cholera

Last edited 02/2020

Cholera is an acute infectious disease endemic and epidemic in Asia.

It is caused by Vibrio cholerae, a gram-negative rod found in coastal waters and estuaries (1).

• more than 200 serogroups have been identified based on the O antigen of the lipopolysaccharide
• only O1 and O139 serogroups are responsible for epidemic cholera
• O1 is responsible for majority of outbreaks while O139 (first identified in Bangladesh in 1992) is confined to South East Asia (2)
• O1 is further divided in two biotypes
• classic
• El Tor - is able to survive longer in nature, can cause subclinical cases, has a longer faecal excretion of the organism, and can be transmitted from case to case or via food and water
• it is further divided into subtypes  - Ogawa or Inaba
• worldwide, V. choleraeEl Tor is currently the predominant biotype and Ogawa the predominant subtype.
• non-O1 and non-O139 V. cholerae can cause mild diarrhoea but do not cause epidemics(2) 

The incubation period ranges between 12 h and 5 days (1).

Most people infected with V. cholerae tend to have mild-to-moderate diarrhoea - however, if left untreated, cholera can be one of the most rapidly fatal infectious illnesses known (1,2)

Cholera is a notifiable disease in the UK (3).

Summary:

Cause:

• Toxigenic Vibrio cholerae serogroups O1 (biotypes ‘classical’ and ‘El Tor’) and O139
• Non-O1 and non-O139 may cause milder gastroenteritis but not cholera

Reservoir:

• Humans and the environment

Transmission:

• Transmission is via the faecal-oral route primarily via drinking water contaminated by faeces
• Consumption of contaminated food, especially shellfish, is also a route of transmission
• A large infectious dose is required so secondary transmission is not likely in countries with good sanitation systems (e.g. UK).

Incubation period:

• Usually 24-72 hours (range 2 hours - 5 days) but is dependent on the dose ingested

Infectivity:

• Cases are considered infectious whilst diarrhoea is present and up to 7 days after. Since secondary transmission is unlikely in the UK due to good sanitation, exclusion for 48 hours after first normal stool is usually applied. Occasionally, some cases might become ‘carriers’ for a few months

Notes:

• Large epidemics are common following the breakdown of public health measures such as areas experiencing war, famine and natural disasters
• A vaccination against cholera is available but is not considered to be highly effective and is therefore not generally recommended (4)

Reference:

• (1) Harris JB et al. Cholera. Lancet. 2012;379(9835):2466-76
• (2) World Health Organization. Cholera. Fact Sheet 107. July 2012
• (3) Immunisation Against Infectious Disease - "The Green Book".Chapter 14 Cholera (January 2020)
• (4)PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections