Transcript Chin_Cholera

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
•
•
•
•
•
•
•
•
•
•
•
•
•
Barua, D. & Greenough, W. B. (1992). Cholera. New York, NY: Plenum Publishing Corporation.
CDC. (2011). Cholera. Centers for Disease Control and Prevention. Retrieved on November 23, 2011 from
http://www.cdc.gov/cholera/general/.
Colwell, R. R. (2004). Infectious disease and environment: cholera as a paradigm for waterborne disease. International Microbiology. v. 7,
n. 4, p. 287-289.
Hartley, D. M., Morris, J. G., & Smith, D. L. (2006). Hyperinfectivity: a critical element in the ability of Vibrio cholerae to cause epidemics?
PLoS Medicine. v. 3, i. 2.
Hunter, P. R. (1997). Waterborne disease: Epidemiology and ecology. Chichester, West Sussex: John Wiley and Sons.
Huq, A., Small, E. B., West, P. A., Huq, M. I., Rahman, R., & Colwell, R. R. (1983). Ecological relationships between Vibrio cholerae and
planktonic crustacean copepods. Applied and Environmental Microbiology. v. 45, n. 1, p. 275-283.
Kabir, S. (2005). Cholera vaccines: the current status and problems. Reviews in Medical Microbiology. v. 16, n. 3, p. 101-116.
Kirigia, J. M., Sambo, L. G., Yokouide, A., Soumbey-Alley, E., Muthuri, L. K., & Kirigia, D. G. (2009). Economic burden of cholera in the
WHO African region. BMC International Health and Human Rights. v. 9, n. 8.
Leclerc, H., Schwartzbrod, L., & Dei-Cas, E. (2002). Microbial agents associated with waterborne diseases. Critical Reviews in
Microbiology. v. 28, n. 4, p. 371-409.
Magny, G. C., Murtugudde, R., Sapiano, M. R. P., Nizam, A., Brown, C. W., Busalacchi, A. J., Yunus, M., Nair, G. B., Gil, A. I., Lanata, C.
F., Calkins, J., Manna, B., Rajendran, K., Bhattacharya, M. K., Huq, A., Sack, R. B., & Colwell, R. R. (2008). Environmental
signatures associated with cholera epidemics. Proceedings of the National Academy of Sciences of the United States of
America. v. 105, n. 46.
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.
Reidl, J. & Klose, K. E. (2002). Vibrio cholerae and cholera: out of the water and into the host. FEMS Microbiology Reviews. v. 26, p. 125139.
WHO. (2011). Global epidemics and impact of cholera. World Health Organization. Retrieved on November 23, 2011 from
http://www.who.int/topics/cholera/impact/en/index.html.