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Cholera

Overview

Cholera is a diarrhoeal disease caused by the Gram-negative rod bacterium Vibrio cholerae. Without treatment, symptoms can lead to severe dehydration and shock. In severe cases cholera can be fatal within a matter of hours. The majority of infected individuals remain asymptomatic but V.cholerae remains in the faeces for 7-14 days. 80-90% of reported cases are of mild to moderate severity. However, cholera does have the ability to cause endemics with pandemic potential due to the extremely short incubation period (serogroups O1 and O139). Non-O1 and non-O139 V.cholerae can cause mild diarrhoea but are unable to generate epidemics.

The World Health Organisation estimates there are 1.4-4.3 million cases per year, of which 28,000-142,000 result in fatality. Cholera is spread through contaminated water and therefore is widespread in areas with poor sanitation. Areas include sub-Saharan Africa, South and South East Asia, the Middle East, Central America and the Caribbean. There have been no originating cases of cholera in the UK for the past 100 years. However, travellers can return with the disease and England and Wales reported 6 cases during 2013-2014.

 

Signs and Symptoms

Cholera has a short incubation period ranging from less than 1 day up to 5 days. Signs and symptoms include:

  • Sudden onset of profuse watery diarrhoea

  • Vomiting

  • Fever uncommon (<5% of patients)

  • Anxiety and restlessness

  • Sunken eyes

  • Dry mucous membranes

  • Loss of skin elasticity (tenting)

  • Decreased urine and tears

  • Lethargy

  • Low blood pressure

  • Weak/absent pulse

Hypoglycaemia, seizures, coma and fever are more common in children. Hypoglycaemia in children shows a high risk of fatality.

Severe disease occurs more often in pregnancy and associated foetal loss can occur in up to 50% of cases.

 

Causes

V.cholerae is ingested through contaminated food or most commonly

water. It cannot be transmitted person-to-person as >1 million

V.cholerae (typically a glass of contaminated water) are needed to cause

illness.

Once in the small intestine, V.cholerae secretes an enterotoxin which

causes secretion of fluid and electrolytes by the small intestine. The toxin

consists of 5 B subunits which bind to the mucosal surface of the small

intestine. Activation of the A1 subunit increases cyclic AMP leading to the

blockade of sodium and chloride absorption by the microvilli. Crypt cells

then secrete chloride and enormous amounts of water through diarrhoea.

More severe forms of the disease are prevalent where gastric acidity is

low.

 

At risk groups / risk factors

Mass outbreaks of cholera typically occur in peri-urban areas with:

  • A natural disaster

  • An outbreak of war

  • Overcrowding

  • Poor living conditions

  • Disruption of water and sanitation systems

  • Lack of access to clean water

 

Diagnosis / microbiology testing

  • Dark-field microscopy shows large numbers of vibrios

  • Raised urea and creatinine levels

  • Normal or low sodium and potassium levels

  • Metabolic acidosis with high anion gap

  • Raised white cell count

 

Treatment

The main therapy goal for cholera is the rapid and safe restoration of fluid losses due to dehydration. Mild to moderate dehydration can be treated with Oral Rehydration Salts (ORS). Severe dehydration may require administration of intravenous fluids 50-100mL/kg/hour. Moderately dehydrated patients unable to tolerate oral fluids may also be given intravenous fluids.

Oral Hydration Salts (OHS) 800-1000mL/hour should be administered to patients in the maintenance phase where input is matched with output.

Antimicrobial agents may be required in severe cases to reduce the duration and volume of diarrhoea which continues during rehydration therapy. Oral antibiotics used vary on region due to antibiotic resistance and include:

1st line:

  •    Tetracycline 500mg qds for 3 days

  •    Doxycycline 300mg stat

2nd line:

  • Furazolidone 100mg qds for 3 days

  • Co-trimoxazole 960mg bd for 3 days

  • Ciprofloxacin 20mg/kg stat

  • Azithromycin 20mg/kg stat

 

Vaccines / preventative measures

There is a vaccine for cholera and it is recommended for individuals travelling to endemic areas, particularly if taking part in aid work and hence will have limited access to medical services. The vaccine is available as a drink which is taken in 2 or 3 separate doses taken 1-6 weeks apart. Effectiveness of the vaccine is estimated to be 85% in the months after infection. The level of protection will gradually reduce over time and booster doses will be required. Preventative measures should also be followed regardless of having the vaccination.

 

Preventative measures include:

  • Drinking water that has been recently boiled or that has come from a sealed bottle

  • Avoid eating ice cream or having ice in beverages

  • Avoid uncooked fruit and veg unless they have been washed in clean water (raw sewage is sometimes used as fertiliser)

  • Avoid seafood, shellfish and salads

  • Good sanitation

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