Cholera, entrenched in Haiti, starts to spread
Haiti, the nation that cannot get a break, has become the epicenter of a Caribbean cholera epidemic. Nine months after an estimated 200,000 died in the Jan. 12, 2010 earthquake, watery diarrhea — a characteristic of cholera — began to beset Haitians.
The toxins from the bacterium Vibrio cholerae upset the chemistry of the intestinal tract, causing diarrhea, dehydration and sometimes death.
As of Oct. 17, 2013, the Caribbean epidemic has sickened 684,085 people and killed 8,361, according to the Centers for Disease Control. Annually, worldwide, cholera kills about 100,000 and infects three to five million.
Cholera has now spread to Dominican Republic (31,090 cases and 458 deaths), Cuba (678 cases) and Mexico (176 cases between 9 Sept. and 25 Oct. 2013).
Cholera is spread via feces, and the disease could spread when infected people travel to areas with poor sanitation. It’s also possible that aquatic animals harboring Vibrio cholerae have drifted across the sea. However, other affected countries are more developed and/or more organized than Haiti, so those epidemics may ebb before Haiti’s latest tragedy ceases.
A clean, just and prosperous world would have no cholera, as the bacterium is spread from feces into food or drinking water. As cholera continues to ravage Haiti, what do we know about the bacterium and the disease?
Vibrio cholerae: Aquatic attacker
First off, the pathogen is extremely common. “Vibrio cholerae is part of the natural flora of aquatic systems: coasts, estuaries, rivers, ponds and lakes,” says Rita Colwell, professor emerita at the University of Maryland, who has studied the organism and its disease for 40 years. The bacterium lives with crustaceans called copepods and with drifting animals called zooplankton in relationships that likely provide benefits to both sides.
According to the standard explanation, V. cholerae reached Haiti in a United Nations peacekeeper who arrived after the earthquake carrying the pathogen but without active cholera. But Colwell is not convinced. The genetics of the strains in Haiti “are not absolutely identical to the Nepal strain. They are related, but are also related to strains from Zambia, Asia and Mexico,” she says.
Colwell is also skeptical about the assumption that this is Haiti’s first cholera epidemic. Although there are no records of positive lab tests, historically, “Cases of extreme watery diarrhea have been admitted to hospitals in Haiti,” she notes. “In addition, cases of cholera have been reported [elsewhere] in the West Indies.”
The mere presence of V. cholerae is not enough to spark an epidemic; conditions must be right, says J. Glenn Morris, a professor of infectious disease at the University of Florida. “The microorganism can quite happily live in the environment of Haiti, but to cause cholera disease, it’s got to get from the river into somebody’s intestinal tract.”
Cholera and myriad other gastrointestinal blights are blocked by basic infrastructure that people in wealthy countries take for granted, says Morris, director of the Emerging Pathogens Institute at Florida. “If you have a good water system, you are not going to ingest it. But if the water system does not work, because it was destroyed by an earthquake, or was not good to start with, and you are getting drinking water from the river, and people are washing clothes and dishes in the river, and people who are sick don’t have a latrine and are defecating into the river, you significantly increase the chance of getting it into your own gut, and starting the epidemic cycle.”
The persistent plague
One key to coping with cholera is understanding how V. cholerae survives for years in its watery environment. Morris notes that “rivers often lack the nutrients for happy bacteria to chew on,” and says the answer lies in Vibrio cholera’s flexibility and “ability to turn on different sets of genes as needed.”
To test whether the microbe could stay alive for long periods, Morris and colleagues grew Vibrio cholerae in containers of low-nutrient lake water and “found they could survive for years, literally. When we looked 700 days later, they were still alive. Under the electron microscope, they had shrunk down, looked different from the normal fat, juicy Vibrio cholera.”
When this so-called “persister form” was dropped into a richer environment, “It immediately flipped back to its normal self, ready to go and do its thing,” Morris says1.
Other bacteria change into durable forms for extended survival, “and it appears that cholera can do the same thing,” Morris says, clarifying that the persister is not a spore — a tiny capsule formed by stressed-out bacteria. “A spore can persist in dry conditions for extended periods. This is a live, culturable organism that needs to stay in a water environment.”
Vaccine: A realistic solution?
The obvious way to deal with cholera is with effective sewage treatment and supplies of clean, safe water — measures that have the fringe benefit of preventing many other intestinal diseases. But that’s easier said than done in Haiti, which ranks #161 of 186 nations on the United Nations’ Human Development Index, and is still struggling to recover from the catastrophic 2010 earthquake.
Oral rehydration therapy is a last-ditch, lifesaving treatment for cholera. These low-cost packages of salt and sugar restore a healthy chemical balance to the intestines, slowing or stopping the incessant, deadly diarrhea.
Antibiotics can also work, if the bacteria are susceptible, as they are so far in Haiti.
What about cholera vaccine? Morris notes that a study in Bangladesh2 found that vaccine was effective enough — in terms of cost and impact — to be worthwhile in Haiti. Although cholera vaccine is only about 60 percent effective, the resulting “herd immunity” would greatly reduce the total toll.
But Morris sees little enthusiasm for cholera vaccine among the big drug companies. “Big pharma has decided that cholera vaccine does not make sense. People with cholera are poor, and so they are not going to make any money.”
For some time, Morris says, “no one in the world was producing cholera vaccine.” A vaccine made by an Indian company has been field-tested in Haiti and Bangladesh, but “We don’t know how well it worked, we have not had a chance to monitor the vaccinated population.”
A vaccine could “play a critical role” in Haiti, where there is concern that the organism may become permanently established, “and public health is lousy,” Morris says.
The World Health Organization suggests that “Cholera vaccination should be used in conjunction with other interventions. Vaccination provides an immediate short-term response while the longer term interventions such as improving water and sanitation are put into place.” WHO does not suggest blanket immunization in cholera zones.
An environmental illness
If cholera is found in the environment, it also responds to environmental cues. In a study3 of records from inland areas in India and Pakistan, Colwell says, “We looked at air temperature and deaths from cholera and found that the correlation was quite dramatic. When the preceding two months had higher temperatures, and much higher rainfall, coupled with a population event, like a religious festival, this combination results in a major epidemic.”
High temperatures could accelerate the growth of the cholera bacterium, and heavy rainfall can overwhelm or obliterate sanitary infrastructure, loosing cholera on the population. In 2010, Haiti’s air temperature was significantly above average, says Colwell, and in the fall, Hurricane Tomas unleashed 10 centimeters of rainfall on Nov. 5, 2010 alone, just before the cholera epidemic began. Although warmer temperatures accord with the global warming trend, the connection between warming and hurricane numbers and intensity is debated.
Beyond disrupting life and creating a nightmare for refugees, the earthquake may have fed the cholera epidemic by causing a giant grinding motion in bedrock, releasing ground-up limestone that raised river pH to 8.6. “This is the alkalinity we use to enrich for Vibrio cholerae in the laboratory,” Colwell says.
“In 2010, we had a severe earthquake, the rivers are affected, the pH is elevated, the summer is the hottest in 60 years,” says Colwell, “and in October-November, Hurricane Tomas skirts the island, with the highest rainfall in 60 years. With the infrastructure being very poor and then badly damaged, it was the perfect storm.”
But what good is understanding weather that conduces to cholera, if it’s impossible to change the weather? Because forecasting an epidemic could be extremely useful, Colwell says. When cholera threatens, local authorities can promote hand washing and water cleanliness. They can distribute vaccines and stock oral rehydration packets before the watery diarrhea starts and the dying begins.
Overall, Colwell thinks the cholera-in-Haiti picture is more complex than the conventional story: “peacekeeper arrives with asymptomatic infection, and thousands die as an old killer sweeps through a nation ravaged by poverty, corruption and earthquake.”
“You cannot rule out that the bacterium may have been imported,” she says, but it’s also possible that environmental conditions unleashed a resident pathogen. “I think what we are observing is a much more complicated situation. It’s tragic. It was a huge epidemic, but when you put together the conditions of sanitation, weather, the earthquake and the refugee camps, we feel you could have predicted there would be a cholera epidemic.”
– David J. Tenenbaum
Terry Devitt, editor; S.V. Medaris, designer/illustrator; Yilang Peng, project assistant; David J. Tenenbaum, feature writer; Amy Toburen, content development executive
- Survival of Vibrio cholerae in Nutrient-Poor Environments Is Associated with a Novel “Persister” Phenotype, Mohamma Jubair et al, PLOS ONE, Sep 18, 2012DOI: 10.1371/journal.pone.004518 ↩
- Khan IA, et al. Coverage and cost of a large oral cholera vaccination program … Vaccine (2013), http://dx.doi.org/10.1016/j.vaccine.2013.10.021 ↩
- Environmental Factors Influencing Epidemic Cholera, Antarpreet Jutla, et al, Am. J. Trop. Med. Hyg., 89(3), 2013, pp. 597–607 ↩
- A Lion in Our Village — The Unconscionable Tragedy of Cholera in Africa ↩
- 5 Tech Breakthroughs Bringing Clean Water to the Developing World ↩
- Why Is Cholera Spreading in Haiti Now? ↩
- Water-related Diseases: Hepatitis, Cholera, Malaria and So On ↩
- Climate’s Strong Fingerprint in Global Cholera Outbreaks ↩