Shigellosis Aaqib Raneez Group 45 3rd Course • Also known as bacillary dysentery and is caused by the shigella species of bacteria, namely, S.dysentariae, S.flexnerii, S.boydii, S.sonnei. • It is a gram negative, non spore forming, • Facultative anaerobic, rod shaped bacteria. • It is an acute intestinal infection with common infection of the large intestine with necrosis of the mucosa, and symptoms of intoxication. • Source of infection – patients with acute or chronic forms of the shigella and asymptomatic carriers, and the housefly can also lead to spread. • Mode of transmission – fecal oral transmission, sometimes water borne in countries with poor hygiene, and direct contact with household items. • Most severe course is run by S.dysentariae and the others have a milder course. Microscopic Picture • Surrounding the lymphoid follicle the mucosa undergoes necrosis and the surrounding regions have inflammatory infiltrate and edema, sometimes there may be a fibrino-suppurative pseudomembrane over the follicles. Macroscopic Appearance Superficial transverse ulcerations seen in the regions of lymphoid follicles with the intact mucosa appearing blood filled, hyperemia and edematous. Local changes • It develops over 4 characteristic stages • 1) catarrhal colitis – 2/3 days and includes congestion and edema, small zones of necrosis • 2)fibrinous colitis – 5-10 days, the necrosis spreads and now there is inflammatory lymphocytic infiltration, and there is fibrinous depositions on the membrane and may affect nerve plexuses • 3)ulcerative colitis – development of ulceration and may perforate or bleed • 4)ulcerative healing – there is granulation tissue and connective tissue accumulating with the formation of a scar, large scars can impair peristalsis and have lumen stenosis. General systemic changes • May not occur very often but are likely and have changes in different parts of the body. • There is splenic hyperplasia, fatty degeneration of the liver and heart, and necrosis and dystrophy of kidney tubules. Complications • Perforation of the ulcer leading to hemorrhages, peritonitis and sepsis • Intestinal phlegmons and intestinal stenosis • Extraintestinal complications like pneumonia, pyelitis, pyelonephritis, arthritis, amyloidosis • Usually it is self limiting or require minor antibiotic course and therefore has a good prognosis however in very severe conditions it can be fatal with 600,000 deaths per annum.
