10/08/2011

Cholera


Vibrio cholera bacteria in SEM micrograph

What is 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 developdehydration 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.
In cholera bacteria, the "rugose" variant
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 isPasteurella 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.


What causes cholera, and how is cholera transmitted?

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. choleraeserotypes 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 incontaminated food, especially seafood such as raw oysters.

What is the history of cholera?

Cholera has likely been with humans for many centuries. Reports of cholera-like disease have been found in India as early as 1000 AD. Cholera is a term derived from Greek khole (illness from bile) and later in the 14th century tocolere (French) and choler (English). In the 17th century, cholera was a term used to describe a severe gastrointestinal disorder involving diarrhea and vomiting. There were many outbreaks of cholera, and by the 16th century, some were being noted in history. England had several in the 18th century, most notable being in 1854, when Dr. John Snow did a classic study in London that showed a main source of the disease (resulting in about 500 deaths in 10 days) came from at least one of the major water sources for London residents termed the "Broad Street pump." The pump handle was removed, and the cholera deaths slowed and stopped. The pump is still present as a landmark in London. Although Dr. Snow did not discover the cause of cholera, he did show how the disease could be spread and how to stop a local outbreak. This was the beginning of modern epidemiologic studies.
V. cholerae was first isolated as the cause of cholera by Filippo Pacini in 1854, but his discovery was not widely known until Robert Koch (who also discovered the cause of tuberculosis), working independently 30 years later, publicized the knowledge and the means of fighting the disease. The history of cholera repeats itself. The U.S. National Library of Medicine houses original documents about multiple cholera outbreaks in the U.S. from the 1820s to the 1900s, with the last large outbreak in 1910-1911. Since the 1800s, there have been seven cholera pandemics (worldwide outbreaks).
Multiple outbreaks worldwide continue into the 21st century with outbreaks in India, Iran, Vietnam, and several African countries in the last 10 years (most recent outbreaks occurred in Haiti and Nigeria in 2010-2011). Why is cholera history repeating itself? The answer can be traced back to Dr. Snow's studies that show a source (water or occasionally food) contaminated with V. cholerae can easily and rapidly transmit the cholera-causing bacteria to many people. Until safe water and food is available to all humans, it is likely cholera outbreaks will continue to happen
 Symptoms 

  • Abdominal cramps
  • Dry mucus membranes or mouth
  • Dry skin
  • Excessive thirst
  • Glassy or sunken eyes
  • Lack of tears
  • Lethargy
  • Low urine output
  • Nausea
  • Rapid dehydration
  • Rapid pulse (heart rate)
  • Sunken "soft spots" (fontanelles) in infants
  • Unusual sleepiness or tiredness
  • Vomiting
  • Watery diarrhea that starts suddenly and has a "fishy" odor
Exams and Tests 

Tests that may be done include:
  • Blood culture
  • Stool culture

How is cholera diagnosed?

Preliminary diagnosis is usually done by a caregiver who takes a history from the patient and observes the characteristic rice-water diarrhea, especially if a local outbreak of cholera has been identified. The diarrhea fluid is often teeming with motile, comma-shaped bacteria (presumptively V. cholerae). The definitive diagnosis is made by isolation of the bacteria from diarrhea fluid on a selective medium thiosulfate-citrate-bile salts agar (TCBS). Reagents for serogroupingVibrio cholerae isolates are available in all state health department laboratories in the U.S. Readers may see terms like serotypes Inaba, Ogawa, and Hikojima to describe V. cholerae; they simply indicate which O antigens (O antigens designated A, B, or C) are found on these strains of V. cholerae.PCR tests have also been developed to detect cholera but currently they are not as widely used as other tests based on type-specific antiserum.
Definitive diagnosis helps to distinguish cholera from other diseases caused by other bacterial, protozoal, or viral pathogens that cause dysentery (gastrointestinal inflammation with diarrhea)
Teatment 

The objective of treatment is to replace fluid and electrolytes lost through diarrhea. Depending on your condition, you may be given fluids by mouth or through a vein (intravenous). Antibiotics may shorten the time you feel ill.
The World Health Organization (WHO) has developed an oral rehydration solution that is cheaper and easier to use than the typical intravenous fluid. This solution of sugar and electrolytes is now being used internationally.
Possible Complications 

  • Severe dehydration
  • Death
When to Contact a Medical Professional 

Call your health care provider if :
  • You develop severe watery diarrhea
  • You have signs of dehydration, including:
    • Dry mouth
    • Dry skin
    • "Glassy" eyes
    • Lethargy
    • No tears
    • Rapid pulse
    • Reduced or no urine
    • Sunken eyes
    • Thirst
    • Unusual sleepiness or tiredness 

 Prevention
The U.S. Centers for Disease Control and Prevention does not recommend cholera vaccines for most travelers. (Such a vaccine is not available in the United States.)
Travelers should always take precautions with food and drinking water, even if vaccinated.
When outbreaks of cholera occur, efforts should be directed toward establishing clean water, food, and sanitation, because vaccination is not very effective in managing outbreaks.
Alternative Names 
V. cholerae; Vibrio

 
 
 

 

 
 

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