|Guidelines for Cholera Control (WHO - OMS, 1993, 68 p.)|
Most cholera infections are mild; patients may have no symptoms or only mild diarrhoea. In a minority of cases, however, there is rapid onset of severe watery diarrhoea and vomiting, resulting in the loss of large amounts of fluid and salts from the body. Patients become thirsty, stop urinating, and quickly become weak and dehydrated. Patients with severe cholera often complain of cramps in the stomach, arms, or legs.
All cases of cholera should be treated immediately. If treatment is delayed or inadequate, death from dehydration and circulatory collapse may follow very shortly.
There are more than 60 serogroups of Vibrio cholerae, but only serogroup O1 causes cholera. Vibrio cholerae O1 occurs as two biotypes - classical and El Tor. Each biotype also occurs as two serotypes - Ogawa and Inaba. The El Tor biotype has caused almost all of the recent cholera outbreaks, although cases caused by the classical biotype still occur on the Indian subcontinent. The El Tor biotype also causes a higher proportion of asymptomatic infections than the classical biotype and survives longer in the environment. It can live in association with certain aquatic plants and animals, making water an important reservoir for infection.
Cholera is acquired by the ingestion of an infectious dose of cholera vibrios. Faecally contaminated water is usually the vehicle for transmission of infection, either directly or through the contamination of food. Food may also be contaminated by the soiled hands of infected persons.
The dose of Vibrio cholerae O1 required to produce illness depends on the susceptibility of the individual. It can be affected by the level of acidity in the stomach (the vibrio is destroyed at pH 4.5 or lower), and by immunity produced by prior infection with Vibrio cholerae O1. In endemic areas, breast-feeding protects infants and young children.
Box 1. Common sources of infection
that has been contaminated at its source (e.g. by faecally contaminated surface water entering an incompletely sealed well) or during storage (e.g. by contact with hands soiled by faeces), and ice made from contaminated water.
· Food contaminated during or after preparation
e.g. milk, cooked rice, lentils, potatoes, beans, eggs, and chicken.
particularly shellfish, taken from contaminated water and eaten raw or insufficiently cooked.
· Fruit and vegetables
grown at or near ground level and fertilized with night-soil, irrigated with water containing human waste, or "freshened" with contaminated water, and then eaten raw.