative inflammation characterized by macrophage proliferation. When hyperplasia is active, typhoid bacteria, red blood cells, and cell debris are phagocytosed in the macrophage cytoplasm, and the role of phagocytosis of red blood cells is particularly obvious.

This macrophage is called typhoid. Typhoid cells often aggregate into clusters and form small nodules called typhoid granuloma or typhoid nodule. They are characteristic lesions of typhoid and have pathological diagnostic value.

Typhoid granuloma

Intestinal lesions

Typhoid intestinal lesions are the most common and obvious lesions in the lower ileum and solitary lymph nodes. According to the development process of the disease, it is divided into four stages, and each stage lasts about one week.

(1) Myeloid swelling period:

In the first week of onset, the lymph tissue in the lower ileum is slightly swollen, bulging on the surface of the mucosa, gray-red, soft. The surface of the raised tissue resembles the sulcus of the brain, and the collective lymph nodes are most typical.

(2) Necrosis period

Occurred in the second week after the onset of the disease, and local intestinal mucosal necrosis of the lesion was caused by various reasons.

(3) Ulcer stage

ulcers are formed after the mucous membrane of necrotic intestine is shed. The edge of the ulcer is raised and the bottom is uneven. The major axis of ulcers in the collective lymph nodes is parallel to the major axis of the intestine. The ulcers in the solitary lymph nodes are small and round.

Ulcers are usually deep and submucosal, and severe necrosis can reach the muscle layer and serosa layer, and even perforation, such as invasion of small arteries, can cause severe bleeding. This period usually occurs in the third week of onset.

(4) Healing period

This is equivalent to the fourth week of onset. The granulation tissue of the ulcer filled it with hyperplasia, and the epithelium of the edge of the ulcer regenerated and covered and healed.
Typhoid Intestinal Disease A: Myeloid swelling, B: Necrotic, C: Ulcer

2, other lesions Mesenteric lymph nodes, liver, spleen and bone marrow due to the activation of macrophages cause the corresponding tissues and organs to enlarge. Microscopic examination showed typhoid granuloma and focal necrosis.

Myocardial fibers may have edema or even necrosis, renal tubular epithelial cells may have edema and pale red papules (roseola) appear on the skin. Coagulation necrosis often occurs in the diaphragm, rectus abdominis and adductor muscles transsexual).

Clinically, myalgia and skin irritation occur. Most patients with typhoid fever have no obvious lesions in the gallbladder, but typhoid bacteria can multiply in bile.
Even after the patient's clinical recovery, the bacteria can still survive in the bile and be excreted from the intestine through the bile.
They are still carriers in a certain period of time, and some patients can even become chronic carriers or carriers for life.

Typhoid patients may have complications such as intestinal bleeding, intestinal perforation, and bronchial pneumonia. If there are no complications, it usually heals in 4-5 weeks. Chronic infections can also affect joints, bones, meninges and other areas.

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