Cholera Tim Chin Limnology December 8, 2011. Waterborne Diseases Illnesses transmitted through the consumption of contaminated water Water acts as a passive.

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&_IXemailreal=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

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