Cholera in Haiti

Haiti is having a bad year.

Nine months after the earthquake it has been estimated that 1 million people are still living in tents, and now there’s a cholera outbreak to deal with. These two facts are not unrelated— to quote the Pan American Health Organization:

Natural and man-made disasters which produce overcrowding, a scarcity of safe drinking water, improper elimination of human waste, and the contamination of food during or after its preparation are risk factors for the spread of the disease.

One question doing the rounds is where has the disease come from? Cholera has not been seen in Haiti since the 1960s. The presence of Nepalese soldiers in the United Nation’s mission to Haiti, and in the region of Haiti where the outbreak started, has been pointedly noted. Cholera is endemic in Nepal, with regular outbreaks occurring in rural regions during the wet season— and the strain in Haiti is indeed south Asian.

Even if the current outbreak does originate from the Nepalese units— which seems unlikely, as tests of the soldiers and environment around their barracks have proved negative— this detracts attention from the underlying factors which determine why it is cholera that is causing a problem in Haiti currently. These lie in the unusual pathogenic and ecological characteristics of the cholera bacterium itself, and— most importantly— the poor recovery of Haiti’s social and physical infrastructure after the January earthquake.

Vibrio cholerae is a roughly banana-shaped bacterium with a small flagellum at one pole, enabling effective propulsion through fluid. It is spread between humans by the faecal-oral route. Hence the association between outbreaks and conditions of poor sanitation (as in post-earthquake 21st century Haiti, or John Snow’s 19th century London).

Until relatively recently, it was believed that cholera was an exclusively human disease. But in the last 20-30 years there has been increasing evidence that many strains of potentially human-pathogenic vibrio are actually free-living organisms contentedly existing in a variety of aquatic environments, particularly estuaries. Copepod and algal plankton (plankton: generic term for small drifting marine organisms) can act as reservoirs for the bacteria, and cholera outbreaks have been linked to algal bloom events. In other words, cholera is actually a zoonosis, with humans only having an incidental role in the organism’s ecology.

Cholera is dangerous because of the speed and severity of the diarrhoea and (sometimes) vomiting it causes, which is induced not by the bacterium itself, but by the effects of a secreted endotoxin on the permeability of the gut wall. The WHO recommends a daily water intake of 2.2 litres for females, and 2.9 litres for males. Cholera-induced fluid loss can reach 20 litres/day in severe cases. Hence the characteristic cholera cot with its strategically-placed hole:

Treatment is simple— just make sure fluid intake matches output, until the disease has run its course. This can be an ‘oral rehydration solution’ of appropriately salty/sugary water, or intravenous fluid replacement if there is vomiting. Antibiotics can shorten the illness, but are not essential in mild cases (although in outbreak situations they will reduce the amount of infective vibrio organisms being excreted into the environment, which is a good thing).

Prevention is also simple- just ensure adequate sanitation.

In short, cholera shouldn’t be a major problem for an adequately functioning society. Unfortunately, Haiti isn’t.

If the Nepalese soldiers didn’t bring it from South Asia, it could have just as easily swum itself, by way of an algal or copepod reservoir and a passing ship’s bilge tank, or have already been there in the aquatic environment only to become pathogenic after its genome spontaneously acquired virulence factors (South Asian strains of vibrio reached the Americas some years ago, as part of the historical and ongoing seventh cholera pandemic). How and why this could happen are interesting questions. Cholera is a fascinating and incompletely understood disease, and future research may illuminate much about the processes and patterns of emerging diseases, and relationships between humans and the environment more generally.

Shipping lanes (New Scientist)

But none of this changes the fact that four hundred Haitians have already died from an easily preventable and curable disease. Proximal causes, Nepali or otherwise, do not diminish this failure of disaster response, recovery, and resilience.

Further reading:
PAHO interactive map of the Haiti cholera outbreak
Cholera in disaster situations (PAHO/WHO)
2004 Lancet article on cholera (full text top-right)

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