Epidemiological Perspective

Cholera: The Epidemic Power of Vibrio cholerae

By Jeremy Akers, Danny Mays, Marc Siegel, MD, Visiting Focus Bloggers

Cholera patients in Haiti. Source: Rapadoo Observateur

Cholera patients in Haiti. Source: Rapadoo Observateur

This is the first in a series of posts on cholera and its impact on Haiti. The first post is a discussion of the disease itself, and serves as an examination of medical and epidemiological factors that enabled cholera to be carried by Nepalese UN peacekeepers and spread throughout Haiti with deadly force.

Haiti’s cholera epidemic began in October of 2010. Since then, researchers have been investigating the origin of the infection, as it had not been seen on the island of Hispaniola in over a century. Scientists have performed biochemical tests and genetic analysis on the bacteria in Haiti, tracing the current outbreak to a strain of Vibrio cholerae that is widespread in cholera-endemic southern Asia. The CDC found evidence that human waste from a UN peacekeeping base staffed by Nepalese officers was contaminating tributaries of the Artibonite River that flowed through many of the tent cities housing displaced Haitians after the earthquake. Journalists and the public put two and two together, and outrage has ensued, and legal action is being taken against the UN on behalf of affected Haitians.

Vibrio cholerae are microscopic bacteria that live and reproduce in water. They are resilient and can survive inclement conditions by attaching to the surface of other organisms and by forming protective biofilms. Cholera epidemics occur when the V. cholerae bacteria contaminate community water sources or food. Haiti’s inadequate infrastructure for water and sanitation, poor hygiene practice, and heavy rainfall create a conducive platform for a cholera epidemic.

Since 2010, cholera has infected over 660,000 Haitians and killed more than 8,100. The disease is not usually transmitted directly from person-to-person (like the flu). The common process of transmission–the “fecal-oral” route–is as follows: V. cholerae are excreted in the stool of an infected person and, where proper sanitation is lacking, contaminate the water supply or food. Contaminated water is ingested and many of the bacteria are killed by stomach acid. However, if enough V. cholerae are ingested, some will reach the intestines and produce toxins that cause massive intestinal secretion of water and electrolytes leading to profuse watery diarrhea and vomiting. This is the disease we call “cholera.”

Once in the intestines, V. cholerae reproduce rapidly to the point where billions can be excreted in every milliliter of diarrhea. With a daily volume of diarrhea reaching up to 20 liters, there is enormous potential to contaminate the environment. If untreated, this level of fluid loss will lead to dehydration and serious electrolyte imbalances causing muscle cramps, heart arrhythmias, kidney failure, and often death. Essentially, cholera is a disease of fluid loss through diarrhea and vomiting that leads to dehydration with potentially grave physical consequences and, in the right context, it is easy to transmit and can result in epidemics.

V. cholerae infections can be mild, mimicking Traveler’s diarrhea, or completely asymptomatic. This is one of cholera’s most powerful means to cause deadly epidemics because, even in the absence of overt symptoms, bacteria are still shed in the stool. If infected people have mild or absent symptoms, they are more likely to travel and take fewer hygiene precautions. Cholera often spreads geographically via human movement. In a globalizing world, there is unprecedented opportunity for pathogens to be introduced into vulnerable geographic regions where the local population lacks preexisting immunity. Along these lines, recent research has proven that the movement of UN troops from Nepal was almost certainly the avenue by which cholera came to Haiti.

Cholera is a somewhat ironic disease in that the source of the infection is also the basis of the treatment: a simple solution of water and electrolytes known as “ORS” (oral rehydration salts). It is essentially GatoradeTM. Antibiotics may be of some benefit in severe cases, but the most important intervention is restoration of water and electrolyte balance in the body using ORS. If an infected person is treated promptly and appropriately, the mortality rate is about 1%. If proper treatment is not provided in time, mortality can reach 60%. Given the simplicity of the treatment, management of a cholera outbreak “should” be feasible. As the death toll in Haiti continues to climb, clearly there is more to the story.

 Additional References:
  •  Saha, D. et al. Hunter’s Tropical Medicine and Emerging Infectious Diseases. Copyright © 2013, Elsevier Inc.
  •  Webber, R. Communicable Diseases: A Global Perspective. Copyright © 2012, CABI, Wallingford, UK