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Cholera: Causes, Treatment and Prevention

Cholera: Causes, Treatment and Prevention
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  • 0:05 King Cholera
  • 1:40 Vibrio Cholerae Background
  • 2:46 Diagnosis and Treatment
  • 4:55 Prevention
  • 6:45 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

Cholera is a deadly disease characterized by profuse, watery diarrhea. In this second lesson dedicated to cholera, we will examine the treatment and prevention of the disease.

King Cholera

The disease cholera has been ravaging human populations for many hundreds of years. In fact, since 1817, there have been seven major cholera pandemics. A pandemic is a high number of cases of a disease that occur at about the same time worldwide.

You are probably thinking that it is a good thing you live in a time when huge disease outbreaks don't occur very often, especially in the United States. I bet you don't even know anyone that has ever had cholera, so the last great cholera pandemic must have occurred a long time ago, right? Well, actually no. The seventh, and latest, major pandemic began in 1961 and is still occurring to this day.

But, how can this be possible? Let's take a look at the data. In 1961, a new strain of Vibrio cholerae, which is the bacteria that causes cholera, emerged. Since this emergence in 1961, five million cases of cholera have been reported. Of these, 250,000 people have died. In 2009, 220,000 people developed cholera and nearly 5,000 died of the disease.

So, why don't most people know about this pandemic? Why is the United States not issuing warnings? The answer lies on this map:

Map showing countries with the highest incidences of cholera
map showing location of most cholera

The areas in red account for nearly all cases of cholera. The United States averages less than 25 cases a year. Cholera may not be an imminent threat to your health, but billions of people worldwide deal with the specter of king cholera every day.

Vibrio Cholerae Background

Vibrio cholerae is a motile, Gram-negative, curved, rod-shaped bacteria that causes the disease cholera. The bacteria can be found as free-living cells in coastal and brackish waters. It can also survive in the human intestine, making it a common contaminant in sewage. Most people catch cholera by drinking water contaminated by human feces.

For most people, drinking a few hundred thousand V. cholerae cells will produce only a very mild diarrhea, if any symptoms at all. In a very unlucky five percent of infected people, the bacteria will cause a severe case of cholera. The bacteria release an exotoxin into the small intestine that causes a massive flow of water and electrolytes like sodium, chloride and bicarbonate, into the intestine. What results is a very severe and profuse case of diarrhea.

A patient can lose up to one liter of fluid every hour. Dehydration occurs very rapidly and, if left untreated, 60% of the people that develop these severe symptoms will die as a result of rapid dehydration.

Diagnosis and Treatment

It is not uncommon for people to begin having diarrhea in the morning and die from dehydration in the evening. As a result, a prompt diagnosis is crucial. Fortunately, the appearance of the diarrhea can be a great diagnostic tool. Rice water stools is the name given to cholera diarrhea due to its colorless, watery appearance, flecked with rice-like mucus. Having diarrhea like this means you most likely have cholera.

To confirm the diagnosis, technicians will microscopically examine feces, looking for the characteristic curved, rod-shaped appearance of V. cholerae cells. If these cells are present, a doctor might try and grow the bacteria to identify the exact strain. Culturing can take several days, so treatment often starts as soon as the diarrhea begins, even before the microscopic examination.

The reason treatment can begin without a diagnosis is because the first line of treatment is simply to counteract the worsening dehydration. The patient is given large amounts of fluid and electrolyte supplements to try and get ahead of the fluid loss. As long as the patient is able to swallow, the fluids and supplements are given orally. This route doesn't require any special equipment or expertise, and it doesn't puncture the skin, risking additional infections like intravenous fluids would.

In addition to fluid therapy, antibiotics can be used to shorten the duration of symptoms and reduce the total amount of fluid loss. Antibiotic resistant strains of V. cholerae seem to pop up nearly as fast as new drugs are found to combat them. Currently, adults are given doxycycline, and children are given azithromycin.

Recent studies have also shown that zinc supplements can further reduce the duration and severity of symptoms in children. The zinc seems to reduce the water and ion loss by influencing the intestinal cells directly, but the exact mechanism is still unclear. Zinc has not been shown to be effective in adults, though. The combination of fluids, electrolytes and antibiotics can reduce the death rate from cholera from around 60% to about one percent.

Prevention

It looks like we have it pretty good living in the United States. Cases are rare, only a low percentage of people actually even get severe cholera, and we have great hospitals. So, you might think there is no real reason to worry about catching the disease. You might be right, but do you live near the Gulf Coast, like to travel overseas or enjoy eating shellfish? If the answer to any of these is yes, don't stop paying attention quite yet.

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