What is Typhoid Fever
The disease Typhoid Fever is caused by S.typhi, S.paratyphi A, B and C. The infection occurs through the orofaecal route. Some of the organisms pass the acidic barrier of the stomach and enter the intestinal lumen. In the intestine, the organisms first attach to the epithelial cell and then, by pinocytic movement, enter the intracellular space.
The organisms may multiply in the pinocytic vacuole & then pass to lamina propria from the other end of the epithelial cell. In the lamina propria, the organisms enter the lacteals (small lymphatics) and through them to local lymph glands and the thoracic duct. This duct opens into the bloodstream and thus the organisms enter into the bloodstream. This is the stage of a primary bacteremia. The organisms are then carried to different reticuloendothelial organs by the bloodstream like liver, spleen, bone marrow, kidney, lymph nodes and Payer‘s Patches of the small intestine.
The organisms multiply in these organs and after sufficient multiplication, they enter the bloodstream a second time. This is the stage of secondary bacteremia and is the time that patients develop a fever. The swelling of Payer‘s Patches causes ulceration of the small intestine. Intestinal perforation is also sometimes noticed in cases of enteric fever. The perforation is due to antigen-antibody hypersensitivity. The micro-organisms multiply in intestinal lymphoid tissues and are excreted in stools.For the isolation of organisms different cultures at different times of the disease are useful:
A blood culture is positive in the 1st week.
A urine culture is positive in the 3rd and 4th weeks of the illness.
A stool culture is positive in the 2nd to 4th weeks of illness.
The serological test to monitor the disease is the Widal Test which becomes positive after a week of the illness. The titer rises after 7-10 days. Demonstration of a rising titer helps in diagnosis. Typhidot (an immuno-chromatographic technique) is another test on the serum that detects both IgG and IgM antibodies against a 60kilo dalton protein in the cell wall of Salmonella Typhi. It is sensitive but more expensive. There are other serological tests, but they are not commonly available.
