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Cholera

Cholera

Cholera is an acute infectious disease caused by a bacterium, Vibrio cholerae (V. cholerae), which results in a painless, watery diarrhea in humans. Some affected individuals have copious amounts of diarrhea and develop dehydration so severe it can lead to death. Most people who get the disease ingest the organisms through food or water sources contaminated with V. cholerae.

 

Although symptoms may be mild, approximately 5%-10% of previously healthy people will develop a copious diarrhea within about one to five days after ingesting the bacteria. Severe disease requires prompt medical care. Hydration (usually by IV for the very ill) of the patient is the key to surviving the disease.

 

The term cholera has a long history (see history section below) and has been assigned to several other diseases. For example, fowl or chicken cholera is a disease that can rapidly kill chickens and other avian species rapidly with a major symptom of diarrhea. However, the disease-causing agent in fowl is Pasteurella multocida, a gram-negative bacterium.

 

Similarly, pig cholera (also termed hog or swine cholera) can cause rapid death (in about 15 days) in pigs with symptoms of fever, skin lesions, and seizures. This disease is caused by a pestivirus termed CSFV (classical swine fever virus). Neither one of these animal diseases are related to human cholera, but the terminology can be confusing.

Symptoms

The symptoms and signs of cholera are a watery diarrhea that often contains flecks of whitish material (mucus and some epithelial cells) that are about the size of pieces of rice. The diarrhea is termed "rice-water stool" and smells "fishy". 

 

The volume of diarrhea can be enormous; high levels of diarrheal fluid such as 250 cc per kg or about 10 to 18 liters over 24 hours for a 70 kg adult can occur.

 

People may go on to develop one or more of the following symptoms and signs:

  • vomiting,
  • rapid heart rate,
  • loss of skin elasticity (washer woman hands sign),
  • dry mucous membranes,
  • low blood pressure,
  • thirst,
  • muscle cramps,
  • restlessness or irritability (especially in children).

 

People require immediate hydration to prevent these symptoms from continuing because these signs and symptoms indicate that the person is becoming or is dehydrated and may go on to develop severe cholera.

 

People with severe cholera (about 5%-10% of previously healthy people; higher if a population is compromised by poor nutrition or has a high percentage of very young or elderly people) can develop severe dehydration, leading to acute renal failure, severe electrolyte imbalances (especially potassium an sodium), and coma.

 

If untreated, this severe dehydration can rapidly lead to shock and death. Severe dehydration can often occur four to eight hours after the first liquid stool with death in about 18 hours to a few days in undertreated or untreated people. In epidemic outbreaks in underdeveloped countries where little or no treatment is available, the mortality (death) rate can be as high as 50%-60%.

Causes

Cholera is caused by the bacterium V. cholerae. This bacterium is Gram stain-negative and has a flagellum (a long, tapering, projecting part) for motility and pili (hairlike structures) used to attach to tissue. Although there are many V. cholerae serotypes that can produce cholera symptoms, the O groups O1 and O139, which also produce a toxin, cause the most severe symptoms of cholera. O groups consist of different lipopolysaccharides-protein structures on the surface of bacteria that are distinguished by immunological techniques.

 

The toxin produced by these V. cholerae serotypes is an enterotoxin composed of two subunits, A and B; the genetic information for the synthesis of these subunits is encoded on plasmids (genetic elements not in the bacterial chromosome). In addition, another plasmid type encodes for a pilus (a hollow hairlike structure that can augment bacterial attachment to human cells and facilitate the movement of toxin from V. cholerae into human cells).

 

The enterotoxin causes human cells to extract water and electrolytes from the body (mainly the upper gastrointestinal tract) and pump it into the intestinal lumen where the fluid and electrolytes are excreted as diarrheal fluid. The enterotoxin is similar to toxin formed by bacteria that cause diphtheria in that both bacterial types secret the toxins into their surrounding environment where the toxin then enters the human cells.

 

The bacteria are usually transmitted by people drinking contaminated water, but the bacteria can also be obtained in contaminated food, especially seafood such as raw oysters.

Treatment

The CDC (and almost every medical agency) recommends rehydration with ORS (oral rehydration salts) fluids as the primary treatment for cholera. ORS fluids are available in prepackaged containers, commercially available worldwide, and contain glucose and electrolytes.

 

The CDC follows the guidelines developed by the WHO (World Health Organization) and are as follows:

WHO Fluid Replacement or Treatment Recommendations (as per the CDC)

Patient condition  

Treatment  

Treatment volume guidelines; age and weight

No dehydration  

Oral rehydration salts (ORS)  

Children < 2 years: 50 mL-100 mL, up to 500 mL/day
Children 2-9 years: 100 mL-200 mL, up to 1,000 mL/day
Patients > 9 years: As much as wanted, to 2,000 mL/day

Some dehydration  

Oral rehydration salts (amount in first four hours)  

Infants < 4 mos (< 5 kg): 200-400 mL
Infants 4 mos-11 mos (5 kg-7.9 kg): 400-600 mL
Children 1 yr-2 yrs (8 kg-10.9 kg): 600-800 mL
Children 2 yrs-4 yrs (11 kg-15.9 kg): 800-1,200 mL
Children 5 yrs-14 yrs (16 kg-29.9 kg): 1,200-2,200 mL
Patients > 14 yrs (30 kg or more): 2,200-4,000 mL

Severe dehydration  

IV drips of Ringer Lactate or, if not available, normal saline and oral rehydration salts as outlined above 

 

Age < 12 months: 30 mL/kg within one hour*, then 70 mL/kg over five hours
Age > 1 year: 30 mL/kg within 30 min*, then 70 mL/kg over two and a half hours

*Repeat once if radial pulse is still very weak or not detectable

  • Reassess the patient every one to two hours and continue hydrating. If hydration is not improving, give the IV drip more rapidly. 200mL/kg or more may be needed during the first 24 hours of treatment.
  • After six hours (infants) or three hours (older patients), perform a full reassessment. Switch to ORS solution if hydration is improved and the patient can drink.

 

In general, antibiotics are reserved for more severe cholera infections; they function to reduce fluid rehydration volumes and may speed recovery.

 

Although good microbiological principals dictate it is best to treat a patient with antibiotics that are known to be effective against the infecting bacteria, this may take too long a time to accomplish during an initial outbreak (but it still should be attempted); meanwhile, severe infections have been effectively treated with tetracycline (Sumycin), doxycycline (Vibramycin, Oracea, Adoxa, Atridox and others), furazolidone (Furoxone), erythromycin (E-Mycin, Eryc, Ery-Tab, PCE, Pediazole, Ilosone), or ciprofloxacin (Cipro, Cipro XR, Proquin XR) in conjunction with IV hydration.

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