Cholera is an acute, water-borne, bacterial infection of the intestine. The worst symptoms, which may be mild, severe, or fatal, are profuse diarrhea, vomiting, and cramps. The disease is widespread with reports of millions of cases annually and in some years more than 100,000 deaths.
Definition & Facts
Cholera, in severe cases, can be fatal within hours if untreated. Oral rehydration therapy using salts is effective and successful in as many as 80 percent of cases. Safe drinking water and regular sanitation are essential for control of cholera. Oral cholera vaccines are effective at preventing cholera.
Symptoms & Complaints
Most cases cause mild or moderate diarrhea often difficult to distinguish from that caused by other agents. About one infected individual in ten develops the signs and symptoms typical of cholera, usually within a few days of exposure:
- Diarrhea. Diarrhea from cholera has a sudden onset that quickly may cause dangerous loss of bodily fluid, as much as a liter per hour. Diarrhea from cholera often has a pale appearance that resembles water which has rinsed rice.
- Nausea and vomiting. Especially in the early stages of the infection, vomiting may be violent and painful and last for hours at a time.
- Dehydration. Mild to severe dehydration with loss of 10 percent or more of body weight can occur within hours after the onset of initial symptoms manifested by irritability, lethargy, dry mouth, extreme thirst, shriveled skin, little or no urination, low blood pressure, and a coronary arrhythmia or bradychardia. Dehydration may lead to an electrolyte imbalance, which brings on muscle cramps and rapid loss of sodium and potassium salts.
- Shock. One of the most serious complications of dehydration, shock occurs when low blood volume causes low blood pressure and a low amount of oxygen in the body. If untreated, severe shock can kill the patient in minutes.
The cholera bacterium is Vibrio cholerae, a species not endemic to humans nor is its presence in human digestive systems part of its natural life cycle, which shifts between various snails, crustaceans, and free-floating and static planktonic forms resident in the silt and muck of estuarial environments. Entry into the human ecosystem is most commonly through contaminated food or water. When humans consume shellfish from estuaries and fail to cook them thoroughly, they can swallow enough of the bacteria to cause a case of cholera. Poorly cleaned vegetables irrigated by contaminated water are other common sources.
In situations of substandard sanitation as in refugee camps or areas with limited or stagnant water resources, a single infected victim can contaminate the water supply for an entire population. The Vibrio cholerae binds to human intestinal walls and interferes with the normal flow of sodium chloride. A soluble toxin released by the bacteria activates the mucous membrane of the intestinal wall to secrete so much isotonic fluid that profuse, watery diarrhea, extreme loss of fluid and electrolytes, and dehydration and collapse follow quickly. Cholera seldom passes from person to person through casual interpersonal contacts.
Diagnosis & Tests
The culture method is the most recommended test for diagnosis of cholera. The method places a patient's stool samples on on a plate of thiosulfate-citrate-bile salts-sucrose agar, a medium that separates the bacteria from the rest of the diarrheic output. On incubation, the bacteria appear as yellow clumps which are then analyzed to detect the exact strain of cholera. This definitive diagnosis distinguishes cholera from protozoal, viral, or other bacterial causes of dysentery.
In areas where cholera is endemic, rapid immunochromatographic analysts place dipstick strips into stool samples and read the lines displayed. The appearance of two red lines on the dipstick confirms cholera; the appearance of only one eliminates it. This test takes up to 15 minutes to produce results for a diagnosis. Blood testing for Vibrio cholerae antibodies also can confirm a cholera diagnosis. Although there are over 100 Vibrio cholerae serogroups according to cell surface antigens, only two, serogroups O1 and O139, are causative.
Treatment & Therapy
Oral rehydration, highly effective, safe, and simple to administer, is the principal treatment for cholera. Rice-based are preferable to glucose-based solutions for efficiency. In cases of severe dehydration, intravenous therapy as well as oral rehydration may be necessary. Large fluid volumes and continuous fluid replacement until diarrhea subsides may be necessary. Ten percent of the patient's body weight in fluid may be needed in the first few hours. If acidosis is present, the potassium level may appear to be normal, but, as the rehydration proceeds, the level may fall rapidly and require replacement, which may be by foods high in potassium content.
One to three days of antibiotic treatment shortens the course of the disease, ameliorates the severity of the symptoms, and reduces fluid requirements. Recovery without antibiotics will be complete, however, with sufficient rehydration. The World Health Organization recommends antibiotics only for severe cases.
Prevention & Prophylaxis
Identification, treatment, and isolation of cholera cases prevent further transmission of the disease. Public education campaigns can help contain the bacterium and prevent its spread among the population. The Centers for Disease Control reports that two oral vaccines licensed in areas where cholera is endemic have reduced the likelihood of infection of area residents by more than 50 percent over two years. The World Health Organization recommends vaccination of high-risk children, the elderly, and HIV patients in countries with high cholera rates.