one health lecture 7- cholera Flashcards
what is cholera?
Infection of the intestine by Vibrio cholerae.
Usually, an acute diarrhoeal infection in healthy individuals, however it can become severe.
what are the symptoms of cholera?
-Profuse, watery diarrhoea – ‘rice water stools’ up to 1 litre/hour
-Leg cramps
-Vomiting
-Poor skin elasticity
-Severe dehydration leads to >100,000 deaths annually
what is the cholera toxin?
-AB toxin, similar to labile toxin found in E. coli
-Complex is made up of 6 protein subunits
1 x A subunit (enzymatic)
5 x B subunits (binding)
how does cholera invade the body?
1- Ingestion of contaminated food/water, normally in areas with poor sanitation.
Symptoms can present from 3 h - death within hours.
2- V. cholerae rapidly increases in the intestine, releasing a toxin – CHOLERA TOXIN (CT).
3- CT prevents intestine from absorbing water from food, resulting in diarrhoea and severe dehydration.
how do the levels of cAMP inside the host cell increase?
1- CT binds to host cells via B subunit and forms a toxin-containing vacuole.
2- On route to the ER, A subunit is cleaved and A1 relocates to the cytoplasm.
3- CT binds to G protein, constant stimulation of adenylate cyclase
- cAMP produced.
4- High cAMP activates ion channels (CFTR) produced.
Escaping water enters the intestinal lumen, resulting in diarrhoea.
what is vibrio cholerae?
Gram-negative, comma shaped bacterium
Facultative anaerobe
Has a pilus and flagellum
Pathogenesis due to toxin and pilus
Toxin Co-regulated Pili (TCP)
-Formation of microcolonies
-Colonisation of intestine
-Receptor to CTXφ
what is the CTX bacteriophage?
-Cholera toxin filamentous phage (CTXφ) can infect non-pathogenic Vibrio species with virulence genes, encoding cholera toxin.
-Horizontal transfer of genes can confer pathogenicity
what is the case study in London with cholera?
-During the 3rd pandemic (1849), a series of cholera outbreaks lead to >10,000 deaths in London
-Suspected water, unwashed hands and shared food was the source of infection
-Mapped the location of those infected and found they all used a water pump on Broad Street
-Removal of the handle resulted in a decline of infections
-Contaminated water was identified as the source of cholera outbreak
what is the incidence of cholera?
-This does not fully represent the true incidence.
~80% cases are not reported.
-Estimated to be 1.3 – 4.0 million cases of cholera every year, with up to 143,000 deaths annually.
Many countries reporting cholera are endemic for the disease – repeated occurrence.
Epidemics can also occur – sudden unexpected outbreak affecting many people.
58 countries reporting outbreaks - Haiti, Dominican Republic
what is the treatment for cholera?
-Severe cases need to be treated with oral rehydration, therefore delivery clean water and sanitation is essential for controlling cholera
-844 million people still lack even a basic drinking water service
what is the role of cholera to the environment?
-V. cholerae is a natural inhabitant of the aquatic environment, making cholera one of the most prevalent water-related infections.
-Vast majority of cholera outbreaks originate from coastal locations, linking the environment to disease.
what is the Bay of Bengal?
-The Bay of Bengal has been described as the ‘native homeland of cholera’.
-Sequencing of strains from the 7th pandemic revealed they all arose from a single source in the Bay of Bengal.
-V. cholerae is not just a human pathogen spread by oral-faecal route, it can survive in coastal waters for extended periods of time.
how is copepod essential to the survival of v cholerae
V. cholerae has a complex life cycle where it can exist in various states and associate with other organisms
Important role in the transmission and survival ofV. cholerae.
what is the copepod relationship?
-V. cholerae colonises the gut and egg masses of copepods, establishing a commensal association and utilising chitin as a carbon source.
-Copepods feed on algae and therefore the population of these zooplankton is strongly associated with algae blooms.
V. cholerae forms biofilms within copepods
Protective environment from external stresses
Copepod exoskeleton is made up of chitin (insoluble), bacteria break this down to provide useful carbon source in seawater
This association with copepods is crucial for the epidemiology of cholera
what is satellite based remote sensing?
Satellite sensing can allow the detection of microbes by the use of space-based sensors, providing a new view of our oceans.
DIRECT - microbes can be seen by sensors, identified on optical properties (bioluminescence from blooms).
INDIRECT – identification and quantification by physical or physiological properties (chlorophyll in cyanobacteria).
-V. cholerae can be estimated based on sea temperature and phytoplankton abundance.
