Cholera
Tim Chin
Limnology
December 8, 2011
Waterborne Diseases
• Illnesses transmitted through the consumption of contaminated
water
• Water acts as a passive host for waterborne pathogens
• Caused by a bacterial, viral, or protozoal agent
Cholera
• The first waterborne disease to be associated with water as its
source
• Characterized by profuse watery diarrhea, sometimes along with leg
cramps and vomiting
• Only 5% of infected individuals display severe symptoms
• Can cause death in untreated cases within a matter of hours from
dehydration and shock
• Caused by the bacteria Vibrio cholerae
Vibrio cholerae
• A member of the Vibrionaceae
family
• A short curved bacilli
• Gram-negative
• Motile
Life Cycle and Ecology
• Was once believed to be a obligate pathogen, unable to survive
outside of the human intestine
• Has been found to be a facultative pathogen
• Has both human and environmental stages in its life cycle
• An indigenous member of oceanic and aquatic ecosystems
• Thrives best in brackish environments
Life Cycle and Ecology
• Organisms which are
significantly similar to Vibrio
cholerae have been found
around deep ocean
hydrothermal vents
• Ancestral home has been
speculated to be the deep
ocean due to its affinity for salt
and the samples found near
oceanic hydrothermal vents
Life Cycle and Ecology
• Can exist as both a free-living
organism and a resilient biofilm
aggregate
• Possesses the ability to
secrete chitinase, allowing it to
colonize chitinous surfaces
• Is often found as a biofilm on
copepods, specifically on the
oral and egg sac regions
Life Cycle and Ecology
• The human stage of its life cycle begins once enough Vibrio
cholerae are ingested by a human host
• 10^6 - 10^11 colony-forming organisms is the infectious dose
• Only 10^3 organisms need to be consumed if the stomach’s acidity
is neutralized beforehand
• Colonizes the small intestine where it induces a diarrheal discharge
Life Cycle and Ecology
• Hyperinfective Vibrio cholerae leaves the human host alongside
fecal matter and collects on temporary reservoirs
• Hyperinfective state lasts for several hours, allowing for a rapid
localized spread
• Repeats the cycle as more humans are infected
Life Cycle and Ecology
Vibrio cholerae Classification
• Categorized into serogroups based on variations in somatic O
antigens
• About 200 serogroups of Vibrio cholerae are known to exist
• Only serogroups O1 and O139 are associated with cholera
epidemics and pandemics
• Members of the O1 and O139 serogroups possess genes which
enhance their virulence
• Virulence genes code for the production of cholera-toxin and toxin
co-regulated pilus colonizing factor
Disease Mechanism
• Secreted cholera-toxin binds to receptors on epithelial cells of the
intestines and enters the cells through endocytosis
• Causes a cascade of biochemical reactions, including a high
production of cyclic AMP, an inhibition of sodium uptake, and the
secretion of chloride ions
• Biochemical processes cause an alkaline and electrolyte-rich fluid to
build up in the intestinal lumen
• Fluid buildup provokes a diarrheal discharge
Historical Cholera Outbreaks
• Records of cholera outbreaks go back as far as 2,500 years
• Modern history of cholera starts in 1817, where an epidemic in India
spread across the continent to southeast Asia, becoming the first
cholera pandemic
• 5 additional pandemics have occurred in the 19th century which
mostly affected the continents in the southern hemisphere and later
extended to Europe and North America
• The seventh and most recent pandemic which lasted from 1961 to
1994 spread to Africa and South America
Historical Cholera Outbreaks
Cholera Incidence and Spread
• Outbreaks are common around September when zooplankton
populations increase due to phytoplankton blooms
• Tends to arise in impoverished areas where sanitary procedures are
lacking
• Affected by temperature, salinity, and pH
• Global weather patterns also play a role
– Positive link between the number of cholera cases and the occurrence
of El Niño
Effects on Health and Economy
• 3-5 million cases of cholera every year
• Causes around 100,000 deaths each year
• Costs associated with a cholera outbreak include the costs of
healthcare, medicine, and testing
• Other economical burdens are a loss of productive time and
decreases in both trade and tourism
• For example, a 1991 cholera outbreak in Peru cost the country over
$770,000,000
Present Concerns
• Cholera poses a threat to
developing countries, where
people lack access to clean
water
• Not a concern in the United
States or other developed
countries
Cholera Treatment
• Cholera is easily treatable,
reducing fatalities to far below
1%
• Treated with rehydration
therapy
– Through fluid intake
– Rehydration salts
• Antibiotics are administered in
severe cases
Cholera Prevention
• Securing a source of clean
water
• Construction of water
treatment plants
• Adopting better sanitation
practices
• Education
Image Sources
•
http://images.wellcome.ac.uk/indexplus/result.html?_IXMAXHITS_=1&_IXACTION_=query&_IXFIRST_=1&_IXem
ailreal=true&_IXbox=259048&_IXSPFX_=templates%2Ft&_IXFPFX_=templates%2Ft
•
http://www.grida.no/graphic.aspx?f=series/vg-water2/0291-choleraspread-EN.jpg
•
http://earthobservatory.nasa.gov/Features/OceanCarbon/
•
http://www.chinookmed.com/cgi-bin/category.cgi?item=18120
•
http://jhyoung.myweb.uga.edu/Waterborne.html
•
http://www.noc.soton.ac.uk/chess/education/edu_htv.php
•
http://www.waterencyclopedia.com/Tw-Z/Wastewater-Treatment-and-Management.html
•
http://neerfoundation.org/water-borne-diseases.html
•
Nelson, E. J., Harris, J. B., Morris, J. G., Calderwood, S. B., & Camilli, A. (2009). Cholera transmission: the host,
pathogen, and bacteriophage dynamic. Nature Reviews | Microbiology. v. 7, p. 693-702.
References
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