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 Something in the Water: Tracing the Cholera Outbreak in Haiti April 13, 2012

Posted by srstone in Biology, Environment/Conservation, Evolution, Genetics, Health, Medicine, Policy, Science & Culture.
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 Something in the Water

Cholera Under the Microscope

When we go to the sink to get a glass of water from the sink, we trust that what the water is comprised of is safe for us to drink.  Most of us don’t give a thought as to what could be in it.  This is one of the luxuries of living in a first world country.  However, those in third world countries, such as Haiti, are not so fortunate.  Shortly after the earthquake in Haiti in 2010, a cholera outbreak occurred.  When an outbreak like this occurs, the goal is to not only check the spread of the disease among Haitians, but to prevent the bacteria from swapping DNA with other cholera strains in the country to form a more dangerous bug much harder to treat.

Antibiotic-resistant Cholera: Mechanisms explored

Bacteria reproduce asexually by a process called binary fission.  Binary fission causes two genetically identical bacterial cells to be produced.  If this was the only method bacteria had to procreate, treating a disease with antibiotics would be simple.  Antibiotics aim to either kill bacteria directly or hamper their ability to grow and reproduce.  This can be done by crippling the production of the bacterial cell wall and inhibiting protein, DNA, or RNA synthesis. 

However, when we put our bodies on the attack with the use of antibiotics, bacteria respond by playing their side with different defensive mechanisms.  Some of these mechanisms include changing the permeability of their membranes.  For example, bacteria can decrease the number of channels available for the antibiotics to enter the cell.  Another mechanism works by changing the actual physical structure of the antibiotic once it enters the cell so that the drugs can’t bind the way they were designed to in order to have an effect.  Although both of these mechanisms prevent antibiotics from carrying out their job, bacterial recombination is the most common form of developing antibacterial resistance.  When this happens, bacteria gain genetic variation by swapping DNA with other bacteria.  This allows the bacteria to acquire resistance to the drug.  A plasmid, which is a circular piece of DNA, can encode resistance to multiple antibiotics. Thus if one bacterial cell in the environment has evolved resistance to an antibiotic, it can easily share that information with other surrounding bacteria leading to an epidemic of widespread antibacterial resistance.   A transposon, known as a “jumping gene”, can jump ship from DNA to DNA molecule.  The transposon then becomes part of the plasmid.

Where did it come from?

Cholera, which had never been seen before in Haiti prior to the earthquake, had the advantage.  Nations offering their help focused on the earthquake recovery while cholera entered Haiti under the radar.  Reducing the fatality rate from cholera has been a success; however the response was slow to fully develop.  The most likely story is that cholera spawned from a Nepalese volunteer at the Minustah base.  Understandably, no one wanted to take responsibility for bringing an epidemic to a country that already needed all the help they can get. 

To resolve the “blame-game”, Danish and American scientists collaborated to determine where the cholera came from.  Haiti’s cholera strain and Nepal’s cholera strain of the bacteria were examined using the most comprehensive type of analysis: whole-genome sequence typing.  Virtually identical, the Nepalese were forced to accept blame.  Another method, pulse-field gel electrophoresis was also used as evidence.  Scientists found that cholera erupted in Nepal in July 2010, but was under control the following month in August.  Unfortunately, this was the same month that Nepalese soldiers left for a recovery mission in Haiti.        

Resolutions?

Through the application of genetics, the cholera strain has been identified.  Unfortunately, this doesn’t solve Haiti’s problems.  Only 12% of the population has access to piped, treated water.  The rest find their water in rivers and wells.  These are the same rivers that contain feces and that Haitians wash their clothes in.  Vaccinations and supportive care will aid in the conquering of cholera, but until safe water is more readily accessible, the country needs to be prepared for round two.

A Typical Haitian Laundry Room

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