Cholera

 

a. Clinical Syndrome.

(1) Characteristics. Cholera is a diarrheal disease caused by Vibrio cholera, a short, curved, gram-negative bacillus. Humans acquire the disease by consuming water or food contaminated with the organism. The organism multiplies in the small intestine and secretes an enterotoxin that causes a secretory diarrhea. When employed as a BW agent, cholera will most likely be used to contaminate water supplies. It is unlikely to be used in aerosol form.

(2) Clinical Features. Cholera may present as mild diarrhea or as a fulminant disease characterized by profuse watery diarrhea with fluid losses exceeding 5 to 10 liters or more per day. Without treatment, death may result from severe dehydration, hypovolemia and shock. Vomiting is often present early in the illness and may complicate oral replacement of fluid losses. There is little or no fever or abdominal pain.

b. Diagnosis.

(1) Routine Laboratory Findings. On microscopic examination of stool samples there are few or no red cells or white cells. Serum electrolytes may demonstrate hypokalemia or if inappropriate fluid replacement has been given, may show hypernatremia or hyponatremia. Acidosis and renal failure may accompany severe dehydration.

(2) Differential Diagnosis. Watery diarrhea can also be caused by enterotoxigenic E. coli, rotavirus or other viruses, noncholera vibrios, or food poisoning due to ingestion of preformed toxins such as those of Clostridium perfringens, Bacillus cereus, or Staphylococcus aureus.

(3) Specific Laboratory Diagnosis. Vibrios can be identified in stool by darkfield or phase contrast microscopy, and Vibrio cholera can be grown on a variety of culture media. Bacteriologic diagnosis is not necessary to treat cholera or related watery diarrheas.

c. Therapy. Treatment of cholera depends primarily on replacement of fluid and electrolyte losses. This is best accomplished using oral dehydration therapy with the World Health Organization solution (3.5 g NaCL, 2.5 g NaHC03, 1.5 g KC1 and 20 g glucose per liter). Intravenous fluid replacement is occasionally needed when vomiting is severe, when the volume of stool output exceeds 7 liters/day, or when severe dehydration with shock has developed. Antibiotics will shorten the duration of diarrhea and thereby reduce fluid losses. Tetracycline (250 mg every 6 hr for 3-5 days) or doxycycline (200 mg initially followed by 100 mg every 12 hr for 3-5 days) is generally adequate. Other effective drugs include ampicillin (250 mg every 6 hr for 5 days) and trimethoprim sulfamethoxazole (one tablet every 12 hr for 3-5 days).

d. Prophylaxis. Improved oral cholera vaccines are presently being tested. Vaccination with the currently available killed suspension of V. cholera provides about 50% protection that lasts for no more than 6 months. The initial dose is two injections given at least 1 week apart with booster doses every 6 months.

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