Shigella Pathogensis PDF

# Bacillary Dysentery (Shigellosis) Bacillary Dysentery is an inflammatory colitis caused by the Shigella group of organisms. - The Shigella group of organisms are gram-negative, non-spore forming bacilli. - They primarily affect the large bowel. - There are four serological subgroups: - *Sh....

# Bacillary Dysentery (Shigellosis) Bacillary Dysentery is an inflammatory colitis caused by the Shigella group of organisms. - The Shigella group of organisms are gram-negative, non-spore forming bacilli. - They primarily affect the large bowel. - There are four serological subgroups: - *Sh. dysentriae* has 10 types and the most severe infection is caused by type 1 (*Sh. Shiga*). - *Sh. Flexenireri* has 6 serotypes. - *Sh. boydii* has 15 serotypes. - *Sh. sonei* has 1 type. ## Epidemiology - 140 million cases of Shigellosis and almost 600,000 deaths occur annually. - Poor sanitation and overcrowding facilitate transmission and infection can be sporadic or an outbreak. - The mortality rate in epidemics is 2-6%. - Transmission takes place by the fecal-oral route and Shigella is highly host-dependent to humans. - The source of infection is infected cases, convalescent carriers, and chronic cases. ## Pathogenesis - Depends on the type of cytotoxins - Neurotoxin causes convulsions and peripheral neuropathy. - Enterotoxin causes secretory diarrhea. - Cytotoxin causes destruction of the epithelial cells (villi), ulcers, and microabscess, leading to exudative inflammation, fibrosis, and chronic dysentery or colitis. - Bacteremia is rare. ## Clinical Features - Depends on the type of organism and the severity of infection. - The incubation period is 1-5 days. - Onset is abrupt with a fever that can reach up to 40-41°C. - Diarrhea is initially watery due to the effect of enterotoxins in the small bowel. - After a few days, the patients develop the classical symptoms of dysentery. - Passage of small volume stool about 10-30 times/day consisting mainly of blood, mucus, and pus (*red current jelly stool*) associated with abdominal cramps and tenesmus (*painful straining with stooling that may lead to rectal prolapse*). ## Complications - Perforation - Peritonitis - Hemorrhage - Severe dehydration that can lead to shock and acute renal failure - Sepsis - Convulsions - Portal pyemia leading to liver abscess - Stricture of the large bowel - Hemorrhoids and rectal prolapse in children. ## Hemolytic Uremic Syndrome - Seen with type 1 *S. dysentriae* that produces high levels of Shigella toxins. - Seen at the end of the first week of Shigellosis. - Hemolysis leads to oliguria and a marked drop in hematocrit, causing anuria and acute renal failure. - Severe anemia that can lead to congestive heart failure. - Leukomoid reaction with a white blood cell count greater than 50,000. - Thrombocytopenia, hyponatremia, and hypoglycemia. - 5-10% die of acute renal failure and 50% of survivors will develop chronic renal failure. ## Reiter Disease - Irritation of the eyes, urethra, and conjunctiva, and arthritis. ## Diagnosis - Stool macroscopy reveals mucous, pus, and blood, and it's not offensive and is alkaline in a test that is usually acidic. - Stool microscopy shows 90% pus cells with numerous red blood cells and macrophages containing red blood cells. - Stool culture ## Differential Diagnosis of Acute Bacillary Dysentery - Acute amoebic dysentery: Patient is usually not febrile, onset is insidious, and the patient is mobile and seeks medical advice (*walking dysentery*). The stool is large, offensive and acidic, and shows few pus cells and trophozoites. - Food poisoning. - Campylobacter jejuni and toxigenic *E. coli*. - Dysenteric malaria. ## Differential Diagnosis of Chronic Bacillary Dysentery - Intestinal schistosomiasis - Ulcerative colitis - Crohn's Disease - Intestinal tuberculosis - Carcinoma of the colon ## Treatment - Replace fluids. - Symptomatic treatment. - Measure electrolytes in severe cases and if the bicarbonate is low and the patient is acidotic, give intravenous bicarbonate. - Antibiotics: - Resistance to antibiotics like tetracycline, chloramphenicol, trimethoprim, and sulfamethoxazole is almost universal. - The most recommended drug is Nalidixic Acid (*50 mg/kg body weight*) 500 mg every 6 hours for 5 days, but resistance is increasing. - Second-generation 4 quinolones like Norfloxacin 400 mg twice a day for 5 days. - Third-generation Ciprofloxacin 500 mg twice a day for 5 days. These are highly effective. - The role of antidiarrheal agents is controversial. - Atropine sulfate - Diphenoxylate (Lomotil) - Loperamide (Imodium) - They may decrease diarrhea but enhance the severity of the disease by delaying excretion of the organism.